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.
Page Number: 6
Question 1: Why should a magnesium ribbon be cleaned before burning in air?
Answer 1: Magnesium is a very reactive metal like (Na, Ca, etc.). When it exposed to air it reacts with oxygen to form a layer magnesium oxide (MgO) on its surface. This layer of magnesium oxide is quite stable and prevents further reaction of magnesium with oxygen. The magnesium ribbon is cleaned by sandpaper to remove this layer so that the underlying metal can be used for the reaction.
The Reaction involved in this case is as follows:
Question 2: Write the balanced equations for the following chemical reactions.
i) Hydrogen + Chloride → Hydrogen chloride
ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
iii) Sodium + Water → Sodium hydroxide + Hydrogen
Answer:
i) H2 + Cl2 → 2HCl
ii) 3BaCl2 + Al2(SO4)3 → 2AlCl3 + 3BaSO4
iii) 2Na + 2H2O → 2NaOH + H2
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 + Na2SO4 → BaSO4 + 2NaCl
(ii) NaOH + HCl → NaCl + H2O
Page no. 10
Question 1: A solution of a substance ‘X’ is used for white washing.
(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’ is calcium oxide. Its chemical formula is CaO.
(ii) Calcium oxide reacts vigorously with water to form calcium hydroxide (slaked lime)
CaO + H2O → Ca(OH)2
Question 2: Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.
Answer: Using the Electrolysis of water, hydrogen and oxygen are get separated by the electricity. Water (H2O) contains two parts hydrogen and one parts oxygen. Since hydrogen goes to one test tube and oxygen goes to another, the amount of gas collected in one of the test tubes is double of the amount collected in the other.
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, iron (which is more reactive than copper) displaces copper from copper sulphate solution forming iron sulphate, which is green in colour. Therefore, the blue colour of copper sulphate solution fades and green colour appears.
Question 2: Give an example of a double displacement reaction other than the one given in Activity 1.10.
Answer 2: Sodium carbonate reacts with calcium chloride to form calcium carbonate and sodium chloride.
In this reaction, sodium carbonate and calcium chloride exchange ions to form two new compounds. Hence, it is a double displacement reaction.
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 3: (i) Sodium (Na) is oxidized as it gains oxygen and oxygen gets reduced.
(ii) Copper oxide (CuO) is reduced to copper (Cu) while hydrogen (H2) gets oxidized to water (H2O)
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.
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.
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
(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.
Reactions that absorb energy or require energy in order to proceed are called endothermic reactions.
10. Why is respiration considered an exothermic reaction? Explain.
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:
CaO (s) + H2O (l) → Ca(OH)2 (aq)
Page No: 16
12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
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.
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.
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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