JEE Chemistry Hydrogen MCQs Set 11

Chemistry Objective Questions and Answers: Hydrogen

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Multiple Choice Questions

Question 1: The strength of an 11.2 volume solution of H₂O₂ is (molar masses: H = 1 g mol⁻¹, O = 16 g mol⁻¹):
(a) 1.7%
(b) 34%
(c) 13.6%
(d) 3.4%
Show Answer & Explanation

Answer: (d) 3.4%

Explanation:
1. 11.2 volume means 1 mL of the solution gives 11.2 mL of O₂ at STP, i.e. 1 L gives 11.2 L.
2. 2H₂O₂ → 2H₂O + O₂: 68 g of H₂O₂ gives 22.4 L of O₂, so 11.2 L of O₂ needs 34 g of H₂O₂.
3. 34 g in 1000 mL gives a strength of 3.4% (w/v).

Teacher's Note:
1. Volume strength = 11.2 × molarity; 11.2 V corresponds to 1 M, that is 34 g per litre or 3.4%.

Question 2: The correct statements among the following are: (1) Saline hydrides produce H₂ gas when reacted with H₂O. (2) Reaction of LiAlH₄ with BF₃ leads to B₂H₆. (3) PH₃ and CH₄ are electron-rich and electron-precise hydrides respectively. (4) HF and CH₄ are called molecular hydrides.
(a) (1), (2), (3) and (4)
(b) (1), (2) and (3) only
(c) (3) and (4) only
(d) (1), (3) and (4) only
Show Answer & Explanation

Answer: (a) (1), (2), (3) and (4)

Explanation:
1. Ionic hydrides react with water: H⁻ + H₂O → H₂ + OH⁻, so (1) is correct.
2. 3LiAlH₄ + 4BF₃ → 2B₂H₆ + 3LiF + 3AlF₃, so (2) is correct.
3. PH₃ has a lone pair on P (electron-rich) while CH₄ has exactly the electrons needed for its bonds (electron-precise), so (3) is correct.
4. HF and CH₄ are discrete molecules, so (4) is also correct.

Teacher's Note:
1. Classify hydrides as ionic (saline), covalent/molecular (electron-deficient, precise, rich) and metallic (interstitial).

Question 3: The metal that gives hydrogen gas upon treatment with both acid as well as base is:
(a) magnesium
(b) mercury
(c) zinc
(d) iron
Show Answer & Explanation

Answer: (c) zinc

Explanation:
1. Zn + 2HCl → ZnCl₂ + H₂.
2. Zn + 2NaOH → Na₂ZnO₂ + H₂, because zinc is amphoteric.

Teacher's Note:
1. Amphoteric metals such as Zn and Al liberate H₂ with both acids and alkalis.

Question 4: The temporary hardness of a water sample is due to compound X. Boiling this sample converts X to compound Y. X and Y, respectively, are:
(a) Mg(HCO₃)₂ and Mg(OH)₂
(b) Ca(HCO₃)₂ and Ca(OH)₂
(c) Mg(HCO₃)₂ and MgCO₃
(d) Ca(HCO₃)₂ and CaO
Show Answer & Explanation

Answer: (a) Mg(HCO₃)₂ and Mg(OH)₂

Explanation:
1. Temporary hardness is due to the hydrogen carbonates of Mg and Ca.
2. On boiling, Mg(HCO₃)₂ gives the insoluble hydroxide, Mg(OH)₂ (because MgCO₃ is relatively soluble), while Ca(HCO₃)₂ gives CaCO₃.
3. Of the given options, only the first pair is correct.

Teacher's Note:
1. Boiling removes temporary hardness: magnesium separates as Mg(OH)₂, calcium as CaCO₃.

Question 5: The isotopes of hydrogen are:
(a) deuterium and tritium only
(b) protium and deuterium only
(c) protium, deuterium and tritium
(d) tritium and protium only
Show Answer & Explanation

Answer: (c) protium, deuterium and tritium

Explanation:
1. Hydrogen has three isotopes of mass number 1, 2 and 3.
2. They are protium (¹H), deuterium (²H or D) and tritium (³H or T).

Teacher's Note:
1. All three, protium, deuterium and tritium, are isotopes of hydrogen.

Question 6: The reason for the temporary hardness of water is:
(a) Na₂SO₄
(b) CaCl₂
(c) NaCl
(d) Ca(HCO₃)₂
Show Answer & Explanation

Answer: (d) Ca(HCO₃)₂

Explanation:
1. Temporary hardness arises from soluble hydrogen carbonates of calcium and magnesium.
2. The chlorides and sulphates of Ca and Mg cause permanent hardness; the sodium salts do not cause hardness.

Teacher's Note:
1. Hydrogen carbonates give temporary hardness; chlorides and sulphates give permanent hardness.

Question 7: The chemical nature of hydrogen peroxide is:
(a) oxidising and reducing agent in both acidic and basic medium
(b) oxidising and reducing agent in acidic medium, but not in basic medium
(c) reducing agent in basic medium, but not in acidic medium
(d) oxidising agent in acidic medium, but not in basic medium
Show Answer & Explanation

Answer: (a) oxidising and reducing agent in both acidic and basic medium

Explanation:
1. As an oxidant: H₂O₂ + 2H⁺ + 2e⁻ → 2H₂O (acidic) and H₂O₂ + 2e⁻ → 2OH⁻ (basic).
2. As a reductant: H₂O₂ → O₂ + 2H⁺ + 2e⁻ (acidic) and H₂O₂ + 2OH⁻ → O₂ + 2H₂O + 2e⁻ (basic).

Teacher's Note:
1. H₂O₂ is both an oxidising and a reducing agent in acidic as well as basic media.

Question 8: The total number of isotopes of hydrogen and the number of radioactive isotopes among them, respectively, are:
(a) 2 and 1
(b) 3 and 2
(c) 2 and 0
(d) 3 and 1
Show Answer & Explanation

Answer: (d) 3 and 1

Explanation:
1. Hydrogen has three isotopes: protium, deuterium and tritium.
2. Only tritium is radioactive; its n/p ratio is 2, which is outside the stability range.

Teacher's Note:
1. Tritium (³H) is the only radioactive isotope of hydrogen.

Question 9: NaH is an example of:
(a) metallic hydride
(b) electron-rich hydride
(c) saline hydride
(d) molecular hydride
Show Answer & Explanation

Answer: (c) saline hydride

Explanation:
1. NaH is formed from an electropositive s-block metal and hydrogen.
2. It contains Na⁺ and H⁻ ions, so it is an ionic (saline) hydride.

Teacher's Note:
1. s-Block metals (except Be and Mg) form saline hydrides.

Question 10: The correct statements among the following regarding H₂ as a fuel are: I. It produces less pollutants than petrol. II. A cylinder of compressed dihydrogen weighs about 30 times more than a petrol tank producing the same amount of energy. III. Dihydrogen is stored in tanks of metal alloys like NaNi₅. IV. On combustion, the energy released per gram of liquid dihydrogen and LPG are 50 and 142 kJ respectively.
(a) I, II and III only
(b) II, III and IV only
(c) II and IV only
(d) I and III only
Show Answer & Explanation

Answer: (a) I, II and III only

Explanation:
1. H₂ burns to give only water, so it is pollution free: I is correct.
2. Compressed H₂ cylinders are heavy for the energy delivered: II is correct.
3. Metal alloys such as NaNi₅ store hydrogen: III is correct.
4. The values in IV are interchanged (H₂ gives about 142 kJ g⁻¹ and LPG about 50 kJ g⁻¹), so IV is incorrect.

Teacher's Note:
1. Dihydrogen has a much higher energy per gram than LPG or petrol.

Question 11: The hydride that is not electron deficient is:
(a) AlH₃
(b) B₂H₆
(c) SiH₄
(d) GaH₃
Show Answer & Explanation

Answer: (c) SiH₄

Explanation:
1. Hydrides of group 13 (AlH₃, B₂H₆, GaH₃) have fewer electrons than needed for normal two-centre bonds, so they are electron deficient.
2. SiH₄ is a group 14 hydride and is electron precise.

Teacher's Note:
1. Group 13 hydrides are electron deficient, group 14 electron precise and groups 15 to 17 electron rich.

Question 12: The volume strength of 1 M H₂O₂ is (molar mass of H₂O₂ = 34 g mol⁻¹), approximately:
(a) 16.8
(b) 22.4
(c) 11.35
(d) 5.6
Show Answer & Explanation

Answer: (c) 11.35

Explanation:
1. Volume strength = 11.2 × molarity = 11.2 × 1.
2. The value 11.2 is closest to 11.35 among the options.

Teacher's Note:
1. Volume strength of H₂O₂ = 11.2 × M.

Question 13: Very pure hydrogen (99.9%) can be made by which of the following processes?
(a) Reaction of methane with steam
(b) Mixing natural hydrocarbons of high molecular weight
(c) Electrolysis of water
(d) Reaction of salts like hydrides with water
Show Answer & Explanation

Answer: (d) Reaction of salts like hydrides with water

Explanation:
1. Methane/steam reforming and hydrocarbon cracking give hydrogen mixed with CO, CO₂ and other gases.
2. Ionic hydrides react with water to give H₂ of high purity, e.g. CaH₂ + 2H₂O → Ca(OH)₂ + 2H₂.

Teacher's Note:
1. Hydrolysis of ionic hydrides gives very pure H₂.

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