Water - Structure, Properties & Reactions - UNSOLVED PRACTICE SET
Chapter: Hydrogen | Topic: Water Structure Properties Reactions
WATER - STRUCTURE, PROPERTIES & REACTIONS - UNSOLVED PRACTICE SET
Topic: Water Structure Properties Reactions
Multiple Choice Questions
Q1. The bond angle in a water molecule is approximately:
- 90°
- 104.5°
- 109.5°
- 120°
Q2. Water has a high boiling point compared to H₂S because of:
- Covalent bonding
- Hydrogen bonding
- Ionic bonding
- Metallic bonding
Q3. The hybridisation of oxygen in water is:
- sp
- sp²
- sp³
- dsp³
Q4. Water shows maximum density at:
- 0°C
- 4°C
- 100°C
- -4°C
Q5. When water reacts with calcium metal, the products are:
- Calcium hydroxide and hydrogen gas
- Calcium oxide and hydrogen gas
- Calcium hydride and oxygen gas
- No reaction occurs
Q6. The autoionisation of water is represented by:
- H₂O → H⁺ + OH⁻
- 2H₂O ⇌ H₃O⁺ + OH⁻
- H₂O → 2H + O
- H₂O + H₂ → 2H₂O
Short Answer Questions
Q7. Draw the Lewis structure of water and explain why the bond angle is 104.5° instead of the ideal tetrahedral angle of 109.5°.
Q8. Explain why ice floats on water. How does this property affect aquatic life in Indian lakes during winter?
Q9. Water acts as an amphoteric substance. Explain what this means with one example each of water acting as an acid and as a base.
Q10. Write balanced chemical equations for the reaction of water with:
(a) Sodium metal
(b) Calcium carbide
(c) Carbon dioxide
Q11. Your mother boils water before drinking during the monsoon season in Mumbai. What chemical and biological impurities does boiling remove or reduce?
Q12. Why does water have a high specific heat capacity (4.18 J/g°C)? How does this property help regulate Earth's temperature?
Long Answer Questions
Q13. Describe the structure of water molecule using VSEPR theory and hybridisation. Explain:
(a) The bent shape of the molecule
(b) The presence of two lone pairs on oxygen
(c) The polar nature of the O–H bond
(d) How these features lead to hydrogen bonding
Q14. Discuss the anomalous properties of water due to hydrogen bonding:
(a) High boiling point and melting point
(b) Expansion upon freezing (maximum density at 4°C)
(c) High specific heat and heat of vaporisation
(d) Excellent solvent properties
Give real-life examples where each property is important.
Q15. Water is called the "universal solvent" and is essential for life. However, many parts of India face water scarcity. Discuss:
(a) The chemical properties that make water an excellent solvent
(b) Why water is essential for biochemical reactions in our body
(c) One chemical method and one physical method to purify water for drinking
Numerical / Application-Based Problems
Q16. The density of water at 4°C is 1.000 g/mL, while the density of ice at 0°C is 0.917 g/mL.
(a) Calculate the volume occupied by 100 g of water at 4°C.
(b) Calculate the volume occupied by the same 100 g when it freezes into ice at 0°C.
(c) Calculate the percentage increase in volume upon freezing. Explain why this expansion can crack water pipes in cold places like Shimla.
Q17. The autoionisation constant of water (Kw) at 25°C is 1.0 × 10⁻¹⁴.
(a) Calculate the concentration of H⁺ ions in pure water at 25°C.
(b) If the concentration of H⁺ ions in a sample of rainwater is 1.0 × 10⁻⁵ M, calculate the concentration of OH⁻ ions.
(c) Is this rainwater acidic, basic, or neutral? Explain.
Q18. A family in Delhi uses 100 litres of water per day for drinking and cooking. They want to install a water purifier that uses reverse osmosis.
(a) If the purifier removes 95% of dissolved salts, and the input water has 500 ppm of dissolved solids, calculate the ppm of dissolved solids in the purified water.
(b) If 3 litres of water are wasted for every 1 litre purified, how much total water is consumed to produce 100 litres of purified water?
(c) Suggest one way to reduce water wastage in such systems.