Vidaara.orgClass 11 · Chemistry
CodeVID-C11-09-CH-01
Chapter Assignment — Hydrogen
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
6 × 1 = 6 marks
1.
The most abundant element in the universe is:
- A.oxygen
- B.hydrogen
- C.helium
- D.carbon
2.
The isotope of hydrogen with one neutron is:
- A.protium
- B.deuterium
- C.tritium
- D.none
3.
Which is an interstitial (metallic) hydride?
- A.NaH
- B.CH4
- C.PdH0.6
- D.HCl
4.
Soft water lathers easily with soap because it has no:
- A.Na+ ions
- B.Ca2+/Mg2+ ions
- C.K+ ions
- D.Cl− ions
5.
Hydrogen peroxide is stored away from light because light:
- A.dissolves it
- B.speeds its decomposition
- C.colours it
- D.freezes it
6.
Heavy water has the formula:
- A.H2O
- B.D2O
- C.T2O
- D.H2O2
Section B — Short Answer (2 marks)
4 × 2 = 8 marks
7.
Why is hydrogen given a unique position in the periodic table?
8.
Write the reaction used in Clark's method for softening water.
9.
Give one reaction each in which H2O2 acts as an oxidising and as a reducing agent.
10.
State two advantages of dihydrogen as a fuel.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
11.
Describe the three types of hydrides with one example each.
12.
Explain the open-book structure of hydrogen peroxide with its key parameters.
Section D — Long Answer (5 marks)
2 × 5 = 10 marks
13.
Explain hard water, distinguishing temporary and permanent hardness, and describe how each is removed (with equations).
14.
Discuss dihydrogen as a fuel: its energy advantage, the hydrogen economy, fuel cells and the main challenges.
Answer Key
Section A — Multiple Choice Questions
- (B) hydrogen
- (B) deuterium
- (C) PdH0.6
- (B) Ca2+/Mg2+ ions
- (B) speeds its decomposition
- (B) D2O
Section B — Short Answer (2 marks)
- Because it shows properties of both alkali metals (one valence electron, forms H+) and halogens (diatomic, forms H−) and fits neither group perfectly.
- Ca(HCO3)2 + Ca(OH)2 → 2CaCO3↓ + 2H2O; the insoluble carbonate is filtered off.
- Oxidiser: 2Fe2+ + H2O2 + 2H+ → 2Fe3+ + 2H2O. Reducer: 2MnO4− + 5H2O2 + 6H+ → 2Mn2+ + 5O2 + 8H2O.
- It releases a very high energy per gram (about 143 kJ g−1) and its combustion produces only water, so it is non-polluting.
Section C — Short Answer (3 marks)
- Ionic/saline (NaH, CaH2): non-volatile solids containing H−. Covalent/molecular (CH4, NH3): volatile discrete molecules. Metallic/interstitial (PdH0.6, TiH1.7): hydrogen in metal lattice holes, often non-stoichiometric.
- H2O2 is non-planar; the two O–H bonds lie in two planes meeting at the O–O bond, like a half-open book. The gas-phase dihedral angle is about 111°, the O–O bond about 148 pm and the O–H bond about 95 pm.
Section D — Long Answer (5 marks)
- Hard water contains dissolved Ca2+/Mg2+ salts that form scum with soap. Temporary hardness (bicarbonates) is removed by boiling, Ca(HCO3)2 → CaCO3↓ + H2O + CO2, or Clark's method, Ca(HCO3)2 + Ca(OH)2 → 2CaCO3↓ + 2H2O. Permanent hardness (chlorides/sulphates) is removed by washing soda, CaCl2 + Na2CO3 → CaCO3↓ + 2NaCl, or by the zeolite/ion-exchange process, Na2Z + Ca2+ → CaZ + 2Na+, the resin being regenerated by brine.
- Dihydrogen releases about 143 kJ g−1 on combustion (2H2 + O2 → 2H2O), far more per gram than petrol, with only water as product. The hydrogen economy proposes storing and moving energy as hydrogen. In a fuel cell hydrogen and oxygen react electrochemically to give electricity directly and efficiently (only water as by-product), as used in spacecraft. The main challenges are the safe, compact storage of a light flammable gas and producing hydrogen cheaply without releasing CO2.
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