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NCERT Solutions for Class 10 Science Chapter 8 How do Organisms Reproduce ?

NCERT Solutions for Class 10 Science Chapter 8 How do Organisms Reproduce?

NCERT Solutions for Class 10 Science Chapter 8 How do Organisms Reproduce?  includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

 

Page No: 128

1. What is the importance of DNA copying in reproduction?

Answer

DNA is the genetic material present in the cells of all organisms. The genetic information from generation to generation is carried by DNA. It is therefore possible for the organism to produce organism of its own type due to DNA copying only. For the inheritance of traits of the parent, DNA copying is a must. DNA copying also brings about variation ,which forms the basis for the origin of new species.

2. Why is variation beneficial to the species but not necessarily for the individual?

Answer

Variations are beneficial to the species than individual because sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult. For example, if the temperature of water increases suddenly, then most of the bacteria living in that water would die. Only few variants that are resistant to heat would be able to survive. However, if these variants were not there, then the entire species of bacteria would have been destroyed. Thus, these variants help in the survival of the species. However, all variations are not necessarily beneficial for the individual organisms.

Page No: 133

1. How does binary fission differ from multiple fission?

Answer

In binary fission a single cell divides into two equal halves.Amoeba and Bacteria divide by binary fission.
In multiple fission, a single cell divides into many daughter cells simultaneously. Plasmodium divide by multiple fission.



2. How will an organism be benefited if it reproduces through spores?

Answer

 

Advantages of spore formation:
→ Large numbers of spores are produced in one sporangium.
→ Spores are distributed easily by air to far-off places to avoid competition at one place.

→ Spores are covered by thick walls to prevent dehydration under unfavourable conditions.


3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?

Answer

Higher complex organisms cannot give rise to new individuals through regeneration because complex organisms have organ-system level of organization. All the organ systems of their body work together as an interconnected unit. They can regenerate their lost body parts such as skin, muscles, blood, etc. However, they cannot give rise to new individuals through regeneration.

4. Why is vegetative propagation practised for growing some types of plants?

Answer

Vegetative propagation is practiced for growing some types of plants because of following advantages:

→ It is used to grow a plant in which viable seeds are not formed or very few seeds are produced such as Orange, Banana, Pineapple.

→ It helps to introduce plants in new areas where the seed germination fails to produce mature plant due to change in environmental factors and the soil.→ It is more rapid, easier and cheaper method.
→ By this method a good quality of a race or variety can be preserved.

 

5. Why is DNA copying an essential part of the process of reproduction?

Answer

DNA copying is an essential part of reproduction as it passes genetic information from parents to offspring. It determines the body design of an individual. The reproducing cells produce a copy of their DNA through some chemical reactions and result in two copies of DNA. The copying of DNA always takes place along with the creation of additional cellular structure. This process is then followed by division of a cell to form two cells.

Page No: 140

1. How is the process of pollination different from fertilization?

Answer

Pollination is the process of transfer of pollens from anther to stigma. It occurs with the help of certain pollinators such as air, water, birds, or some insects.
Fertilization, is the fusion of the male and female gametes. It occurs inside the ovule and leads to the formation of zygote.



2. What is the role of the seminal vesicles and the prostate gland?

Answer

The secretions from seminal vesicles and prostate glands lubricate the sperms and provide a fluid medium for easy transport of sperms. Their secretion also provides nutrient in the form of fructose, calcium, and some enzymes.

3. What are the changes seen in girls at the time of puberty?

Answer

The changes seen in girls at the time of puberty are:
→ Increase in breast size and darkening of skin of the nipples present at the tips of the breasts.
→ Appearance of hair in the genital area.
→ Appearance of hair in other areas of skin like underarms, face, hands, and legs.
→ Increase in the size of uterus and ovary.
→ Beginning of menstrual cycle.
→ More secretion of oil from the skin, which results in the appearance of pimples.

4. How does the embryo get nourishment inside the mother’s body?

Answer

After fertilization the lining of uterus thickens and is richly supplied with blood to nourish the growing embryo. The embryo gets nutrition from the mother’s blood with he help of a special tissue called placenta. It is embedded in the uterine wall. Placenta contains Villi on the embryo’s side of the tissue and blood spaces on mother’s side surrounding the villi. This provides a large surface from mother to the embryo and waste products from embryo to mother.

5. If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?

Answer

No, because copper-T will not prevent contact body fluids. Thus it will not protect her from sexually transmitted diseases.

Exercise

1. Asexual reproduction takes place through budding in
(a) amoeba.
(b) yeast.
(c) plasmodium.
(d) leishmania.
► (b) yeast.

2. Which of the following is not a part of the female reproductive system in human beings?
(a) Ovary
(b) Uterus
(c) Vas deferens
(d) Fallopian tube
► (c) Vas deferens

3. The anther contains
(a) sepals.
(b) ovules.
(c) carpel.
(d) pollen grains.
► (d) pollen grains.

4. What are the advantages of sexual reproduction over asexual reproduction?

Answer

Advantages of sexual reproduction:
→ In sexual reproduction, more variations are produced. Thus, it ensures survival of species in a population.
→ The new formed individual has characteristics of both the parents.

→ Variations are more viable in sexual mode than in asexual one. This is because in asexual reproduction, DNA has to function inside the inherited cellular apparatus.

5. What are the functions performed by the testis in human beings?

Answer

Functions of testes:
→ Produce sperms, which contain haploid set of chromosomes of father.
→ Produce a hormone called testosterone, which brings about secondary sexual characters in boys.

6. Why does menstruation occur?

Answer
 
Menstruation is a process in which blood and mucous flows out every month through the vagina. This process occurs every month because one egg is released from the ovary every month and at the same time, the uterus (womb) prepares itself to receive the fertilized egg. Thus, the inner lining of the uterus gets thickened and is supplied with blood to nourish the embryo. If the egg does not get fertilised, then the lining of the uterus breaks down slowly and gets released in the form of blood and mucous from the vagina.

7. Draw a labelled diagram of the longitudinal section of a flower.

Answer
 
8. What are the different methods of contraception?

Answer
 
The contraceptive methods can be broadly divided into the following types:
→ Natural method: It involves avoiding the chances of meeting of sperms and ovum. In this method, the sexual act is avoided from day 10th to 17th of the menstrual cycle because during this period, ovulation is expected and therefore, the chances of fertilization are very high.
→ Barrier method: In this method, the fertilization of ovum and sperm is prevented with the help of barriers. Barriers are available for both males and females. Condoms are barriers made of thin rubber that are used to cover penis in males and vagina in females.
→ Oral contraceptives: In this method, tablets or drugs are taken orally. These contain small doses of hormones that prevent the release of eggs and thus fertilization cannot occur.
→ Implants and surgical methods: Contraceptive devices such as the loop or Copper-T are placed in uterus to prevent pregnancy. Some surgical methods can also be used to block the gamete transfer. It includes the blocking of vas deferens to prevent the transfer of sperms known as vasectomy. Similarly, fallopian tubes of the female can be blocked so that the egg will not reach the uterus known as tubectomy.

9. How are the modes for reproduction different in unicellular and multicellular organisms?

Answer

In unicellular organisms, reproduction occurs by the division of the entire cell. The modes of reproduction in unicellular organisms can be fission, budding, etc. whereas in multicellular organisms, specialised reproductive organs are present. Therefore, they can reproduce by complex reproductive methods such as vegetative propagation, spore formation, etc. In more complex multicellular organisms such as human beings and plants, the mode of reproduction is sexual reproduction.

10. How does reproduction help in providing stability to populations of species?

Answer

Reproduction is the process of producing new individuals of the same species by existing organisms of a species, so, it helps in providing stability to population of species by giving birth to new individuals as the rate of birth must be at par with the rate of death to provide stability to population of a species.

11. What could be the reasons for adopting contraceptive methods?

Answer

Contraceptive methods are mainly adopted because of the following reasons:
→ To prevent unwanted pregnancies.
→ To control population rise or birth rate.
→ To prevent the transfer of sexually transmitted diseases.

Important Links

Quick Revision Notes –Chapter 8 How do Organisms Reproduce?  

Most Important Questions- Chapter 8 How do Organisms Reproduce? 

Important MCQs- Chapter 8 How do Organisms Reproduce?

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NCERT Solutions for Class 10 Science Chapter 7 Control and Coordination

NCERT Solutions for Class 10 Science Chapter 7 Control and Coordination

NCERT Solutions for Class 10 Science Chapter 7 Control and Coordination  includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

 

Page No: 119

1. What is the difference between reflex action and walking?

Answer

Reflex action is involuntary action which means it is not under control of brain only involves spinal cord, it is rapid, thus gives instant response to the stimulus and not affected by our thinking.
But walking is a voluntary action controlled by brain involves central nervous system and spinal cord both and affected by our thinking.

2. What happens at the synapse between two neurons?

Answer

The synapse is the tiny gap (not seen by naked eyes) between two adjacent neurons. This information, acquired at the end of the dendritic tip of a nerve cell sets off a chemical reaction that creates an electrical impulse. This impulse travels from the dendrite to the cell body, and then along the axon to its end. At the end of the axon, the electrical impulse sets off the release of some chemicals. These chemicals cross the gap, or synapse, and start a similar electrical impulse in a dendrite of the next neuron. This is the process how nervous impulses travel in the body. Similar synapse finally allows delivery of such impulses from neurons to other cells, such as muscles cells or gland.

3. Which part of the brain maintains posture and equilibrium of the body?

Answer

Cerebellum

4. How do we detect the smell of an agarbatti (incense stick)?

Answer

When agarbatti burns, it produces pleasant smell, which is detected by the olfactory receptor present inside the nose. The action of smell generates the electrical impulse. These impulses are carried to the sensory area of brain(forebrain-cerebrum). Thus we detect the smell of agarbatti.
All information from our environment is detected by the specialised tips of some nerve cells. These receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue, and so on. So gustatory receptors will detect taste while olfactory receptors will detect smell.

5. What is the role of the brain in reflex action?

Answer

Reflex action occurs in spinal cord. The brain and spinal cord constitute the central nervous system. They receive information from all parts of the body and integrate it.
 
Page No. 122

1. What are plant hormones?

Answer

The chemical substances produced in plants which control growth, development and responses in plants, are called plants plant hormones.
For example: Auxins, Gibberellins, Cytokinins and Abscisic acid.

2. How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?

Answer

The main differences between the movement of the leaves of a sensitive plant and the movement of a shoot towards light are as follows:

Movements of leaves of sensitive plants Movement of a shoot towards light
1. It is not a growth movement. 1. It is a growth movement.
2. It is a nastic movement which does not depend on the direction of stimulus. 2. It is a tropic movement which depends on the direction of stimulus.

3. Give an example of a plant hormone that promotes growth.

Answer

Auxin

4. How do auxins promote the growth of a tendril around a support?

Answer

Auxin is a plant growth hormone. When the tip of the tendril touches a support, then the auxins present on its tip moves to the side of tip which is away from the support, so, due to more auxins in its tendrils away from the support grows faster.
 
5. Design an experiment to demonstrate hydrotropism.
 
Answer
 
Hydro’ means water.  Hydrotropism means growth towards water.

Materials Required: Seed, A big container, Porous water pot, water and Sand.

Procedure:
• The tray should be big enough to accommodate the porous pot.
• Fill the tray with sand and insert some seeds in it.
• Make a pit in the sand and insert the porous pot in it.
• Fill the porous pot with water. • Leave the set up for about a week.

Observation:
After a week when seeds are taken out, it is observed that roots grow in the direction of the porous pot. This shows hydrotropic movement in roots.
 
Page No. 125
 
1. How does chemical coordination take place in animals?
 
Answer
 
The chemical coordination in animals takes place by the action of chemical called hormones. They are produced in certain glands in body in very small amount and poured directly in the blood. They are target based means works on particular organs and these organs are called target organs. The hormones control and coordinate various functions of the body such as development, growth, sexual changes etc.
 
2. Why is the use of iodised salt advisable?
 
Answer
 
Iodine is necessary for the thyroid gland to make thyroxin hormone. Thyroxin regulates carbohydrate, protein and fat, metabolism in the body so as to provide the best balance for growth. Iodine is essential for the synthesis of thyroxin. In case iodine is deficient in our diet, there is a possibility that we might suffer from goitre. One of the symptoms in this disease is a swollen neck.
 
3. How does our body respond when adrenaline is secreted into the blood?
 
Answer
 
Adrenaline is secreted directly into the blood and carried to different parts of the body. The target organs or the specific tissues on which it acts include the heart. As a result, the heart beats faster, resulting in supply of more oxygen to our muscles. The blood to the digestive system and skin is reduced due to contraction of muscles around small arteries in these organs. This diverts the blood to our skeletal muscles. The breathing rate also increases because of the contractions of the diaphragm and the rib muscles. All these responses together enable the animal body to be ready to deal with the situation. Such animal hormones are part of the endocrine system which constitutes a second way of control and coordination in our body.
 
4. Why are some patients of diabetes treated by giving injections of insulin?
 
Answer
 
 
Diabetes patients as a treatment, they might be taking injections of insulin. This is a hormone which is produced by the pancreas and helps in regulating blood sugar levels. If it is not secreted in proper amounts, the sugar level in the blood rises causing many harmful effects.
Exercises
 
1. Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin
 
Answer
 
(d) Cytokinin
 
2. The gap between two neurons is called a
(a) dendrite.
(b) synapse.
(c) axon.
(d) impulse.
 
Answer
 
(b) synapse.
 
Page No. 126
 
3. The brain is responsible for
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
 
Answer
 
(d) all of the above.
 
4. What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
 
Answer
 
All information from our environment is detected by the specialised tips of some nerve cells. These receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue, and so on. So gustatory receptors will detect taste while olfactory receptors will detect smell. We detect that we are touching a hot object by the action of receptors present on various organs or tissues.
If olfactory receptor not works properly then we are not able to smell things like aggarbatti, perfumes, flavour of food.
 
5. Draw the structure of a neuron and explain its function.
 
Answer
 
A neurons consists of three parts;
(i) Cell body: It is a typical animal cell which contains cytoplasm and a nucleus.
 
(ii) Dendrites: A number of long and thin fibres comes out from the cell body of the neurons, they are nerve fibre. The shorter fibres on the cell body of neurons are called dendrites.
 
(iii) Axon: The longest fibre on the cell body of neurons is called axon. It has an insulating and protective sheath (or cover)of myelin around it.
 
 
Function:
The information, acquired at the end of the dendritic tip of a nerve cell, sets off a chemical reaction that creates an electrical impulse. 
This impulse travels from the dendrite to the cell body, and then along the axon to its end. At the end of the axon, the electrical impulse sets off the release of some chemicals. 
These chemicals cross the gap, or synapse, and start a similar electrical impulse in a dendrite of the next neuron. This is a general scheme of how nervous impulses travel in the body. 
A similar synapse finally allows delivery of such impulses from neurons to other cells, such as muscles cells or gland. 
It is thus no surprise that nervous tissue is made up of an organised network of nerve cells or neurons, and is specialised for conducting information via electrical impulses from one part of the body to another.
 
6. How does phototropism occur in plants?
 
Answer

Photo means light. The response of plant towards the environmental triggers, light which change the directions that plant parts grow in is called phototropism.
The directional, or tropic, movements can be either towards the light, or away from it. So, in two different kinds of phototropic movement, shoots respond by bending towards light while roots respond by bending away from it.

For example: Sunlight bends towards the sun from where the light is coming. This is the response of sunflower towards the plants.
 
7. Which signals will get disrupted in case of a spinal cord injury?
 
Answer
 
Reflex actions are involuntary actions and controlled by the spinal cord thus, gets disrupted in case of spinal cord injury.
 
8. How does chemical coordination occur in plants?
 
Answer

Plants do not have nervous system but still sense the things because of stimulus such as gravity, light, chemicals(hormones), water, touch (touch -me -not plant).Hormones are responsible for the chemical coordination of plants by integrating their behaviour by affecting growth of a plant resulting in movement of that plant part in response to a stimulus. When sunlight falls on the shoot from one side, the auxins hormone causes the shady side of the shoot to grow faster, making the shoot bend towards sunlight.
 
9. What is the need for a system of control and coordination in an organism?

Answer

Controlled movement must be connected to the recognition of various events in the environment, followed by only the correct movement in response. In other words, living organisms must use systems providing control and coordination. In keeping with the general principles of body organisation in Multicellular organisms, specialised tissues are used to provide these control and coordination activities.

(i) Coordination is needed for all human activities like, thinking and behaviour. Our breathing process, hearts beats, we dance, read, write by the action of our nervous system. Our nervous system gets information from surroundings and processes it and then respond according to it. The endocrine system (hormonal system) helps in integrating various metabolic activities like reproduction, development, all reflex actions (cope up with various give up situations).

(ii)The hormonal system in plants helps in process of photosynthesis; they need carbon dioxide, water and sunlight. The stomatal opening in leaves opens up to allow in carbon dioxide gas, the roots bend towards water and the stem grows towards sunlight, the tendrils in climbing pants are supported by the hormonal system of the plant body.

Thus, we have need of control and coordination system in an organisms.
10. How are involuntary actions and reflex actions different from each other?

Answer

Involuntary actions are not controlled by us they are independent process means there is no stimulus involved in these actions but reflex action is also involuntary in nature but they involves stimulus means functions or respond according to it.
For example; 
Involuntary actions: heart beat, breathing process; etc.
Reflex actions: stepping out in bright light, changes in size of pupil of eyes.
11. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.

Answer

Difference between nervous and hormonal mechanism:

Nervous system Hormonal system
1. Made up of neurons (nerve cell). 1. Made of secretory cells (glands).
2. Messages transmitted in the form of electrical impulses. 2. Messages transmitted in the form of chemicals called hormones.
3. Messages transmitted along nerve fibre. 3. Messages transmitted along blood stream.
4. Effect of message usually lasts for a very short while. 4. Effect of message usually lasts longer.
5. Messages travel very quickly. 5. Messages travel more slowly.

12. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
 
Answer

The movement of sensitive plants leaves takes place due to the sudden loss of water in the pad-like swelling (called pulvini) at the base of all the leaves. Pulvini limp gets drooped and folded due to the loss of water. On the other hand, the movement of our legs take place due to pull in the muscles of legs on the leg bones.

Important Links

Quick Revision Notes –Chapter 7 Control and Coordination  

Most Important Questions- Chapter 7 Control and Coordination 

Important MCQs- Chapter 7 Control and Coordination

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NCERT Solutions for Class 10 Science Chapter 6 Life Processes

NCERT Solutions for Class 10 Science Chapter 6 Life Processes 

NCERT Solutions for Class 10 Science Chapter 6 Life Processes  includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

 

Page No: 95

1. Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?

Answer

Unlike the unicellular organisms, the multi-cellular organisms have complex body structures with specialized cells and tissues to perform various necessary functions of the body. Since these cells are not in direct contact with surrounding environment so, simple diffusion cannot meet the oxygen requirement of all these cells.

2. What criteria do we use to decide whether something is alive?

Answer

Any visible movement such as walking, breathing, or growing is generally used to decide whether something is alive or not. However, a living organism can also have movements, which are not visible to the naked eye. Therefore, the presence of life processes is a fundamental criterion that can be used to decide whether something is alive or not.

3. What are outside raw materials used for by an organism?

Answer

Various outside raw materials used by an organism are as follows:
→ Food as source of supplying energy and materials.
→ Oxygen for breakdown of food to obtain energy.
→ Water for proper digestion of food and other functions inside the body.
The raw materials required by an organism will vary depending on the complexity of the organism and its environment.

4. What processes would you consider essential for maintaining life?

Answer

Life processes such as nutrition, respiration, transportation, excretion, etc. are essential for maintaining life.

Page No: 101
 
1. What are the differences between autotrophic nutrition and heterotrophic nutrition?

Answer

Autotrophic Nutrition Heterotrophic Nutrition
Food is synthesised from simple inorganic raw materials such as CO2 and water. Food is obtained directly or indirectly from autotrophs. This food is broken down with the help of enzymes.
Chlorophyll is required. Chlorophyll is not required.
Food is generally prepared during day time. Food can be obtained at all time.
All green plants and some bacteria have this type of nutrition. All animals and fungi have this type of nutrition.

2. Where do plants get each of the raw materials required for photosynthesis?

Answer

The following raw materials are required for photosynthesis:
→ Carbon Dioxide: Plants get CO2 from atmosphere through stomata.
→ Water: Plants absorb water from soil through roots and transport to leaves.
→ Sunlight: Sunlight, which is absorbed by the chlorophyll and other green parts of the plant.

3. What is the role of the acid in our stomach?

Answer

Following are the roles of acid in our stomach:
→ The hydrochloric acid present in our stomach dissolves bits of food and creates an acidic medium. In this acidic medium, enzyme pepsinogen is converted to pepsin, which is a protein-digesting enzyme.
→ It also kills many bacteria and other microorganisms that enter alongwith the food.

4. What is the function of digestive enzymes?

Answer

Digestive enzymes such as amylase, lipase, pepsin, trypsin, etc. help in the breaking down of complex food particles into simple ones. These simple particles can be easily absorbed by the blood and thus transported to all the cells of the body.

5. How is the small intestine designed to absorb digested food?

Answer

The small intestine has millions of tiny finger-like projections called villi. These villi increase the surface area for more efficient food absorption. Within these villi, many blood vessels are present that absorb the digested food and carry it to the bloodstream. From the bloodstream, the absorbed food is delivered to each and every cell of the body.
View of villus in small intestine
 
Page No: 105
 
1. What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?

Answer

Terrestrial organisms take up oxygen from the atmosphere whereas aquatic animals obtain oxygen from water. Air contains more O2 as compared to water. Since the content of O2 in air is high, the terrestrial animals do not have to breathe faster to get more oxygen. Therefore, unlike aquatic animals, terrestrial animals do not need adaptations for gaseous exchange.

2. What are the different ways in which glucose is oxidized to provide energy in various organisms?

Answer

At first glucose (6 carbon molecules) is broken in the cytoplasm of cells of all organisms. This process yields a 3 carbon molecule compound called pyruvate.
Further break down of pyruvate takes place in different manners in different organisms.
Breakdown of Glucose
 
→ Anaerobic Respiration: This process takes place in absence of oxygen, e.g. in yeast during fermentation. In this case, pyruvate is converted into ethanol and carbon dioxide.
→ Aerobic Respiration: In aerobic respiration, the breakdown of pyruvate takes place in presence of oxygen to give rise to 3 molecules of carbon dioxide and water. The release of energy in aerobic respiration is much more than anaerobic respiration.
 

→ Lack of Oxygen: Sometimes, when there is lack of oxygen, especially during vigorous activity, in our muscles, pyruvate is converted into lactic acid (3 carbon molecule compounds). Formation of lactic acid in muscles causes cramp.
 
3. How is oxygen and carbon dioxide transported in human beings?

Answer

→ Transport of Oxygen: The respiratory pigments (haemoglobin) present in red blood cells takes up the oxygen from the air to the lungs. They carry the oxygen to tissues which are deficient in oxygen.

→ Transport of carbon dioxide: Carbon Dioxide is more soluble in water. Hence, it is mostly transported from body tissues in the dissolved form in our blood plasma to lungs where it diffuses from blood to air in the lungs and then expelled out through nostrils.

4. How are the lungs designed in human beings to maximize the area for exchange of gases?

Answer

Lungs contain millions of alveoli which provide a surface for the exchange of gases. An extensive network of blood vessels is present in the wall of the alveoli. By lifting our ribs and flatten the diaphragm, the chest cavity becomes spacious. Air is sucked into the lungs and alveoli. The oxygen from the breath, diffuses into the blood and CO2 from the blood brought from the body, diffuses out into the air.

Page No: 110

1. What are the components of the transport system in human beings? What are the functions of these components?

Answer

The main components of the transport system in human beings are the heart, blood, and blood vessels.
→ Heart pumps oxygenated blood throughout the body. It receives deoxygenated blood from the various body parts and sends this impure blood to the lungs for oxygenation.
 

→ Blood helps in the transport of oxygen, nutrients, CO2, and nitrogenous wastes.
→ The blood vessels (arteries, veins, and capillaries) carry blood either away from the heart to various organs or from various organs back to the heart.

2. Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

Answer

It is necessary to separate oxygenated and deoxygenated blood to maintain efficient supply of oxygen into the body. This system is essential in animals that have high energy need. For example, animals like mammals and birds which constantly use this energy to maintain their body temperature.

3. What are the components of the transport system in highly organised plants?

Answer

In highly organised plants, there are two different types of conducting tissues – xylem and phloem. Xylem conducts water and minerals obtained from the soil (via roots) to the rest of the plant. Phloem transports food materials from the leaves to different parts of the plant body.

4. How are water and minerals transported in plants?

Answer

Water and minerals are transported through xylem cells from soil to the leaves. The xylem cells of roots stem and leaves are interconnected to form a conducting channel that reaches all parts of the plant. The root cells take ions from the soil. This creates a difference between the concentration of ions of roots and soil. Therefore, there is a steady movement of water into xylem. An osmotic pressure is formed and water and minerals are transported from one cell to the other cell due to osmosis. The continuous loss of water takes place due to transpiration. Because of transpiration, a suction pressure is created as a result of which water is forced into the xylem cells of roots. The effect of root pressure for transportation in plants is more important in night while during day time transpiration pull becomes the major driving force.
 
5. How is food transported in plants?

Answer

Phloem transports food materials from the leaves to different parts of the plant. The transportation of food in phloem is achieved by utilizing energy from ATP which helps in creating osmotic pressure that transport food from the area of high concentration to low concentration.

Page No: 112

1. Describe the structure and functioning of nephrons.

Answer

Nephrons are the basic filtering units of kidneys. Each kidney possesses large number of nephrons, approximately 1-1.5 million. The main components of the nephron are glomerulus, Bowman’s capsule, and a long renal tubule.
Structure of Nephron
 
Functioning of a nephron:
→ The blood enters the kidney through the renal artery, which branches into many capillaries associated with glomerulus.
→ The water and solute are transferred to the nephron at Bowman’s capsule.
 

→ In the proximal tubule, some substances such as amino acids, glucose, and salts are selectively reabsorbed and unwanted molecules are added in the urine.
→ The filtrate then moves down into the loop of Henle, where more water is absorbed.
→ From here, the filtrate moves upwards into the distal tubule and finally to the collecting duct. Collecting duct collects urine from many nephrons.
 
→ The urine formed in each kidney enters a long tube called ureter. From ureter, it gets transported to the urinary bladder and then into the urethra.
 
2. What are the methods used by plants to get rid of excretory products?

Answer

Plants can get rid of excess of water by transpiration. Waste materials may be stored in the cell vacuoles or as gum and resin, especially in old xylem. It is also stored in the leaves that later fall off.

3. How is the amount of urine produced regulated?

Answer

The amount of urine produced depends on the amount of excess water and dissolved wastes present in the body. Some other factors such as habitat of an organism and hormone such as Anti-diuretic hormone (ADH) also regulates the amount of urine produced.

Exercise

1. The kidneys in human beings are a part of the system for
(a) nutrition.

(b) respiration.
(c) excretion.
(d) transportation.

► (c) excretion.

2. The xylem in plants are responsible for
(a) transport of water.
(b) transport of food.
(c) transport of amino acids.
(d) transport of oxygen.
► (a) transport of water.

3. The autotrophic mode of nutrition requires
(a) carbon dioxide and water.
(b) chlorophyll.
(c) sunlight.
(d) all of the above.
► (d) all of the above.

4. The breakdown of pyruvate to give carbon dioxide, water and energy takes place in
(a) cytoplasm.
(b) mitochondria.
(c) chloroplast.
(d) nucleus.
► (b) mitochondria.

5. How are fats digested in our bodies? Where does this process take place?

Answer

Fats are present in the form of large globules in the small intestine. The small intestine receives the secretions from the liver and the pancreas. The bile salts (from the liver) break down the large fat globules into smaller globules so that the pancreatic enzyme lipase can easily act on them. This is referred to as emulsification of fats. This process takes place in the small intestine.

6. What is the role of saliva in the digestion of food?

Answer

The role of saliva in the digestion of food:
→ It moistens the food for easy swallowing.
→ It contains a digestive enzyme called salivary amylase, which breaks down starch into sugar.

7. What are the necessary conditions for autotrophic nutrition and what are its by-products?

Answer

Autotrophic nutrition takes place through the process of photosynthesis. Carbon dioxide, water, chlorophyll pigment, and sunlight are the necessary conditions required for autotrophic nutrition. Carbohydrates (food) and O2 are the by-products of photosynthesis.

8. What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.

Answer

Aerobic respiration Anaerobic respiration
It occurs in the presence of O2. It occurs in the absence of O2.
It involves the exchange of gases between the organism and the outside environment. Exchange of gases is absent.
It occurs in cytoplasm and mitochondria. It occurs only in cytoplasm.
It always releases CO2 and H2O. End products vary.

 

The organisms that use anaerobic mode of respiration include some bacteria and microorganisms such as yeast.
 


9. How are the alveoli designed to maximise the exchange of gases?

Answer

Alveoli provide a surface for the exchange of gases. An extensive network of blood vessels is present in the wall of the alveoli. By lifting our ribs and flatten the diaphragm, the chest cavity becomes spacious. Air is sucked into the lungs and alveoli. The oxygen from the breath, diffuses into the blood and CO2 from the blood brought from the body, diffuses out into the air.

10. What would be the consequences of a deficiency of haemoglobin in our bodies?

Answer

Haemoglobin is the respiratory pigment that transports oxygen to the body cells for cellular respiration. Therefore, deficiency of haemoglobin in blood can affect the oxygen supplying capacity of blood. This can lead to deficiency of oxygen in the body cells. It can also lead to a disease called anaemia.

11. Describe double circulation in human beings. Why is it necessary?

Answer

During a single cycle blood goes twice in the heart which is known as double circulation. It is necessary in human being to separate oxygenated and de-oxygenated blood because this makes their circulatory system is more efficient and helps in maintaining constant body temperature.

12. What are the differences between the transport of materials in xylem and phloem?

Answer

Xylem Phloem
Xylem tissue helps in the transport of water and minerals. Phloem tissue helps in the transport of food.
Water is transported upwards from roots to all other plant parts. Food is transported in both upward and downward directions.
Transport in xylem occurs with the help of simple physical forces such as transpiration pull. Transport of food in phloem requires energy in the form of ATP.


13. Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.

Answer

Alveoli Nephrons
Structure Structure
Alveoli are tiny balloon-like structures present inside the lungs. Nephrons are tubular structures present inside the kidneys.
The walls of the alveoli are one cell thick and it contains an extensive network of blood capillaries. Nephrons are made of glomerulus, bowman’s capsule, and a long renal tube.
Function Function
The exchange of O2 and CO2 takes place between the blood of the capillaries that surround the alveoli and the gases present in the alveoli. The blood enters the kidneys through the renal artery. The blood is entered here and the nitrogenous waste in the form of urine is collected by collecting duct.
Alveoli are the site of gaseous exchange. Nephrons are the basic filtration unit.

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Quick Revision Notes –Chapter 6 Life Processes  

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NCERT Solutions for Class 10 Science Chapter 5 Periodic Classification of Elements

NCERT Solutions for Class 10 Science Chapter 5 Periodic Classification of Elements

NCERT Solutions for Class 10 Science Chapter 5 Periodic Classification of Elements includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

 

Page No: 81

1. Did Dobereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.

Answer

Yes, Dobereiner’s triads also exist in the columns of Newlands’ Octaves. One such column is Li, K, Na.

2. What were the limitations of Dobereiner’s classification?

Answer

Limitation of Dobereiner’s classification:
All known elements could not be classified into groups of triads on the basis of their properties.

3. What were the limitations of Newlands’ Law of Octaves?

Answer

Limitations of Newlands’ law of octaves:
→ It was not applicable throughout the arrangements. It was applicable up to calcium only. The properties of the elements listed after calcium showed no resemblance to the properties of the elements above them.
→ Those elements that were discovered after Newlands’ octaves did not follow the law of octaves.
→ The position of cobalt and nickel in the group of the elements (F, Cl) of different properties could not be explained.
→ Placing of iron far away from cobalt and nickel, which have similar properties as iron, could also not be explained.

Page No: 85

1. Use Mendeleev’s Periodic Table to predict the formulae for the oxides of the following elements:
K, C, Al, Si, Ba.

Answer

K is in group 1. Therefore, the oxide will be K2O.
C is in group 4. Therefore, the oxide will be CO2.
Al is in group 3. Therefore, the oxide will be Al2O3.
Si is in group 4. Therefore, the oxide will be SiO2.
Ba is in group 2. Therefore, the oxide will be BaO.

2. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)

Answer

Scandium and germanium.

3. What were the criteria used by Mendeleev in creating his Periodic Table?

Answer

Mendeleev used atomic mass of the elements as the unique criteria of the elements. He proposed that the chemical properties of elements are the periodic function of their atomic masses. And thus, he arranged the elements in the increasing order of their atomic masses.

4. Why do you think the noble gases are placed in a separate group?

Answer

Noble gases are inert elements. Their properties are different from the all other elements. Therefore, the noble gases are placed in a separate group.

Page No: 90

1. How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table?

Answer

Various anomalies of Mendeleev’s Periodic Table removed as follows in the Modern Periodic Table:

→ Elements are arranged in the increasing order of their atomic number in Modern Periodic Table, thus there was no need for keeping more than one element in one slot.

→ In Modern Periodic Table there was no problem of the place of isotopes, as isotopes have same atomic mass with different atomic numbers.

→ Elements having same valence electron are kept in same group.

→ Elements having same number of shells were put under the same period.
→ Position of hydrogen became clarified in as it is kept in the group with the elements of same valence electrons.

2. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?

Answer

Calcium (Ca) and strontium (Sr) are expected to show chemical reactions similar to magnesium (Mg). This is because the number of valence electrons (2) is same in all these three elements and since chemical properties are due to valence electrons, they show same chemical reactions.

3. Name
(a) three elements that have a single electron in their outermost shells.
(b) two elements that have two electrons in their outermost shells.
(c) three elements with filled outermost shells.

Answer

(a) Lithium (Li), sodium (Na), and potassium (K) have a single electron in their outermost shells.
(b) Magnesium (Mg) and calcium (Ca) have two electrons in their outermost shells.
(c) Neon (Ne), argon (Ar), and xenon (Xe) have filled outermost shells.

4. (a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

Answer

(a) Yes. The atoms of all the three elements lithium, sodium, and potassium have one electron in their outermost shells.

(b) Both helium (He) and neon (Ne) have filled outermost shells. Helium has a duplet in its K shell, while neon has an octet in its L shell.

5. In the Modern Periodic Table, which are the metals among the first ten elements?

Answer

 

Among the first ten elements, lithium (Li) and beryllium (Be) are metals.

6. By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristic?

Answer

Since Be lies to the extreme left hand side of the periodic table, Be is the most metallic among the given elements.

Excercise

1. Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic Table.
(a) The elements become less metallic in nature.
(b) The number of valence electrons increases.
(c) The atoms lose their electrons more easily.
(d) The oxides become more acidic.
► (c) The atoms lose their electrons more easily.

2. Element X forms a chloride with the formula XCl2, which is a solid with a high melting point. X would most likely be in the same group of the Periodic Table as
(a) Na
(b) Mg
(c) Al 
(d) Si
► (b) Mg

3. Which element has
(a) two shells, both of which are completely filled with electrons?
(b) the electronic configuration 2, 8, 2?
(c) a total of three shells, with four electrons in its valence shell?
(d) a total of two shells, with three electrons in its valence shell?
(e) twice as many electrons in its second shell as in its first shell?

Answer

(a) Neon
(b) Magnesium
(c) Silicon
(d) Boron
(e) Carbon

4. (a) What property do all elements in the same column of the Periodic Table as boron have in common?
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?

Answer

(a) Valency equal to 3.
(b) Valency equal to 1.

5. An atom has electronic configuration 2, 8, 7.
(a) What is the atomic number of this element?
(b) To which of the following elements would it be chemically similar? (Atomic numbers are given in parentheses.)
N(7) F(9) P(15) Ar(18)

Answer

(a) The atomic number of this element is 17.
(b) It would be chemically similar to F(9) with configuration as 2, 7.

Page No: 92

6. The position of three elements A, B and C in the Periodic Table are shown below –
 
Group 16
Group 17
−
−
−
A
−
−
B
C

(a) State whether A is a metal or non-metal.
(b) State whether C is more reactive or less reactive than A.
(c) Will C be larger or smaller in size than B?
(d) Which type of ion, cation or anion, will be formed by element A?

Answer

(a) A is a non-metal.

(b) C is less reactive than A, as reactivity decreases down the group in halogens.

(c) C will be smaller in size than B as moving across a period, the nuclear charge increases and therefore, electrons come closer to the nucleus.
 

(d) A will form an anion as it accepts an electron to complete its octet.
 

7. Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?

Answer

Nitrogen (7): 2, 5
Phosphorus (15): 2, 8, 5
Since, electronegativity decreases with moving from top to bottom in a group, thus Nitrogen will be more electronegative.

8. How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?

Answer

In the modern periodic table, atoms with similar electronic configurations are placed in the same column. In a group, the number of valence electrons remains the same.
Elements across a period show an increase in the number of valence electrons.

9. In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21, and 38. Which of these have physical and chemical properties resembling calcium?

Answer

The element with atomic number 12 has same chemical properties as that of calcium. This is because both of them have same number of valence electrons (2).

10. Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table and the Modern Periodic Table.

Answer

Mendeleev’s periodic table Modern periodic table
Elements are arranged in the increasing order of their atomic masses. Elements are arranged in the increasing order of their atomic numbers.
There are 8 Groups. There are 18 Groups.
Each group are subdivided into subgroup ‘a’ and ‘b’
Groups are not subdivided into sub-groups.
Groups for Noble gas was not present as noble gases were not discovered by that time.
A separate group is meant for noble gases.
There was no place for isotopes.
This problem has been rectified as slots are determined according to atomic number.

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NCERT Solutions for Class 10 Science Chapter 4 Carbon and its Compounds

NCERT Solutions for Class 10 Science Chapter 4 Carbon and its Compounds

NCERT Solutions for Class 10 Science Chapter 4 Carbon and its Compounds includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

 

Page No: 61

1. What would be the electron dot structure of carbon dioxide which has the formula CO2?

Answer


2. What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (Hint – the eight atoms of sulphur are joined together in the form of a ring.)

Answer

 

Page No: 68


1. How many structural isomers can you draw for pentane?

Answer

Three structural isomers are possible for pentane.


2. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?

Answer

The two features of carbon that give rise to a large number of compounds are as follows:
→ Catenation – It is the ability to form bonds with other atoms of carbon.
→ Tetravalency – With the valency of four, carbon is capable of bonding with four other atoms.

3. What will be the formula and electron dot structure of cyclopentane?

Answer

The formula for cyclopentane is C5H10. Its electron dot structure is given below.


Page No: 69

4. Draw the structures for the following compounds.
(i) Ethanoic acid (ii) Bromopentane*
(iii) Butanone (iv) Hexanal
*Are structural isomers possible for bromopentane?

Answer

(ii) There are many structural isomers possible for bromopentane. Among them, the structures of three isomers are given.


5. How would you name the following compounds?


Answer

(i) Bromoethane
(ii) Methanal (formaldehyde)
(iii) Hexyne

Page No: 71

1. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?

Answer

CH3CH2OH + (Alkaline KMnO4) → CH3COOH
Since, in this reaction one oxygen is added to ethanol, hence it is an oxidation reaction.

2. A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?

Answer

2HC ≡ CH + 5O2 → 4CO2 + 2H2O + Heat
When ethyne is burnt in air, it gives a sooty flame. This is due to incomplete combustion caused by limited supply of air. However, if ethyne is burnt with oxygen, it gives a clean flame with temperature 3000°C because of complete combustion. This oxy-acetylene flame is used for welding. It is not possible to attain such a high temperature without mixing oxygen. This is the reason why a mixture of ethyne and air is not used.

Page No: 74

1. How would you distinguish experimentally between an alcohol and a carboxylic acid?

Answer

We can distinguish between an alcohol and a carboxylic acid on the basis of their reaction with carbonates and hydrogen carbonates. Acid reacts with carbonate and hydrogen carbonate to evolve CO2 gas that turns lime water milky.

Alcohols, on the other hand, do not react with carbonates and hydrogen carbonates.

2. What are oxidising agents?

Answer

Oxidising agents are the substances that gain electrons in redox reaction and whose oxidation number is reduced.

Page No: 76

1. Would you be able to check if water is hard by using a detergent?

Answer

Detergent gives lather with hard and soft water both, while a soap gives lather with soft water only. Thus, it is not possible to check if water is hard; by using a detergent.

2. People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?

Answer

A soap molecule has two parts namely hydrophobic and hydrophilic. With the help of these, it attaches to the grease or dirt particle and forms a cluster called micelle. These micelles remain suspended as a colloid. To remove these micelles, it is necessary to agitate clothes.

Exercise

1. Ethane, with the molecular formula C2H6 has
(a) 6 covalent bonds.
(b) 7 covalent bonds.
(c) 8 covalent bonds.
(d) 9 covalent bonds.
► (b) 7 covalent bonds.

2. Butanone is a four-carbon compound with the functional group
(a) carboxylic acid.
(b) aldehyde.
(c) ketone.
(d) alcohol.
► (c) ketone.

3. While cooking, if the bottom of the vessel is getting blackened on the outside, it means that
(a) the food is not cooked completely.
(b) the fuel is not burning completely.
(c) the fuel is wet.
(d) the fuel is burning completely.
► (b) the fuel is not burning completely.

4. Explain the nature of the covalent bond using the bond formation in CH3Cl.

Answer

The structure of CH3Cl is given below:
Carbon has four valence electrons. It shares 1 electron each with 3 hydrogen atoms and 1 electron with chlorine. The bond between C and Cl atoms is covalent but due to higher value of electro-negativity of Cl, the C–Cl bond is polar in nature.

5. Draw the electron dot structures for
(a) ethanoic acid.
(b) H2S.
(c) propanone.
(d) F2.

Answer


6. What is a homologous series? Explain with an example.

Answer

A homologous series is a series of carbon compounds that have different numbers of carbon atoms but contain the same functional group.

For example, methane, ethane, propane, butane, etc. are all part of the alkane homologous series. The general formula of this series is CnH2n+2.
Methane CH4
Ethane CH3CH3
Propane CH3CH2CH3
Butane CH3­CH2CH2CH3
It can be noticed that there is a difference of -CH2 unit between each successive compound.

7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?

Answer

Ethanol and Ethanoic acid be differentiated on the basis of their following properties:
→ Ethanol is a liquid at room temperature with a pleasant smell. Ethanoic acid has a melting point of 17°C. Since it is below the room temperature so, it freezes during winter. Moreover, ethanoic acid has a smell like vinegar.
→ Ethanol does not react with metal carbonates while, ethanoic acid reacts with metal carbonates to form salt, water and carbon dioxide. For example,
 
2CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2O
→ Ethanol does not react with NaOH while ethanoic acid reacts with NaOH to form sodium ethanoate and water. For example,
 

CH3COOH + NaOH → CH3COONa + H2O→ Ethanol is oxidized to give ethanoic acid in presence of acidified KMnO4 while, no reaction takes place with ethanoic acid in presence of acidified KMnO4.

8. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?

Answer

Soap molecule has two ends. One end is hydrophilic and another end is hydrophobic. When soap is dissolved in water and clothes are put in the soapy solution, soap molecules converge in a typical fashion to make a structure; called micelle. The hydrophobic ends of different molecules surround a particle of grease and make the micelle; which is a spherical structure. In this, the hydrophilic end is outside the sphere and hydrophobic end is towards the centre of the sphere. This is why micelle formation takes place when soap is added to water.
Since ethanol is not as polar as soap, so micelles will not be formed in other solvents such as ethanol.
 

9. Why are carbon and its compounds used as fuels for most applications?

Answer

Carbon and its compounds give large amount of heat on combustion due to high percentage of carbon and hydrogen. Carbon compounds used as fuel have optimum ignition temperature with high calorific values and are easy to handle. Their combustion can e controlled. Therefore, carbon and its compounds are used as fuels.

10. Explain the formation of scum when hard water is treated with soap.

Answer

Hard water often contains salts of calcium and magnesium. Soap molecules react with the salts of calcium and magnesium and form a precipitate. This precipitate begins floating as an off-white layer over water. This layer is called scum. Soaps lose their cleansing property in hard water because of formation of scum.

11. What change will you observe if you test soap with litmus paper (red and blue)?

Answer

Since soap is basic in nature, it will turn red litmus blue. However, the colour of blue litmus will remain blue.

12. What is hydrogenation? What is its industrial application?

Answer

Hydrogenation is the chemical reaction between hydrogen and other compounds in the presence of catalyst. Hydrogenation is used mainly to reduce saturated hydrocarbons. Hydrogenation is an addition reaction.For Example: When ethene is heated with the catalyst nickel it is reduced to ethane.
Industrial application:
→ >Hydrogenation is used in many industrial applications. For example; in Petrochemical Industry, hydrogenation is used to convert alkenes into alkanes (paraffins) and cycloalkanes.
→ It is also used to prepare vegetable ghee from vegetable oils.
 


13. Which of the following hydrocarbons undergo addition reactions:
C2, H6, C3H8, C3H6, C2H2 and CH4.

Answer

Unsaturated hydrocarbons undergo addition reactions. Being unsaturated hydrocarbons, C3H6 and C2H2 undergo addition reactions.

14. Give a test that can be used to differentiate chemically between butter and cooking oil.

Answer

Butter contains saturated fats. Therefore, it cannot be hydrogenated. On the other hand, oil has unsaturated fats. That is why it can be hydrogenated to saturated fats (solids).

15. Explain the mechanism of the cleaning action of soaps.
 
Answer
 
The dirt present on clothes is organic in nature and insoluble in water. Therefore, it cannot be removed by only washing with water. When soap is dissolved in water, its hydrophobic ends attach themselves to the dirt and remove it from the cloth. Then, the molecules of soap arrange themselves in micelle formation and trap the dirt at the centre of the cluster. These micelles remain suspended in the water. Hence, the dust particles are easily rinsed away by water.
Cleansing action of soaps

Important Links

Quick Revision Notes –Chapter 4 Carbon and its Compounds  

Most Important Questions-Chapter 4 Carbon and its Compounds  

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NCERT Solutions for Class 10 Science Chapter 3 Metals and Non Metals

NCERT Solutions for Class 10 Science Chapter 3 Metals and Non Metals

NCERT Solutions for Class 10 Science Chapter 3 Metals and Non Metals includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

 

Page No: 40

1. Give an example of a metal which
(i) is a liquid at room temperature.

► Mercury

(ii) can be easily cut with a knife.
► Sodium

(iii) is the best conductor of heat.

► Silver

 
(iv) is a poor conductor of heat.
► Mercury and Lead
 

2.Explain the meanings of malleable and ductile.

Answer

Malleable:Substances that can be beaten into thin sheets are called malleable. For example, most of the metals are malleable.
Ductile: Substances that can be drawn into thin wires are called ductile. For example, most of the metals are ductile.

 
Page no: 46
 

1. Why is sodium kept immersed in kerosene oil?

Answer

Sodium is high reactive element. If it is kept in open it can explosively react with oxygen to catch fire. Hence to prevent accidental damage sodium is immersed in kerosene oil.

2. Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water

Answer

(i) 3Fe (s) + 4H2O (g) → Fe3O4 (aq) + 4H2 (g)

(ii) Ca (s) + 2H2O (l) → Ca(OH)2 (aq) + H2 (g) + Heat
2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g) + Heat

3. Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows.

Metal
Iron (II) sulphate
Cooper (II) sulphate
Zinc sulphate
Silver nitrate
A.
No reaction
Displacement
    
B.
Displacement
  
No reaction
  
C.
No reaction
No reaction
No reaction
Displacement
D.
No reaction
No reaction
No reaction
No reaction


Use the Table above to answer the following questions about metals A, B, C and D.
(i) Which is the most reactive metal?
(ii) What would you observe if B is added to a solution of copper (II) sulphate?
(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.

Answer

(i) B is most reactive metal.
(ii) B will displace copper from copper sulphate.
(iii) Arrangement of metals in the order of decreasing reactivity B>A>C>D.

4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.

Answer

Hydrogen gas is evolved when dilute hydrochloric acid is added to a reactive metal.

When iron reacts with dilute H2SO4, iron (II) sulphate with the evolution of hydrogen gas is formed.
Fe (s) + H2SO4 (aq) → FeSO4 (aq) + H2 (g)

5. What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.


Answer

When zinc is added to iron (II) sulphate then it will displace the iron from iron sulphate solution as shown in the following chemical reaction.Zn (s) + FeSO4 (aq) → ZnSO4 (aq) + Fe (s)

Page No: 49

1. (i) Write the electron-dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of Na2O and MgO by the transfer of electrons.
(iii) What are the ions present in these compounds?

Answer

(i) The representation of elements with valence electrons as dots around the elements is referred to as electron-dot structure for elements.


(ii)


(iii) The ions present in Na2O are Na+ and O2– ions and in MgO are Mg2+ and O2– ions.

2. Why do ionic compounds have high melting points?

Answer

Ionic compounds have strong electrostatic forces of attraction between the ions. Therefore, it requires a lot of energy to overcome these forces. That is why ionic compounds have high melting points.

 
Page No: 53
 
1. Define the following terms.
(i) Mineral (ii) Ore (iii) Gangue
 
Answer
 

(i) Mineral: The naturally occurring compounds of elements are known as Mineral.
(ii) Ore: Minerals from which metals can be extracted profitably are known as ores.
(iii) Gangue: The impurities present in the ore such as sand, rocks etc are non as gangue.

2. Name two metals which are found in nature in the free state.

Answer

The metals at the bottom of the reactivity series are mostly found in free state. For example: gold, silver, and platinum.

3. What chemical process is used for obtaining a metal from its oxide?

Answer

A metal can be extracted from its oxide by the process of reduction.


Page No: 55

1. Metallic oxides of zinc, magnesium and copper were heated with the following metals.

Metal
Zinc
Magnesium
Copper
Zinc oxide
–
–
–
Magnesium oxide
–
–
–
Copper oxide
–
–
–


In which cases will you find displacement reactions taking place?

Answer

Metal
Zinc
Magnesium
Copper
Zinc oxide
No reaction
Displacement
No reaction
Magnesium oxide
No reaction
No reaction
No reaction
Copper oxide
Displacement
Displacement
No reaction


2. Which metals do not corrode easily?

Answer

Metals which have low reactivity such as silver, gold does not corrode easily.

3. What are alloys?

Answer

An alloy is the homogeneous mixture of two or more metals or metals and non metals. For example brass is an alloy of copper and zinc.

Excercise

1. Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) MgCl2solution and aluminium metal
(c) FeSO4solution and silver metal
(d) AgNO3solution and copper metal.
► (d) AgNO3solution and copper metal.

2. Which of the following methods is suitable for preventing an iron frying pan from rusting?
(a) Applying grease
(b) Applying paint
(c) Applying a coating of zinc
(d) all of the above.
► (c) Applying a coating of zinc

3. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be
(a) calcium
(b) carbon
(c) silicon
(d) iron
► (a) calcium

4. Food cans are coated with tin and not with zinc because
(a) zinc is costlier than tin.
(b) zinc has a higher melting point than tin.
(c) zinc is more reactive than tin.
(d) zinc is less reactive than tin.
► (c) zinc is more reactive than tin.

5. You are given a hammer, a battery, a bulb, wires and a switch.
(a) How could you use them to distinguish between samples of metals and non-metals?
 
(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.
Anwer

(a) With the hammer, we can beat the sample and if it can be beaten into thin sheets (that is, it is malleable), then it is a metal otherwise a non-metal. Similarly, we can use the battery, bulb, wires, and a switch to set up a circuit with the sample. If the sample conducts electricity, then it is a metal otherwise a non-metal.

(b) The above tests are useful in distinguishing between metals and non-metals as these are based on the physical properties. No chemical reactions are involved in these tests.
 

 
6. What are amphoteric oxides? Give two examples of amphoteric oxides.

Answer
 
Those oxides that behave as both acidic and basic oxides are called amphoteric oxides.
Examples: aluminium oxide (Al2O3), zinc oxide (ZnO)
 

7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

Answer

Iron and aluminium will displace hydrogen from dilute acids as they more reactive then hydrogen. Mercury and copper cannot displace hydrogen from dilute acids as they are less reactive than hydrogen.

Page No: 57

8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?

Answer

In the electrolytic refining of a metal M:
Anode → Impure metal M
Cathode → Thin strip of pure metal M
Electrolyte → Solution of salt of the metal M
 
9. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below.
(a) What will be the action of gas on
(i) dry litmus paper?
(ii) moist litmus paper?


(b) Write a balanced chemical equation for the reaction taking place.

Answer

(a)
(i) There will be no action on dry litmus paper.

(ii) The colour of litmus paper will turn red because sulphur is a non-metal and the oxides of non-metal are acidic in nature.

(b) S (s) + O2(g) → SO2 (g)

10. State two ways to prevent the rusting of iron.

Answer

Two ways to prevent the rusting of iron are:
→ Oiling, greasing, or painting: By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. Hence, rusting is prevented.
→ Galvanisation:An iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.
 

11. What type of oxides are formed when non-metals combine with oxygen?

Answer

When non-metals are combined with oxygen then neutral or acidic oxides are formed. Examples of acidic oxides are NO2, SO2 and examples of neutral oxides are NO, CO etc.

12. Give reasons

(a) Platinum, gold and silver are used to make jewellery.
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.

Answer

(a) Platinum, gold, and silver are used to make jewellery because they are very lustrous. Also, they are very less reactive and do not corrode easily.

(b) Sodium, potassium, and lithium are very reactive metals and react very vigorously with air as well as water.Therefore, they are kept immersed in kerosene oil in order to prevent their contact with air and moisture.
 

(c) Though aluminium is a highly reactive metal, it is resistant to corrosion. This is because aluminium reacts with oxygen present in air to form a thin layer of aluminium oxide. This oxide layer is very stable and prevents further reaction of aluminium with oxygen. Also, it is light in weight and a good conductor of heat. Hence, it is used to make cooking utensils.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because metals can be easily extracted from their oxides rather than from their carbonates and sulphides.

13. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Answer

Copper reacts with moist carbon dioxide in air to form copper carbonate and as a result, copper vessel loses its shiny brown surface forming a green layer of copper carbonate. The citric acid present in the lemon or tamarind neutralises the basis copper carbonate and dissolves the layer. That is why, tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its characteristic lustre.

14. Differentiate between metal and non-metal on the basis of their chemical properties.

Answer

Metal
Non-metal
Metals are electropositive. Non-metals are electronegative.
Oxides of metal are basic in nature. Oxides of non-metals are acidic in nature.
Metals displace hydrogen from dilute acids. They can’t replace hydrogen from dilute acids.
Metals form chlorides which are electrovalent or ionic compounds. Non-metals form chlorides which are covalent compounds.
They react with water to form oxides and hydroxides. Some metals react with cold water, some with hot water, and some with steam. They do not react with water.

15. A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?

Answer

The solution he had used was Aqua regia. Aqua regia is Latin word which means ‘Royal Water’. It is the mixture of concentrated Hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It is capable of dissolving metals like Gold and Platinum. Since the outer layer of the gold bangles is dissolved in aqua regia so their weight was reduced drastically.

16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).

Answer

Copper does not react with cold water, hot water, or steam. However, iron reacts with steam. If the hot water tanks are made of steel (an alloy of iron), then iron would react vigorously with the steam formed from hot water. 3Fe + 4H2O → Fe3O4 + H2O
That is why copper is used to make hot water tanks, and not steel.

Important Links

Quick Revision Notes –Chapter 3 Metals and Non Metals

Most Important Questions-Chapter 3 Metals and Non Metals

Important MCQs- Chapter 3 Metals and Non Metals

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NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

 

Page No: 18

1. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

Answer

If the colour of red litmus does not change then it is acid. If the colour of red litmus changes to blue then it is base. If there is slight change in the colour of red litmus (such as purple) then it is distilled water.

Page No: 22

1. Why should curd and sour substances not be kept in brass and copper vessels?

Answer

Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products, thereby spoiling the food.

2. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?

Answer

Hydrogen gas is usually liberated when an acid reacts with metal.

 
Take few pieces of zinc granules and add 5 ml of dilute H2SO4. Shake it and pass the gas produced into a soap solution. The bubbles of the soap solution are formed. These soap bubbles contain hydrogen gas.
H2SO4 + Zn → ZnSO4 + H2 ↑
We can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the soap bubbles.

3. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

Answer

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l)
Calcium Carbonate + Hydrochloric acid → Calcium Chloride + Carbon dioxide + Water

Page No: 25

1. Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

Answer

When HCl or HNO3 are mixed with water then they dissolve in water to form H+ or H3O+ ions which shows their acidic character. For example just see the following reactions
HCl (aq) → H+ + Cl–
H+ + H2O → H3O+
When alcohols and glucose are mixed with water then they do not dissolve to form ions. Hence they do not show acidic character.

2. Why does an aqueous solution of an acid conduct electricity?

Answer

The presence of hydrogen (H+) or hydronium (H3O+) ions in the aqueous solution of an acid are responsible for conducting electricity.

3. Why does dry HCl gas not change the colour of the dry litmus paper?

Answer

Dry HCl gas not change the colour of the dry litmus paper because it has no Hydrogen ions (H+) in it.

4. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
 
Answer
 
Since the process of dissolving an acid in water is exothermic, it is always recommended that acid should be added to water. If it is done the other way, then it is possible that because of the large amount of heat generated, the mixture splashes out and causes burns.

5. How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?

Answer

When an acid is diluted, the concentration of hydronium ions (H3O+) per unit volume decreases. This means that the strength of the acid decreases.

6. How is the concentration of hydroxide ions (OH−) affected when excess base is dissolved in a solution of sodium hydroxide?

Answer

The concentration of hydroxide ions (OH−) would increase when excess base is dissolved in a solution of sodium hydroxide.

Page No: 28

1. You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?

Answer

A pH value of less than 7 indicates an acidic solution, while greater than 7 indicates a basic solution. Therefore, the solution with pH = 6 is acidic and has more hydrogen ion concentration than the solution of pH = 8 which is basic.

2. What effect does the concentration of H+ (aq) ions have on the nature of the solution?

Answer

If the concentration of H+ (aq) ions is increased (>10-7) then the solution become acidic and if the concentration of H+ (aq) ions is decreased (<10-7) then the solution become basic in nature.

3. Do basic solutions also have H+ (aq) ions? If yes, then why are these basic?

Answer

Yes, basic solution also has H+ ions. However, their concentration is less as compared to the concentration of OH– ions that makes the solution basic.

4. Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?

Answer

If the soil is acidic and improper for cultivation, then to increase the basicity of soil, the farmer would treat the soil with quick lime or slaked lime or chalk.

Page No: 33

1. What is the common name of the compound CaOCl2?
► Bleaching Powder.

2. Name the substance which on treatment with chlorine yields bleaching powder?
► Calcium hydroxide [Ca(OH)2]

3. Name the sodium compound which is used for softening hard water.
► Washing soda (Na2CO3.10H2O)

4. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.

Answer

When sodium hydrogen carbonate is heated then sodium carbonate and water is formed along with the evolution of carbon dioxide gas.

5. Write an equation to show the reaction between Plaster of Paris and water.

Answer

Exercise

1. A solution turns red litmus blue, its pH is likely to be
(a) 1
(b) 4
(c) 5
(d) 10
► (d) 10

2. A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains
(a) NaCl
(b) HCl 
(c) LiCl 
(d) KCl
► (b) HCl

3. 10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralise it will be
(a) 4 mL
(b) 8mL
(c) 12 mL 
(d) 16 mL
► (d) 16 mL

4. Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic
► (c) Antacid

5, Write word equations and then balanced equations for the reaction taking place when −
(a) dilute sulphuric acid reacts with zinc granules.
 
(b) dilute hydrochloric acid reacts with magnesium ribbon.
 
(c) dilute sulphuric acid reacts with aluminium powder.
 
(d) dilute hydrochloric acid reacts with iron filings.

Answer

(a) H2SO4 (aq) + Zn (s) → ZnSO4 (aq) + H2 (g)

(b) 2HCl (aq) + Mg (s) → MgCl2 (aq) + H2 (g)

(c) 3H2SO4 (aq) + 2Al (s) → Al2(SO4)3 (aq) + 3H2 (g)

(d) 6HCl (aq) + 2Fe (s) → 2FeCl3 (aq) + 3H2 (g)

6. Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an activity to prove it.

Answer

Two nails are fitted on a cork and are kept it in a 100 mL beaker. The nails are then connected to the two terminals of a 6-volt battery through a bulb and a switch. Some dilute HCl is poured in the beaker and the current is switched on. The same experiment is then performed with glucose solution and alcohol solution.

Observations:
It will be observed that the bulb glows in the HCl solution and does not glow in the glucose solution.

Result:
HCl dissociates into H+and Cl−ions. These ions conduct electricity in the solution resulting in the glowing of the bulb. On the other hand, the glucose solution does not dissociate into ions. Therefore, it does not conduct electricity.


Conclusion:
From this activity, it can be concluded that all acids contain hydrogen but not all compounds containing hydrogen are acids.
That is why, though alcohols and glucose contain hydrogen, they are not categorised as acids.
 

7. Why does distilled water not conduct electricity, whereas rain water does?

Answer

Distilled water cannot conduct electricity because it does not contain ions while rain water conducts electricity as it contains ions due presence of dissolved salts in it.

8. Why do acids not show acidic behaviour in the absence of water?

Answer

Acids do not show acidic behaviour in the absence of water because the dissociation of hydrogen ions from an acid occurs in the presence of water only.

9. Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is
(a) neutral?
(b) strongly alkaline?
(c) strongly acidic?
(d) weakly acidic?
(e) weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.

Answer

(a) Neutral →Solution D with pH 7
(b) Strongly alkaline →Solution C with pH 11
(c) Strongly acidic →Solution B with pH 1
(d) Weakly acidic →Solution A with pH 4
(e) Weakly alkaline →Solution E with pH 9
The pH can be arranged in the increasing order of the concentration of hydrogen ions as: 11 < 9 < 7 < 4 < 1.

10. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why?

Answer

The fizzing will occur strongly in test tube A, in which hydrochloric acid (HCl) is added. This is because HCl is a stronger acid than CH3COOH and therefore produces hydrogen gas at a faster speed due to which fizzing occurs.

11. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.

Answer

The pH of milk is 6. As it changes to curd, the pH will reduce because curd is acidic in nature. The acids present in it decrease the pH.

12.A milkman adds a very small amount of baking soda to fresh milk.
 

(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
(b) Why does this milk take a long time to set as curd?
 
Answer
 
(a) The milkman shifts the pH of the fresh milk from 6 to slightly alkaline because in alkaline condition, milk does not set as curd easily.

(b) Since this milk is slightly basic than usual milk, acids produced to set the curd are neutralized by the base. Therefore, it takes a longer time for the curd to set.

13. Plaster of Paris should be stored in a moisture-proof container. Explain why?

Answer

The Plaster of Paris should be stored in a moisture-proof container as it absorbs water from moisture and turn into hard substance (Gypsum) as shown in following chemical equation.
 
14. What is a neutralization reaction? Give two examples.

Answer

A reaction in which an acid and base react with each other to give a salt and water is termed as neutralization reaction.For Example:
(i) NaOH + HCl → NaCl + H2O
(ii) HNO3 + KOH → KNO3 + H2O

15. Give two important uses of washing soda and baking soda.

Answer

Two important uses of washing soda are:
→ It is used in glass, soap, and paper industries.
→ It is used to remove permanent hardness of water.

Two important uses of baking soda are:
→ It is used as baking powder. Baking powder is a mixture of baking soda and a mild acid known as tartaric acid. When it is heated or mixed in water, it releases CO2 that makes bread or cake fluffy.
→ It is used in soda-acid fire extinguishers.

Important Links

Quick Revision Notes -Chapter 2 Acids, Bases and Salts

Most Important Questions-Chapter 2 Acids, Bases and Salts

Important MCQs- Chapter 2 Acids, Bases and Salts

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NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

 

NCERT Solutions for Class 10 Science Chapter 1 Intext Questions

(Page No. 6)

Question 1: Why should a magnesium ribbon be cleaned before burning in air?

Answer: A magnesium ribbon should be cleaned before burning because it is a reactive metal that reacts with oxygen from the air to form a stable, protective layer of magnesium oxide (MgO) on its surface. This layer prevents the magnesium underneath from burning properly. Cleaning the ribbon with sandpaper removes this oxide layer, allowing the pure magnesium to react with oxygen when heated.

Question 2: Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen

Answer:
(i) H₂(g) + Cl₂(g) → 2HCl(g)

(ii) 3BaCl₂(aq) + Al₂(SO₄)₃(aq) → 3BaSO₄(s) + 2AlCl₃(aq)

(iii) 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

Question 3: Write a balanced chemical equation with state symbols for the following reactions.
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

Answer:
(i) BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)
(Note: This is a precipitation reaction.)

(ii) NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
(Note: This is a neutralization reaction.)

(Page No. 10)

Question 1: A solution of a substance ‘X’ is used for whitewashing. (i) Name the substance ‘X’ and write its formula. (ii) Write the reaction of the substance ‘X’ named in (i) above with water.

Answer:
(i) The substance ‘X’ used for whitewashing is Calcium Oxide, also known as quicklime. Its chemical formula is CaO.

(ii) When calcium oxide (CaO) reacts with water (H₂O), it forms calcium hydroxide (Ca(OH)₂), also known as slaked lime. This reaction is highly exothermic, releasing a large amount of heat.

Chemical Equation:
CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat
(Quicklime) + (Water) → (Slaked Lime)

Question 2: Why is the amount of gas collected in one of the test tubes in Activity 1.7 (electrolysis of water) double of the amount collected in the other? Name this gas.

Answer:
In the electrolysis of water (H₂O), water decomposes into hydrogen gas (H₂) and oxygen gas (O₂). The balanced chemical equation for this reaction is:
2H₂O(l) →Electrolysis 2H₂(g) + O₂(g)

From the equation, we can see that two molecules of water produce two molecules of hydrogen gas and only one molecule of oxygen gas. This means the mole ratio of hydrogen to oxygen is 2:1.

Therefore, the volume of gas collected at the cathode (hydrogen) is double the volume of gas collected at the anode (oxygen).

The gas collected in double the amount is **Hydrogen gas (H₂)
**.

(Page No. 13)

Question 1: Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Answer:
When an iron nail is dipped in a copper sulphate solution, a displacement reaction occurs. Iron (Fe) is more reactive than copper (Cu). Therefore, iron displaces copper from the copper sulphate (CuSO₄) solution.

The blue colour of the copper sulphate solution fades and turns light green due to the formation of iron(II) sulphate (FeSO₄). A reddish-brown coating of copper metal is deposited on the iron nail.

Chemical Equation:
Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
(Iron) + (Blue solution) → (Light green solution) + (Brown deposit)

Question 2: Give an example of a double displacement reaction other than the one given in Activity 1.10.

Answer:
An example of a double displacement reaction is the reaction between silver nitrate (AgNO₃) and sodium chloride (NaCl). When their aqueous solutions are mixed, a white precipitate of silver chloride (AgCl) is formed along with a solution of sodium nitrate (NaNO₃).

Chemical Equation:
AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
(Silver Nitrate) + (Sodium Chloride) → (Silver Chloride – white ppt) + (Sodium Nitrate)

Question 3: Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(i) 4Na(s) + O₂(g) → 2Na₂O(s)
(ii) CuO(s) + H₂(g) → Cu(s) + H₂O(l)

Answer:

  • Oxidation: Gain of oxygen or loss of hydrogen.
  • Reduction: Loss of oxygen or gain of hydrogen.

(i) 4Na(s) + O₂(g) → 2Na₂O(s)

  • Sodium (Na) is gaining oxygen to form Sodium Oxide (Na₂O). Therefore, Sodium (Na) is oxidised.
  • Oxygen (O₂) is being combined with sodium. Therefore, Oxygen (O₂) is reduced.

(ii) CuO(s) + H₂(g) → Cu(s) + H₂O(l)

  • Copper Oxide (CuO) is losing oxygen to form Copper (Cu). Therefore, CuO is reduced.
  • Hydrogen (H₂) is gaining oxygen to form Water (H₂O). Therefore, H₂ is oxidised.

NCERT Solutions for Class 10 Science Chapter 1 Exercise Questions

Exercises

Page No: 14

1. Which of the statements about the reaction below are incorrect?
2PbO (s) + C (s) → 2Pb (s) + CO2 (g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.

(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all
► (i) (a) and (b)

2. Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.
► (d) displacement reaction.

Page No: 15

3. What happens when dilute hydrochloric acid is added to iron filings? Tick the correct answer.
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
► (a) Hydrogen gas and iron chloride are produced.

4. What is a balanced chemical equation? Why should chemical equations be balanced?

Answer

A reaction which has an equal number of atoms of all the elements on both sides of the chemical equation is called a balanced chemical equation.Chemical reaction should be balanced to follow law of conservation of mass.

5. Translate the following statements into chemical equations and then balance them.

(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Answer

(a) 3H2 (g) + N2 (g) → 2NH3 (g)

(b) 2H2S (g) + 3O2 (g) → 2H2O (l) + 2SO2 (g)

(c) 3BaCl2 (aq) + Al2(SO4)3 (aq) → 2AlCl3 (aq) + 3BaSO4 (s)

(d) 2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)

6. Balance the following chemical equations.

(i) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
(ii) NaOH + H2SO4 → Na2SO4 + H2O
(iii) NaCl + AgNO3 → AgCl + NaNO3
(iv) BaCl2 + H2SO4 → BaSO4 + HCl

Answer

(i) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(ii) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(iii) NaCl + AgNO3 → AgCl + NaNO3
(iv) BaCl2 + H2SO4 → BaSO4 + 2HCl

7. Write the balanced chemical equations for the following reactions.

(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
(c) Aluminium + Copper chloride → Aluminium chloride + Copper
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

Answer

(a) Ca(OH)2 + CO2 → CaCO3 + H2O

(b) Zn + 2AgNO3 → Zn(NO3)2 + 2Ag

(c) 2Al + 3CuCl2 → 2AlCl3 + 3Cu

(d) BaCl2 + K2SO4 → BaSO4 + 2KCl

8. Write the balanced chemical equation for the following and identify the type of reaction in each case.

(a)Potassium bromide (aq) + Barium iodide (aq)­ → Potassium iodide (aq) + Barium bromide(s)
(b) Zinc carbonate (s) → Zinc oxide (s) + Carbon dioxide (g)
(c) Hydrogen (g) + Chlorine (g) → Hydrogen chloride (g)
(d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g)


Answer
 
(a) 2KBr (aq) + BaI2 (aq) → 2KI (aq) + BaBr2 (s): Double displacement reaction
 
(b) ZnCO3 (s) →  ZnO (s) + CO2 (g): Decomposition reaction

(c) H2 (g) + Cl2 (g) → 2HCl (g): Combination reaction
 


(d) Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g) : Displacement Reaction

9. What does one mean by exothermic and endothermic reactions? Give examples.

Answer

Chemical reactions that release energy in the form of heat, light, or sound are called exothermic reactions.
Example: C (g) + O2 (g) → CO2 + Heat Energy

Reactions that absorb energy or require energy in order to proceed are called endothermic reactions.
Example:

10. Why is respiration considered an exothermic reaction? Explain.
 
Answer
 
Respiration is considered as an exothermic reaction because in respiration oxidation of glucose takes place which produces large amount of heat energy.
C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O (l) + Energy
 


11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

Answer

Decomposition reactions are those in which a compound breaks down to form two or more substances. These reactions require a source of energy to proceed. Thus, they are the exact opposite of combination reactions in which two or more substances combine to give a new substance with the release of energy.For Example:
Decomposition Reaction:
Combination Reaction:
CaO (s) + H2O (l) → Ca(OH)2 (aq)

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12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
 
Answer
 

13. What is the difference between displacement and double displacement reactions? Write equations for these reactions.

Answer

In a displacement reaction, a more reactive element replaces a less reactive element from a compound.
For Example: CuSo4 (aq) + Zn (s) → ZnSO4 (aq) + Cu (s)
 

In a double displacement reaction, two atoms or a group of atoms switch places to form new compounds.
For Example: Na2SO4 (aq) + BaCl2 (aq) → BaSO4 (s) + 2NaCl (aq)
 
14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

Answer

2AgNO3 (aq) + Cu (s) → Cu(NO3)2 (aq) + 2Ag (s)
Silver Nitrate + Copper → Copper Nitrate + Silver

15. What do you mean by a precipitation reaction? Explain by giving examples.

Answer

A reaction in which an insoluble solid (called precipitate) is formed is called a precipitation reaction.For Example:
Na2CO3 (aq) + CaCl2 (aq) → CaCO3 (s) + 2NaCl (aq)
 

Sodium Carbonate + Calcium Chloride → Calcium Carbonate + Sodium Chloride
In this reaction, calcium carbonate is obtained as a precipitate. Hence, it is a precipitation reaction.

16. Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction

Answer

Oxidation Reaction: It is a chemical reaction in which gain of oxygen or loss of hydrogen takes place.
Reduction Reaction: It is a chemical reaction in which loss of oxygen or gain of hydrogen takes place.

17. A shiny brown-coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.

Answer

‘X’ is copper (Cu) and the black-coloured compound formed is copper oxide (CuO). The equation of the reaction involved on heating copper is given below.

18. Why do we apply paint on iron articles?
Answer

Iron articles are painted because it prevents them from rusting. When painted, the contact of iron articles from moisture and air is cut off. Hence, rusting is prevented.

19. Oil and fat containing food items are flushed with nitrogen. Why?

Answer

Oil and fat containing food items flushed with nitrogen because nitrogen acts as an antioxidant and it prevents them from being oxidised.

20. Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity

Answer

Corrosion is defined as a process where materials, usually metals, deteriorate as a result of a chemical reaction with air, moisture, chemicals, etc.
For example, iron, in the presence of moisture, reacts with oxygen to form hydrated iron oxide.
4Fe + 3O2 + nH2O → 2Fe2O3.nH2O

Rancidity is the process of oxidation of fats and oils that can be easily noticed by the change in taste and smell is known as rancidity.
For example, the taste and smell of butter changes when kept for long.
 

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