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Vidaara.orgClass 11 · Chemistry
CodeVID-C11-09-T2-01
Assignment — Hydrides & Water
Chapter: Hydrogen
Topic: Hydrides & Water
Maximum Marks: 30
Time: 60 minutes
Name: ____________________ Roll No.: __________ Date: ____________

General Instructions

  • All questions are compulsory.
  • Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
  • Write balanced equations wherever required. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions 5 × 1 = 5 marks
1.
On electrolysis of a molten ionic hydride, hydrogen is liberated at the:
  • A.cathode
  • B.anode
  • C.both electrodes
  • D.neither electrode
2.
The H–O–H bond angle in water is about:
  • A.90°
  • B.104.5°
  • C.120°
  • D.180°
3.
Washing soda used to soften water is:
  • A.NaHCO3
  • B.Na2CO3
  • C.NaCl
  • D.NaOH
4.
Interstitial hydrides are formed mainly by:
  • A.s-block metals
  • B.p-block non-metals
  • C.many d- and f-block metals
  • D.noble gases
5.
Compared with ordinary water, heavy water has a:
  • A.lower boiling point
  • B.higher density
  • C.lower density
  • D.stronger smell
Section B — Short Answer (2 marks) 3 × 2 = 6 marks
6.
Distinguish between temporary and permanent hardness of water.
7.
Why does ice float on water?
8.
What is an interstitial hydride? Give one use.
Section C — Short Answer (3 marks) 2 × 3 = 6 marks
9.
Describe the ion-exchange resin method for obtaining demineralised water.
10.
Compare ionic, covalent and metallic hydrides with one example each.
Section D — Long Answer (5 marks) 1 × 5 = 5 marks
11.
Explain the causes of hard water and describe two methods each for removing temporary and permanent hardness with equations.

Answer Key

Section A — Multiple Choice Questions
  1. (B) anode
  2. (B) 104.5°
  3. (B) Na2CO3
  4. (C) many d- and f-block metals
  5. (B) higher density
Section B — Short Answer (2 marks)
  1. Temporary hardness is due to bicarbonates of Ca and Mg and is removed by boiling; permanent hardness is due to chlorides and sulphates of Ca and Mg and is not removed by boiling.
  2. In ice the molecules form an open, cage-like hydrogen-bonded network with more empty space, so ice is less dense than liquid water and floats.
  3. It is a hydride in which hydrogen atoms occupy the interstitial holes of a d- or f-block metal lattice, often non-stoichiometric; such hydrides are used to store hydrogen.
Section C — Short Answer (3 marks)
  1. Water is passed first through a cation-exchange resin that replaces Ca2+/Mg2+/Na+ with H+, then through an anion-exchange resin that replaces Cl−/SO42− with OH−. The H+ and OH− combine to form water, leaving demineralised water; the resins are regenerated with acid and alkali.
  2. Ionic hydrides (NaH) are non-volatile solids with H−; covalent hydrides (CH4) are volatile molecular species; metallic hydrides (TiH1.7) are non-stoichiometric solids with H in lattice holes used to store hydrogen.
Section D — Long Answer (5 marks)
  1. Hardness is caused by dissolved Ca2+ and Mg2+ salts. Temporary hardness (bicarbonates) is removed by (i) boiling, Ca(HCO3)2 → CaCO3↓ + H2O + CO2, and (ii) Clark's method, Ca(HCO3)2 + Ca(OH)2 → 2CaCO3↓ + 2H2O. Permanent hardness (chlorides/sulphates) is removed by (i) washing soda, CaCl2 + Na2CO3 → CaCO3↓ + 2NaCl, and (ii) the zeolite process, Na2Z + Ca2+ → CaZ + 2Na+, with the resin regenerated by brine.
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