Hard and Soft Water - Removal of Hardness - UNSOLVED PRACTICE SET
Chapter: Hydrogen | Topic: Hard and Soft Water Removal of Hardness
HARD AND SOFT WATER - REMOVAL OF HARDNESS - UNSOLVED PRACTICE SET
Topic: Hard and Soft Water Removal of Hardness
Multiple Choice Questions
Q1. Hard water contains high concentrations of:
- Sodium and potassium salts
- Calcium and magnesium salts
- Iron and copper salts
- Ammonium salts
Q2. Temporary hardness of water is caused by:
- CaCl₂ and MgCl₂
- CaSO₄ and MgSO₄
- Ca(HCO₃)₂ and Mg(HCO₃)₂
- CaCO₃ and MgCO₃
Q3. Permanent hardness can be removed by:
- Boiling
- Adding washing soda (Na₂CO₃)
- Both (a) and (b)
- Filtration only
Q4. The process of removing hardness by adding calculated amount of lime is called:
- Permutit process
- Calgon process
- Clark's process
- Ion exchange process
Q5. Synthetic ion exchange resins used for water softening are called:
- Zeolites
- Permutits
- Both (a) and (b)
- Neither (a) nor (b)
Q6. Soap does not lather well in hard water because:
- Soap is insoluble in water
- Soap forms insoluble precipitates with Ca²⁺ and Mg²⁺ ions
- Hard water destroys soap molecules
- Soap reacts with chlorine in hard water
Short Answer Questions
Q7. Differentiate between temporary hardness and permanent hardness of water. Name one salt responsible for each type.
Q8. Write chemical equations showing how boiling removes temporary hardness from water containing Ca(HCO₃)₂.
Q9. Explain Clark's method for removing temporary hardness using lime (Ca(OH)₂). Write the relevant chemical equation.
Q10. What is the Permutit (zeolite) process for softening hard water? Write the ion exchange reaction involved.
Q11. Your grandmother uses borax (Na₂B₄O₇·10H₂O) while washing clothes. How does borax help in softening water? Write the chemical reaction.
Q12. Why does hard water cause scaling in boilers and water heaters? What problems does this scaling create?
Long Answer Questions
Q13. Describe the various methods for removing temporary hardness of water:
(a) By boiling
(b) By Clark's method (addition of lime)
(c) By adding washing soda (Na₂CO₃)
Write balanced chemical equations for each method and mention their limitations.
Q14. Discuss the methods for removing permanent hardness of water:
(a) Washing soda method
(b) Permutit (zeolite) process
(c) Synthetic ion exchange resin method
(d) Calgon process
Explain the principle behind each method with chemical equations.
Q15. In many Indian households, especially in areas with hard water like Rajasthan and Gujarat, people struggle with white stains on utensils and reduced soap efficiency. Discuss:
(a) The health implications of drinking hard water
(b) Why hard water is actually beneficial in some ways
(c) The most practical method for a middle-class Indian family to soften water for domestic use
Numerical / Application-Based Problems
Q16. A sample of hard water contains 120 mg of CaSO₄ per litre.
(a) Calculate the hardness of water in terms of CaCO₃ equivalent (in ppm).
(b) Calculate the mass of washing soda (Na₂CO₃) required to soften 1000 litres of this water completely.
[Given: Molar masses: CaSO₄ = 136 g/mol, CaCO₃ = 100 g/mol, Na₂CO₃ = 106 g/mol]
Q17. In a titration experiment, 50 mL of hard water requires 15 mL of N/50 EDTA solution using Eriochrome Black T indicator. After boiling, the same 50 mL sample requires 10 mL of N/50 EDTA.
(a) Calculate the total hardness in ppm (as CaCO₃ equivalent).
(b) Calculate the temporary hardness in ppm.
(c) Calculate the permanent hardness in ppm.
[Hint: 1 mL of N/50 EDTA = 1 mg of CaCO₃ equivalent]
Q18. A water softener uses zeolite (Na₂Z) that can exchange sodium ions with calcium ions. The reaction is: Ca²⁺ + Na₂Z → CaZ + 2Na⁺
(a) If 1 kg of zeolite can remove 5000 mg of Ca²⁺ ions, how much zeolite is needed to soften 1000 L of water containing 200 ppm of Ca²⁺?
(b) After exhaustion, how can the zeolite be regenerated? Write the regeneration reaction.
(c) Why is this method preferred over chemical precipitation methods for domestic water softeners?