Carbon and Its Compounds
Soap and Hard Water | साबुन एवं कठोर जल
Class 10 Science | CBSE + Foundation + Competitive
Soap and Hard Water | साबुन एवं कठोर जल
1. Introduction | परिचय
Hard water is water that contains appreciable amounts of
dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions.
कठोर जल वह जल है जिसमें कैल्शियम (Ca²⁺) और मैग्नीशियम (Mg²⁺) के आयन पर्याप्त मात्रा में घुले होते हैं।
Soap does not work efficiently in hard water because it reacts with Ca²⁺ and Mg²⁺ ions and forms insoluble substances called scum.
कठोर जल वह जल है जिसमें कैल्शियम (Ca²⁺) और मैग्नीशियम (Mg²⁺) के आयन पर्याप्त मात्रा में घुले होते हैं।
Soap does not work efficiently in hard water because it reacts with Ca²⁺ and Mg²⁺ ions and forms insoluble substances called scum.
2. What is Soap? | साबुन क्या है?
Soap is generally the sodium or potassium salt of a
long-chain fatty acid.
Example:
Example:
Sodium stearate = C₁₇H₃₅COONa
Its structural representation is:
CH₃–(CH₂)₁₆–COO⁻ Na⁺
The long hydrocarbon chain is hydrophobic and the ionic
carboxylate end is hydrophilic.
3. What is Hard Water? | कठोर जल क्या है?
Water containing dissolved salts of calcium and magnesium is
called hard water.
The important ions responsible for hardness are:
Ca²⁺ → Calcium ion
Mg²⁺ → Magnesium ion
The important ions responsible for hardness are:
Ca²⁺ → Calcium ion
Mg²⁺ → Magnesium ion
Remember:
Hard Water → Ca²⁺ + Mg²⁺
इन आयनों के कारण साबुन के साथ अवक्षेप बनने लगता है।
Hard Water → Ca²⁺ + Mg²⁺
इन आयनों के कारण साबुन के साथ अवक्षेप बनने लगता है।
4. Types of Hardness of Water | जल की कठोरता के प्रकार
| Type | Main Cause | Removal |
|---|---|---|
| Temporary Hardness | Bicarbonates of Ca and Mg | Boiling can remove it |
| Permanent Hardness | Chlorides and sulphates of Ca and Mg | Cannot be removed simply by boiling |
Temporary hardness:
Ca(HCO₃)₂ and Mg(HCO₃)₂ are important causes.
Permanent hardness:
CaCl₂, MgCl₂, CaSO₄ and MgSO₄ are common causes.
Ca(HCO₃)₂ and Mg(HCO₃)₂ are important causes.
Permanent hardness:
CaCl₂, MgCl₂, CaSO₄ and MgSO₄ are common causes.
5. Why Does Soap Not Work Well in Hard Water?
साबुन कठोर जल में अच्छी तरह कार्य क्यों नहीं करता?
साबुन कठोर जल में अच्छी तरह कार्य क्यों नहीं करता?
When soap is added to hard water, its carboxylate ions
react with Ca²⁺ and Mg²⁺ ions.
This produces insoluble calcium and magnesium salts of
fatty acids.
These insoluble salts appear as a sticky material called
scum.
6. Reaction of Soap with Calcium Ions
| कैल्शियम आयन के साथ साबुन की अभिक्रिया
2RCOONa + CaCl₂ → (RCOO)₂Ca ↓ + 2NaCl
Here:
RCOONa = Sodium soap
CaCl₂ = Calcium salt present in hard water
(RCOO)₂Ca = Insoluble calcium soap
↓ = Precipitate
RCOONa = Sodium soap
CaCl₂ = Calcium salt present in hard water
(RCOO)₂Ca = Insoluble calcium soap
↓ = Precipitate
7. Reaction of Soap with Magnesium Ions
| मैग्नीशियम आयन के साथ साबुन की अभिक्रिया
2RCOONa + MgCl₂ → (RCOO)₂Mg ↓ + 2NaCl
The magnesium salt formed is also insoluble and contributes
to scum formation.
8. What is Scum? | स्कम क्या है?
Scum is the insoluble calcium or magnesium salt of
a fatty acid formed when soap reacts with hard water.
स्कम कठोर जल में साबुन की Ca²⁺ और Mg²⁺ आयनों के साथ अभिक्रिया से बनने वाला अघुलनशील पदार्थ है।
स्कम कठोर जल में साबुन की Ca²⁺ और Mg²⁺ आयनों के साथ अभिक्रिया से बनने वाला अघुलनशील पदार्थ है।
Soap + Ca²⁺ / Mg²⁺ → Insoluble Scum ↓
9. Why is Soap Wasted in Hard Water?
| कठोर जल में साबुन क्यों नष्ट होता है?
A part of the soap reacts with Ca²⁺ and Mg²⁺ ions instead
of cleaning the dirt.
Therefore, more soap is required to produce sufficient
cleansing action.
अर्थात साबुन का कुछ भाग सफाई करने के बजाय कठोर जल के Ca²⁺ और Mg²⁺ आयनों के साथ अभिक्रिया करके स्कम बना देता है।
अर्थात साबुन का कुछ भाग सफाई करने के बजाय कठोर जल के Ca²⁺ और Mg²⁺ आयनों के साथ अभिक्रिया करके स्कम बना देता है।
10. Effect of Scum on Clothes | कपड़ों पर स्कम का प्रभाव
Scum can stick to fabrics and may make them appear dull.
It can also reduce the efficiency of washing.
स्कम कपड़ों के रेशों पर चिपक सकता है और कपड़ों को फीका या मैला दिखा सकता है।
स्कम कपड़ों के रेशों पर चिपक सकता है और कपड़ों को फीका या मैला दिखा सकता है।
11. Effect on Cleansing Action | सफाई क्रिया पर प्रभाव
In soft water:
Soap remains available for cleansing and can form micelles effectively.
In hard water:
A considerable amount of soap is consumed in forming insoluble calcium/magnesium salts. Therefore, cleansing efficiency decreases.
Soap remains available for cleansing and can form micelles effectively.
In hard water:
A considerable amount of soap is consumed in forming insoluble calcium/magnesium salts. Therefore, cleansing efficiency decreases.
12. Soap and Micelle Formation in Soft Water
| मुलायम जल में साबुन और मिसेल
In soft water, soap molecules can arrange around grease
particles and form micelles.
The hydrophobic tails point towards grease while hydrophilic
heads point towards water.
Soft Water
Soap + Water + Grease
↓
Hydrophobic tails → Grease
Hydrophilic heads → Water
↓
Micelle Formation
↓
Grease removed during washing
Soap + Water + Grease
↓
Hydrophobic tails → Grease
Hydrophilic heads → Water
↓
Micelle Formation
↓
Grease removed during washing
13. Soap and Hard Water | साबुन एवं कठोर जल
Hard Water
Soap + Ca²⁺ / Mg²⁺
↓
Insoluble Calcium/Magnesium Soap
↓
Scum Formation
↓
Soap Wastage
↓
Reduced Cleansing Efficiency
Soap + Ca²⁺ / Mg²⁺
↓
Insoluble Calcium/Magnesium Soap
↓
Scum Formation
↓
Soap Wastage
↓
Reduced Cleansing Efficiency
14. Soft Water vs Hard Water
| मुलायम जल बनाम कठोर जल
| Property | Soft Water | Hard Water |
|---|---|---|
| Ca²⁺/Mg²⁺ | Very low/insignificant | Appreciable amount |
| Soap action | Effective | Less effective |
| Scum | Little/no scum due to hardness | Forms scum |
| Soap requirement | Less | More |
| Micelle formation | Relatively effective | Soap is consumed by Ca/Mg ions |
15. Temporary Hardness | अस्थायी कठोरता
Temporary hardness is mainly caused by bicarbonates of
calcium and magnesium.
For example:
Ca(HCO₃)₂
Mg(HCO₃)₂
It can generally be reduced by boiling.
Ca(HCO₃)₂
Mg(HCO₃)₂
It can generally be reduced by boiling.
Ca(HCO₃)₂ → CaCO₃ ↓ + CO₂ + H₂O
16. Permanent Hardness | स्थायी कठोरता
Permanent hardness is mainly due to dissolved chlorides and
sulphates of calcium and magnesium.
Examples:
CaCl₂, MgCl₂, CaSO₄ and MgSO₄
Simple boiling does not remove permanent hardness.
CaCl₂, MgCl₂, CaSO₄ and MgSO₄
Simple boiling does not remove permanent hardness.
17. How Can Hardness Be Reduced?
| कठोरता को कैसे कम किया जा सकता है?
Depending on the type of hardness, methods include:
1. Boiling → Mainly useful for temporary hardness.
2. Washing soda → Can precipitate calcium ions.
3. Ion-exchange methods → Used for water softening.
4. Modern water-softening processes → Used in domestic and industrial applications.
1. Boiling → Mainly useful for temporary hardness.
2. Washing soda → Can precipitate calcium ions.
3. Ion-exchange methods → Used for water softening.
4. Modern water-softening processes → Used in domestic and industrial applications.
18. Why Detergents Work Better in Hard Water?
डिटर्जेंट कठोर जल में बेहतर क्यों काम करते हैं?
डिटर्जेंट कठोर जल में बेहतर क्यों काम करते हैं?
Synthetic detergents generally do not form insoluble calcium
and magnesium salts in the same way ordinary soaps do.
Therefore, they generally remain effective in hard water.
Exam Point:
Soap + Hard Water → Scum
Detergent + Hard Water → Generally no insoluble scum of the same type
Soap + Hard Water → Scum
Detergent + Hard Water → Generally no insoluble scum of the same type
19. Chemical Reason Behind Soap Failure
| साबुन की विफलता का रासायनिक कारण
Soap contains the carboxylate ion:
RCOO⁻
Ca²⁺ and Mg²⁺ ions have strong interactions with carboxylate
ions and form insoluble salts:
2RCOO⁻ + Ca²⁺ → (RCOO)₂Ca ↓
2RCOO⁻ + Mg²⁺ → (RCOO)₂Mg ↓
20. Important Comparison | महत्वपूर्ण तुलना
| Soap | Hard Water Effect |
|---|---|
| RCOONa | Reacts with Ca²⁺/Mg²⁺ |
| Hydrophilic head | Forms insoluble Ca/Mg salts |
| Hydrophobic tail | Its cleansing role is reduced because soap is consumed |
| Overall | Scum formation and reduced efficiency |
21. 30 MCQs | बहुविकल्पीय प्रश्न
Q1. Hard water mainly contains:
A) Ca²⁺ and Mg²⁺ ions
B) Na⁺ and K⁺ ions only
C) H⁺ ions only
D) Cl₂ molecules
Answer: A
Q2. Soap is generally a salt of:
A) Mineral acid
B) Long-chain fatty acid
C) Alcohol
D) Alkene
Answer: B
Q3. The insoluble substance formed when soap reacts with hard water is:
A) Micelle
B) Ester
C) Scum
D) Alcohol
Answer: C
Q4. Which ions are mainly responsible for the formation of scum?
A) Na⁺
B) K⁺
C) H⁺
D) Ca²⁺ and Mg²⁺
Answer: D
Q5. Sodium stearate has the formula:
A) C₁₇H₃₅COONa
B) CH₃COOH
C) C₂H₅OH
D) CH₃CHO
Answer: A
Q6. Which ion reacts with soap to form calcium soap?
A) Na⁺
B) Ca²⁺
C) H⁺
D) Cl⁻
Answer: B
Q7. The calcium salt formed from soap is generally:
A) Highly soluble
B) Gaseous
C) Insoluble
D) Metallic
Answer: C
Q8. Which type of hardness can generally be reduced by boiling?
A) Permanent hardness
B) Temporary hardness
C) Both always
D) No hardness
Answer: B
Q9. Temporary hardness is mainly caused by:
A) Bicarbonates of Ca and Mg
B) NaCl
C) KCl
D) HCl
Answer: A
Q10. Permanent hardness is commonly caused by:
A) NaHCO₃
B) KOH
C) CaCl₂ and MgSO₄
D) H₂O
Answer: C
Q11. In hard water, soap is:
A) More effective
B) Less effective
C) Converted into oxygen
D) Converted into hydrogen
Answer: B
Q12. The reaction of soap with CaCl₂ produces:
A) Calcium soap
B) Ethanol
C) Ethene
D) Methane
Answer: A
Q13. The symbol ↓ in a chemical equation usually indicates:
A) Gas
B) Heat
C) Precipitate
D) Light
Answer: C
Q14. Which substance is generally more effective in hard water?
A) Soap
B) Detergent
C) Fat
D) Wax
Answer: B
Q15. Scum mainly consists of:
A) Soluble sodium salts
B) Insoluble calcium and magnesium salts of fatty acids
C) Water molecules
D) Alcohols
Answer: B
Q16. Which ion does NOT normally cause hardness of water?
A) Ca²⁺
B) Mg²⁺
C) Na⁺
D) Both A and B
Answer: C
Q17. Soap is wasted in hard water because it:
A) Evaporates
B) Burns
C) Reacts with Ca²⁺ and Mg²⁺
D) Becomes oxygen
Answer: C
Q18. Which of the following represents soap?
A) RCOONa
B) R–OH
C) R–CHO
D) R–Cl
Answer: A
Q19. Which salt can cause permanent hardness?
A) CaCl₂
B) NaCl
C) KCl
D) Na₂CO₃
Answer: A
Q20. Soap reacts with Mg²⁺ to form:
A) Soluble magnesium salt
B) Insoluble magnesium soap
C) Ethanol
D) Oxygen
Answer: B
Q21. Temporary hardness can be reduced by:
A) Boiling
B) Freezing
C) Filtration only
D) Evaporation only
Answer: A
Q22. Which compound is associated with temporary hardness?
A) Ca(HCO₃)₂
B) NaCl
C) KNO₃
D) NaOH
Answer: A
Q23. Which of the following is generally NOT removed by simple boiling?
A) Temporary hardness
B) Permanent hardness
C) Bicarbonate hardness
D) Some temporary hardness
Answer: B
Q24. Detergents are generally preferred over soaps in:
A) Hard water
B) Pure dry air
C) Metals
D) Sand
Answer: A
Q25. Which reaction represents soap-scum formation?
A) RCOONa + NaCl
B) 2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl
C) RCOONa + H₂O
D) RCOONa + O₂
Answer: B
Q26. Hard water increases soap consumption because:
A) Soap reacts with Ca²⁺/Mg²⁺
B) Soap evaporates
C) Soap becomes gas
D) Soap freezes
Answer: A
Q27. Which part of soap reacts to form insoluble salts with Ca²⁺?
A) Hydrocarbon tail
B) Carboxylate group
C) Methyl group only
D) Oxygen gas
Answer: B
Q28. Which ions are removed from temporary hard water on boiling by formation of carbonates?
A) Ca²⁺/Mg²⁺
B) Na⁺ only
C) K⁺ only
D) Cl⁻ only
Answer: A
Q29. A major disadvantage of soap in hard water is:
A) Formation of scum
B) Formation of oxygen
C) Formation of hydrogen
D) Formation of carbon dioxide
Answer: A
Q30. The best explanation for reduced cleansing efficiency of soap in hard water is:
A) Soap reacts with Ca²⁺/Mg²⁺ and becomes insoluble
B) Water becomes acidic
C) Soap changes into sugar
D) Soap evaporates immediately
Answer: A
22. 30 Subjective Questions | वर्णनात्मक प्रश्न
1 Mark
Q1. What is hard water?
Q1. What is hard water?
Answer: Water containing appreciable amounts of Ca²⁺ and Mg²⁺ ions is called hard water.
1 Mark
Q2. Name two ions responsible for hardness of water.
Q2. Name two ions responsible for hardness of water.
Answer: Ca²⁺ and Mg²⁺.
1 Mark
Q3. What is scum?
Q3. What is scum?
Answer: Scum is the insoluble calcium or magnesium salt of fatty acids formed when soap reacts with hard water.
1 Mark
Q4. Name the two types of hardness of water.
Q4. Name the two types of hardness of water.
Answer: Temporary hardness and permanent hardness.
1 Mark
Q5. Which type of hardness can generally be removed by boiling?
Q5. Which type of hardness can generally be removed by boiling?
Answer: Temporary hardness.
2 Marks
Q6. Why does soap not work well in hard water?
Q6. Why does soap not work well in hard water?
Soap reacts with Ca²⁺ and Mg²⁺ ions and forms insoluble salts called scum. Hence soap becomes less effective.
2 Marks
Q7. What is the difference between soft water and hard water?
Q7. What is the difference between soft water and hard water?
Soft water contains very little Ca²⁺/Mg²⁺, while hard water contains appreciable Ca²⁺/Mg²⁺ ions.
2 Marks
Q8. What happens when sodium soap is treated with calcium chloride?
Q8. What happens when sodium soap is treated with calcium chloride?
An insoluble calcium soap is formed:
2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl
2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl
2 Marks
Q9. What is temporary hardness?
Q9. What is temporary hardness?
Temporary hardness is hardness mainly caused by bicarbonates of calcium and magnesium and can generally be reduced by boiling.
2 Marks
Q10. What is permanent hardness?
Q10. What is permanent hardness?
Permanent hardness is mainly caused by chlorides and sulphates of calcium and magnesium and is not removed simply by boiling.
3 Marks
Q11. Explain the formation of scum.
Q11. Explain the formation of scum.
Ca²⁺ and Mg²⁺ ions present in hard water react with soap molecules. Insoluble calcium and magnesium salts of fatty acids are formed. These insoluble salts are called scum.
3 Marks
Q12. Write the chemical equation for the reaction of soap with CaCl₂.
Q12. Write the chemical equation for the reaction of soap with CaCl₂.
2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl
The insoluble calcium soap forms scum.
The insoluble calcium soap forms scum.
3 Marks
Q13. Explain why soap is wasted in hard water.
Q13. Explain why soap is wasted in hard water.
Some soap reacts with Ca²⁺ and Mg²⁺ ions to form insoluble salts. Therefore, that portion of soap is unavailable for cleansing and additional soap is needed.
3 Marks
Q14. Differentiate between temporary and permanent hardness.
Q14. Differentiate between temporary and permanent hardness.
Temporary: Mainly due to bicarbonates; can generally be reduced by boiling.
Permanent: Mainly due to chlorides and sulphates; not removed simply by boiling.
Permanent: Mainly due to chlorides and sulphates; not removed simply by boiling.
3 Marks
Q15. Why are detergents generally more suitable than soaps for hard water?
Q15. Why are detergents generally more suitable than soaps for hard water?
Detergents generally do not form insoluble calcium and magnesium salts in the same way ordinary soaps do. Hence they remain effective in hard water.
4 Marks
Q16. Explain the effect of hard water on cleansing action of soap.
Q16. Explain the effect of hard water on cleansing action of soap.
Hard water contains Ca²⁺ and Mg²⁺ ions. These ions react with soap and form insoluble calcium and magnesium salts called scum. Soap is therefore consumed in this reaction and less soap remains for cleansing. Hence cleansing efficiency decreases.
4 Marks
Q17. Write the reactions of soap with calcium and magnesium salts.
Q17. Write the reactions of soap with calcium and magnesium salts.
With calcium:
2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl
With magnesium:
2RCOONa + MgCl₂ → (RCOO)₂Mg↓ + 2NaCl
2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl
With magnesium:
2RCOONa + MgCl₂ → (RCOO)₂Mg↓ + 2NaCl
4 Marks
Q18. Explain temporary hardness of water.
Q18. Explain temporary hardness of water.
Temporary hardness is mainly caused by Ca(HCO₃)₂ and Mg(HCO₃)₂. On boiling, bicarbonates decompose and insoluble carbonates may precipitate. Thus the hardness can generally be reduced by boiling.
4 Marks
Q19. Explain permanent hardness of water.
Q19. Explain permanent hardness of water.
Permanent hardness is mainly caused by soluble chlorides and sulphates of calcium and magnesium. Examples include CaCl₂, MgCl₂, CaSO₄ and MgSO₄. Simple boiling does not remove this hardness.
4 Marks
Q20. Why is more soap required in hard water?
Q20. Why is more soap required in hard water?
Because part of the soap reacts with Ca²⁺ and Mg²⁺ ions and forms insoluble scum. The soap consumed in this reaction is not available for cleansing, so more soap is needed.
5 Marks
Q21. Explain why soap is ineffective in hard water with an equation.
Q21. Explain why soap is ineffective in hard water with an equation.
Hard water contains Ca²⁺ and Mg²⁺ ions. These ions react with soap:
2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl
The insoluble calcium soap forms scum. Similar reaction occurs with Mg²⁺. As a result, soap is wasted and cleansing efficiency decreases.
2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl
The insoluble calcium soap forms scum. Similar reaction occurs with Mg²⁺. As a result, soap is wasted and cleansing efficiency decreases.
5 Marks
Q22. Describe the difference between soap action in soft water and hard water.
Q22. Describe the difference between soap action in soft water and hard water.
Soft water: Soap remains available for cleansing and forms micelles around grease effectively.
Hard water: Ca²⁺ and Mg²⁺ react with soap to form insoluble scum. Thus less soap is available for micelle formation and cleansing becomes less efficient.
Hard water: Ca²⁺ and Mg²⁺ react with soap to form insoluble scum. Thus less soap is available for micelle formation and cleansing becomes less efficient.
5 Marks
Q23. Explain scum formation and its disadvantages.
Q23. Explain scum formation and its disadvantages.
Scum forms when soap reacts with Ca²⁺ and Mg²⁺ ions. The insoluble calcium/magnesium salts of fatty acids are deposited.
Disadvantages:
1. Soap is wasted.
2. Cleansing efficiency decreases.
3. Scum may stick to fabrics.
4. More soap is required.
Disadvantages:
1. Soap is wasted.
2. Cleansing efficiency decreases.
3. Scum may stick to fabrics.
4. More soap is required.
5 Marks
Q24. Explain temporary and permanent hardness with examples.
Q24. Explain temporary and permanent hardness with examples.
Temporary hardness is caused mainly by bicarbonates such as Ca(HCO₃)₂ and Mg(HCO₃)₂ and can generally be reduced by boiling.
Permanent hardness is caused mainly by chlorides and sulphates such as CaCl₂, MgCl₂, CaSO₄ and MgSO₄ and cannot be removed simply by boiling.
Permanent hardness is caused mainly by chlorides and sulphates such as CaCl₂, MgCl₂, CaSO₄ and MgSO₄ and cannot be removed simply by boiling.
5 Marks
Q25. Why are detergents better than soaps in hard water?
Q25. Why are detergents better than soaps in hard water?
Soaps form insoluble calcium and magnesium salts in hard water. These salts form scum and reduce cleansing efficiency. Detergents generally avoid this problem and therefore remain effective in hard water.
6 Marks
Q26. Explain in detail why soap does not work efficiently in hard water.
Q26. Explain in detail why soap does not work efficiently in hard water.
Hard water contains Ca²⁺ and Mg²⁺ ions. Soap contains carboxylate ions. When soap is added to hard water, these ions react to form insoluble calcium and magnesium salts.
For example:
2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl
The insoluble product is called scum. Soap is therefore consumed in scum formation rather than cleansing. This reduces micelle formation and increases soap consumption.
For example:
2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl
The insoluble product is called scum. Soap is therefore consumed in scum formation rather than cleansing. This reduces micelle formation and increases soap consumption.
6 Marks
Q27. Explain the chemical reactions involved in scum formation.
Q27. Explain the chemical reactions involved in scum formation.
Soap may be represented as RCOONa.
With calcium ions:
2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl
With magnesium ions:
2RCOONa + MgCl₂ → (RCOO)₂Mg↓ + 2NaCl
The insoluble products form scum and reduce the effectiveness of soap.
With calcium ions:
2RCOONa + CaCl₂ → (RCOO)₂Ca↓ + 2NaCl
With magnesium ions:
2RCOONa + MgCl₂ → (RCOO)₂Mg↓ + 2NaCl
The insoluble products form scum and reduce the effectiveness of soap.
6 Marks
Q28. Compare temporary and permanent hardness of water.
Q28. Compare temporary and permanent hardness of water.
| Basis | Temporary Hardness | Permanent Hardness |
|---|---|---|
| Main cause | Ca/Mg bicarbonates | Ca/Mg chlorides and sulphates |
| Example | Ca(HCO₃)₂ | CaCl₂ |
| Boiling | Generally removes/reduces it | Does not remove it simply |
6 Marks
Q29. Explain the difference between soap and detergent in hard water.
Q29. Explain the difference between soap and detergent in hard water.
Soap reacts with Ca²⁺ and Mg²⁺ ions and produces insoluble scum. Therefore its cleansing efficiency decreases in hard water.
Detergents generally do not form insoluble calcium and magnesium salts in the same manner. Hence they generally work better in hard water.
Detergents generally do not form insoluble calcium and magnesium salts in the same manner. Hence they generally work better in hard water.
6 Marks
Q30. Write a detailed note on soap and hard water.
Q30. Write a detailed note on soap and hard water.
Hard water contains Ca²⁺ and Mg²⁺ ions. Soap is the sodium or potassium salt of a long-chain fatty acid.
When soap is added to hard water, Ca²⁺ and Mg²⁺ ions react with the carboxylate part of soap and form insoluble calcium and magnesium soaps.
These insoluble substances are called scum. Scum wastes soap, may deposit on fabrics and reduces cleansing efficiency.
Temporary hardness is mainly due to bicarbonates and can generally be reduced by boiling, whereas permanent hardness is mainly due to chlorides and sulphates and is not removed simply by boiling.
Detergents generally remain more effective than soaps in hard water.
When soap is added to hard water, Ca²⁺ and Mg²⁺ ions react with the carboxylate part of soap and form insoluble calcium and magnesium soaps.
These insoluble substances are called scum. Scum wastes soap, may deposit on fabrics and reduces cleansing efficiency.
Temporary hardness is mainly due to bicarbonates and can generally be reduced by boiling, whereas permanent hardness is mainly due to chlorides and sulphates and is not removed simply by boiling.
Detergents generally remain more effective than soaps in hard water.
23. Quick Revision | त्वरित पुनरावृत्ति
| Point | Remember |
|---|---|
| Hard Water | Contains Ca²⁺ and Mg²⁺ ions |
| Soap | Na/K salt of long-chain fatty acid |
| Scum | Insoluble Ca/Mg salts of fatty acids |
| Temporary Hardness | Mainly bicarbonates |
| Permanent Hardness | Mainly chlorides and sulphates |
| Boiling | Generally reduces temporary hardness |
| Soap in Hard Water | Less effective |
| Detergent | Generally effective in hard water |
🔥 Board Exam Golden Points:
1. Hard water contains Ca²⁺ and Mg²⁺ ions.
2. Soap is generally a sodium/potassium salt of long-chain fatty acids.
3. Soap reacts with Ca²⁺ and Mg²⁺ to form insoluble salts.
4. Insoluble salts are called scum.
5. Scum causes soap wastage.
6. Soap becomes less effective in hard water.
7. Temporary hardness is mainly due to bicarbonates.
8. Permanent hardness is mainly due to chlorides and sulphates.
9. Temporary hardness can generally be reduced by boiling.
10. Detergents are generally more effective in hard water.
1. Hard water contains Ca²⁺ and Mg²⁺ ions.
2. Soap is generally a sodium/potassium salt of long-chain fatty acids.
3. Soap reacts with Ca²⁺ and Mg²⁺ to form insoluble salts.
4. Insoluble salts are called scum.
5. Scum causes soap wastage.
6. Soap becomes less effective in hard water.
7. Temporary hardness is mainly due to bicarbonates.
8. Permanent hardness is mainly due to chlorides and sulphates.
9. Temporary hardness can generally be reduced by boiling.
10. Detergents are generally more effective in hard water.
Carbon and Its Compounds | Soap and Hard Water
साबुन एवं कठोर जल
CBSE Class 10 | Foundation | Competitive Preparation
साबुन एवं कठोर जल
CBSE Class 10 | Foundation | Competitive Preparation
