CLASS 10 CBSE CHEMISTRY PRACTICAL

EXPERIMENT: Study of the Comparative Cleaning Capacity of a Sample of Soap in Soft and Hard Water

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AIM:

To study the comparative cleaning capacity of a sample of soap in soft water and hard water.

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MATERIALS REQUIRED:

S. No.	Material	Quantity
1	Soap solution/Soap shavings	5 g
2	Distilled water (soft water)	100 mL
3	Hard water sample (or prepare using CaCl₂/MgCl₂)	100 mL
4	Calcium chloride (CaCl₂) or Magnesium chloride (MgCl₂)	1-2 g
5	Test tubes with corks/stoppers	4
6	Test tube stand	1
7	Measuring cylinder	2 (10 mL or 25 mL)
8	Beakers (100 mL or 250 mL)	2
9	Dropper	2
10	Glass rod	1
11	Spatula	1
12	Filter paper	As required
13	Funnel	1

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THEORY:

Water Hardness:
Water hardness is caused by the presence of dissolved salts of calcium (Ca²⁺) and magnesium (Mg²⁺) ions, particularly:

• Calcium chloride (CaCl₂)
• Magnesium chloride (MgCl₂)
• Calcium sulfate (CaSO₄)
• Magnesium sulfate (MgSO₄)
• Calcium bicarbonate [Ca(HCO₃)₂]
• Magnesium bicarbonate [Mg(HCO₃)₂]

Types of Water:

1. Soft Water:

• Water that does not contain dissolved salts of calcium and magnesium
• Easily forms lather with soap
• Examples: Distilled water, rainwater, water from rivers/lakes with low mineral content
• Good cleaning capacity with soap

2. Hard Water:

• Water that contains dissolved salts of calcium and magnesium
• Does not easily form lather with soap
• Examples: Groundwater, well water, seawater
• Poor cleaning capacity with soap
• Can be temporary (removed by boiling) or permanent hardness

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Soap:

• Sodium or potassium salts of long-chain fatty acids
• General formula: RCOONa (where R = long hydrocarbon chain)
• Examples: Sodium stearate (C₁₇H₃₅COONa), Sodium palmitate (C₁₅H₃₁COONa)

Action of Soap in Different Waters:

In Soft Water:

Soap molecule + Soft water → Lather formation (readily)
                            → Good cleaning action

• Soap dissolves easily
• Forms abundant stable lather/foam
• Effective cleaning occurs

In Hard Water:

2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl
(Soap)   + (Hard water) → (Calcium soap - scum/precipitate) + (Sodium chloride)

2RCOONa + MgCl₂ → (RCOO)₂Mg↓ + 2NaCl
(Soap)   + (Hard water) → (Magnesium soap - scum/precipitate) + (Sodium chloride)

• Soap reacts with Ca²⁺ and Mg²⁺ ions
• Forms insoluble calcium/magnesium soap (scum/curdy precipitate)
• Scum does not dissolve and forms white precipitate
• Lather forms only after all Ca²⁺ and Mg²⁺ ions are precipitated
• More soap is wasted
• Poor cleaning action

Cleaning Capacity: The ability of soap to form lather and remove dirt effectively. It is indicated by the amount of stable lather/foam formed.

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PROCEDURE:

PART A: PREPARATION OF SOLUTIONS

1. Preparation of Soap Solution:

1. Take about 5 g of soap shavings in a beaker.
2. Add about 100 mL of distilled water.
3. Warm gently with stirring using a glass rod until soap dissolves.
4. Allow it to cool.
5. Filter if necessary to get a clear soap solution.
6. Label it as “Soap Solution.”

2. Preparation of Hard Water:
If hard water sample is not available:

1. Take 100 mL of distilled water in a beaker.
2. Add about 1 g of calcium chloride (CaCl₂) or magnesium chloride (MgCl₂).
3. Stir well until it dissolves completely.
4. Label it as “Hard Water.”

3. Soft Water:

• Use distilled water directly
• Label it as “Soft Water”

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PART B: TESTING CLEANING CAPACITY

Test 1: With Soft Water (Distilled Water)

1. Take two clean test tubes and label them as S1 and S2.
2. Pour 10 mL of soft water (distilled water) in each test tube.
3. Add 2-3 drops of soap solution to test tube S1.
4. Cork the test tube and shake vigorously for about 30 seconds.
5. Observe the formation of lather/foam.
6. Measure the height of stable lather formed.
7. Observe if any scum/precipitate is formed at the bottom.
8. Repeat with test tube S2 for confirmation.
9. Record observations.

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Test 2: With Hard Water

1. Take two clean test tubes and label them as H1 and H2.
2. Pour 10 mL of hard water in each test tube.
3. Add 2-3 drops of soap solution to test tube H1.
4. Cork the test tube and shake vigorously for about 30 seconds.
5. Observe the formation of lather/foam.
6. Measure the height of lather formed (if any).
7. Observe if any scum/precipitate is formed.
8. If no lather forms, add more soap solution drop by drop (count the drops) and shake until stable lather appears.
9. Note the total number of soap drops required.
10. Repeat with test tube H2 for confirmation.
11. Record observations.

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OBSERVATIONS:

Observation Table:

Test Tube	Type of Water	Volume of Water	Drops of Soap Solution Added	Lather Formation	Height of Lather	Scum/Precipitate	Cleaning Capacity
S1	Soft water (Distilled)	10 mL	2-3 drops	Abundant, stable lather forms immediately	High (e.g., 2-3 cm)	No scum/precipitate observed	Excellent – Good cleaning capacity
S2	Soft water (Distilled)	10 mL	2-3 drops	Abundant, stable lather forms immediately	High (e.g., 2-3 cm)	No scum/precipitate observed	Excellent – Good cleaning capacity
H1	Hard water	10 mL	10-12 drops	Very little or no lather initially, forms after many drops	Low (e.g., 0.5 cm)	White curdy precipitate/scum observed	Poor – Low cleaning capacity
H2	Hard water	10 mL	10-12 drops	Very little or no lather initially, forms after many drops	Low (e.g., 0.5 cm)	White curdy precipitate/scum observed	Poor – Low cleaning capacity

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DETAILED OBSERVATIONS:

With Soft Water (Distilled Water):

• Only 2-3 drops of soap solution required
• Immediate and abundant lather formation
• Lather is stable and forms a thick foam layer
• Height of lather: High (approximately 2-3 cm)
• No scum or precipitate observed
• Solution remains clear below the lather
• Conclusion: Excellent cleaning capacity

With Hard Water:

• 10-12 drops or more of soap solution required
• No lather or very little lather forms initially
• White curdy precipitate/scum forms immediately
• Scum settles at the bottom
• Lather forms only after sufficient soap is added (after Ca²⁺/Mg²⁺ ions are precipitated)
• Height of lather: Very low (approximately 0.5 cm or less)
• Solution becomes cloudy/turbid
• Conclusion: Poor cleaning capacity

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CHEMICAL EQUATIONS:

Reaction of Soap with Hard Water (Calcium ions):

2C₁₇H₃₅COONa + CaCl₂ → (C₁₇H₃₅COO)₂Ca↓ + 2NaCl
(Sodium stearate - Soap) + (Calcium chloride) → (Calcium stearate - Scum) + (Sodium chloride)

Reaction of Soap with Hard Water (Magnesium ions):

2C₁₇H₃₅COONa + MgCl₂ → (C₁₇H₃₅COO)₂Mg↓ + 2NaCl
(Sodium stearate - Soap) + (Magnesium chloride) → (Magnesium stearate - Scum) + (Sodium chloride)

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RESULT:

Comparative Study of Cleaning Capacity:

Parameter	Soft Water	Hard Water
Lather Formation	Immediate and abundant	Delayed and scanty
Soap Required	Less (2-3 drops)	More (10-12 drops or more)
Scum Formation	No scum	White curdy scum formed
Height of Lather	High (2-3 cm)	Low (0.5 cm or less)
Cleaning Capacity	Excellent	Poor
Soap Wastage	Minimal	Significant

Conclusion:

1. Soap has excellent cleaning capacity in soft water (distilled water) as it forms abundant and stable lather easily with less soap.
2. Soap has poor cleaning capacity in hard water as it reacts with calcium and magnesium ions to form insoluble scum/precipitate, requiring more soap and producing less lather.
3. Soft water is better for cleaning purposes as it saves soap and provides effective cleaning action.
4. Hard water causes wastage of soap as soap is consumed in precipitating Ca²⁺ and Mg²⁺ ions before lather formation begins.

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PRECAUTIONS:

General:

1. Use clean and dry test tubes for accurate results.
2. Label all test tubes properly to avoid confusion.
3. Use equal volumes of water in all test tubes for fair comparison.
4. Add soap solution drop by drop and count accurately.

During Experiment:

5. Shake the test tubes vigorously and uniformly for the same duration (30 seconds).
6. Cork the test tubes tightly before shaking to prevent spillage.
7. Allow the test tubes to stand for a few seconds after shaking to observe stable lather.
8. Measure the lather height immediately after shaking as foam may collapse.
9. Observe carefully for scum formation at the bottom of the test tube.

For Soft Water Test:

10. Always use distilled water or deionized water as soft water.
11. Do not use tap water as it may contain dissolved minerals.

For Hard Water:

12. If preparing hard water, ensure calcium/magnesium salts are completely dissolved.
13. Use the same concentration of hard water for all tests.
14. If natural hard water is used, test its hardness first.

Safety:

15. Handle chemicals carefully and avoid direct contact with skin.
16. Wear safety goggles if available.
17. Do not taste or smell any chemical.
18. Clean all apparatus after use.
19. Dispose of solutions as per laboratory guidelines.
20. Wash hands thoroughly after the experiment.

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SOURCES OF ERROR:

1. Unequal shaking time or vigor may affect lather formation
2. Using tap water instead of distilled water (tap water may have some hardness)
3. Incorrect measurement of water volume
4. Not counting soap drops accurately
5. Observing lather height after foam has collapsed
6. Using different concentrations of hard water
7. Contaminated test tubes may affect results
8. Temperature variation may affect soap solubility

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VIVA QUESTIONS:

1. Q: What is hard water?

• A: Water that contains dissolved salts of calcium and magnesium, particularly chlorides, sulfates, and bicarbonates.

2. Q: What is soft water?

• A: Water that does not contain dissolved salts of calcium and magnesium and easily forms lather with soap.

3. Q: Why does soap not form lather easily in hard water?

• A: Because soap reacts with Ca²⁺ and Mg²⁺ ions present in hard water to form insoluble calcium/magnesium soap (scum), which does not produce lather.

4. Q: What is scum?

• A: Scum is the insoluble calcium or magnesium soap formed when soap reacts with hard water. It appears as a white curdy precipitate.

5. Q: Write the equation for the reaction between soap and hard water.

• A: 2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl

6. Q: Which type of water is better for washing clothes – soft or hard?

• A: Soft water is better because it forms lather easily, requires less soap, and has good cleaning capacity.

7. Q: Give two examples of soft water.

• A: Distilled water, rainwater

8. Q: Give two examples of hard water.

• A: Well water, groundwater, seawater

9. Q: What causes hardness in water?

• A: Presence of dissolved salts of calcium (Ca²⁺) and magnesium (Mg²⁺) ions.

10. Q: What are the two types of hardness in water?

• A:
  • Temporary hardness (can be removed by boiling)
  • Permanent hardness (cannot be removed by boiling)

11. Q: How can temporary hardness be removed?

• A: By boiling the water, which precipitates calcium and magnesium carbonates.

12. Q: What is the chemical name of soap?

• A: Sodium or potassium salts of long-chain fatty acids (e.g., sodium stearate, sodium palmitate)

13. Q: Why is more soap wasted in hard water?

• A: Because soap first reacts with Ca²⁺ and Mg²⁺ ions to form scum. Only after all these ions are precipitated does lather begin to form.

14. Q: What is the advantage of using detergents over soap in hard water?

• A: Detergents do not form insoluble precipitates with Ca²⁺ and Mg²⁺ ions, so they work well in both soft and hard water.

15. Q: What is lather?

• A: Lather is the foam or froth formed when soap is shaken with water. It indicates the cleaning capacity of soap.

16. Q: Name the salts commonly responsible for hardness in water.

• A: CaCl₂, MgCl₂, CaSO₄, MgSO₄, Ca(HCO₃)₂, Mg(HCO₃)₂

**17. Q: How can you prepare