Heavy Water - UNSOLVED PRACTICE SET
Chapter: Hydrogen | Topic: Heavy Water
HEAVY WATER - UNSOLVED PRACTICE SET
Topic: Heavy Water
Multiple Choice Questions
Q1. Heavy water is represented by the formula:
- H₂O
- D₂O
- T₂O
- HDO
Q2. Heavy water was discovered by:
- Henry Cavendish
- Harold Urey
- Ernest Rutherford
- Niels Bohr
Q3. The density of heavy water at 20°C is approximately:
- 0.90 g/mL
- 1.00 g/mL
- 1.11 g/mL
- 1.50 g/mL
Q4. Heavy water is used as a moderator in nuclear reactors because it:
- Is radioactive
- Slows down fast neutrons effectively
- Absorbs neutrons completely
- Is cheaper than normal water
Q5. The boiling point of heavy water is:
- Lower than normal water
- The same as normal water
- Higher than normal water
- It doesn't boil
Q6. Which of the following statements about heavy water is FALSE?
- It is toxic to humans if consumed in large quantities
- It supports aquatic life normally
- It is used as a tracer in chemical reactions
- It has a higher freezing point than normal water
Short Answer Questions
Q7. How is heavy water prepared from normal water? Mention one physical method and one chemical method briefly.
Q8. Compare the physical properties of heavy water (D₂O) and normal water (H₂O) — mention at least three differences.
Q9. Why is heavy water called a "moderator" in nuclear reactors? What would happen if normal water were used instead in some reactors?
Q10. Write the reaction of heavy water with sodium metal. How does it differ from the reaction of normal water with sodium?
Q11. Your teacher mentions that heavy water can be used to study reaction mechanisms. Explain how D₂O acts as a tracer in chemical research.
Q12. Why is heavy water more expensive to produce than normal water? What makes its separation difficult?
Long Answer Questions
Q13. Describe the preparation of heavy water by:
(a) Fractional distillation
(b) Electrolysis of water
(c) Chemical exchange methods (like H₂S–H₂O exchange)
Explain the principle behind each method and why these methods work based on the slight differences between H₂O and D₂O.
Q14. Discuss the chemical properties of heavy water by comparing its reactions with those of normal water:
(a) Reaction with metals
(b) Reaction with metal oxides
(c) Reaction with carbides
(d) Reaction with salts (hydrolysis)
Write balanced equations for each and highlight any differences in reaction rates or products.
Q15. Heavy water plays a crucial role in India's nuclear power program. The country has heavy water plants in places like Kota (Rajasthan) and Tuticorin (Tamil Nadu). Discuss:
(a) Why heavy water is essential for PHWRs (Pressurised Heavy Water Reactors) used in India
(b) The advantage of using heavy water over normal water as a moderator
(c) One environmental and one economic concern related to heavy water production
Numerical / Application-Based Problems
Q16. The molar mass of heavy water (D₂O) is 20 g/mol, while that of normal water (H₂O) is 18 g/mol.
(a) Calculate the percentage increase in molar mass from H₂O to D₂O.
(b) If you have 500 g of D₂O, calculate how many moles it contains.
(c) Calculate the mass of 2.5 moles of D₂O.
Q17. A sample containing a mixture of H₂O and D₂O has an average molar mass of 19 g/mol.
(a) Let the mole fraction of D₂O be x. Set up an equation to find x.
(b) Solve for x to find the mole fraction of D₂O in the mixture.
(c) Calculate the mass percentage of D₂O in the mixture.
Q18. In a nuclear reactor, 1000 kg of heavy water is used as a moderator. Due to leakage, 2% of the heavy water is lost every month and needs to be replaced.
(a) Calculate the mass of heavy water lost in the first month.
(b) If heavy water costs ₹ 30,000 per kg, calculate the monthly cost of replacement.
(c) Why is it important to prevent even small leaks of heavy water in a nuclear reactor?