JEE Chemistry Hydrogen MCQs Set 15

Answer: (a) 4

Explanation:
1. Tritium is \( \ce{^{3}_{1}H} \).
2. It has 1 proton, 2 neutrons and 1 electron.
3. Total = 1 + 2 + 1 = 4.

Teacher's Note:
1. Add all three kinds of particles, not only the nucleons.

Answer: (c) Electron configuration

Explanation:
1. The three isotopes have the same atomic number, so each has one electron in the 1s orbital.
2. Mass number and nuclear radius differ, and reactivity differs slightly because of different bond energies.

Teacher's Note:
1. Isotopes share electron configuration, not mass.

Answer: (d) Helium

Explanation:
1. Hydrogen forms hydrides with sodium on heating.
2. Noble gases such as helium form no compounds with hydrogen.

Teacher's Note:
1. Noble gases are chemically inert.

Answer: (a) \( \ce{F2} \)

Explanation:
1. Fluorine is the most electronegative and reacts explosively with hydrogen even in the dark.
2. The reactivity order is F2 > Cl2 > Br2 > I2.

Teacher's Note:
1. Reactivity falls down the halogen group.

Answer: (c) \( \ce{B2H6} \)

Explanation:
1. \( \ce{NH3} \) and \( \ce{PH3} \) have lone pairs (electron rich).
2. \( \ce{C2H6} \) is electron precise.
3. \( \ce{B2H6} \) has 12 valence electrons for 8 bonds and so uses 3-centre 2-electron bonds: it is electron deficient.

Teacher's Note:
1. Group 13 hydrides are electron deficient.

Answer: (c) Azane

Explanation:
1. IUPAC names for hydrides of group 15 elements end in -ane: \( \ce{NH3} \) is azane, \( \ce{PH3} \) phosphane.

Teacher's Note:
1. Learn azane, phosphane, arsane, stibane.

Answer: (d) All of these

Explanation:
1. Permutit, \( \ce{Na2Al2Si2O8.xH2O} \), is made by fusing soda ash, alumina and silica together.

Teacher's Note:
1. Permutit is a hydrated sodium aluminium silicate.

Answer: (c) \( \ce{H2O2} \)

Explanation:
1. \( \ce{BaO2 + H2O + CO2 -> BaCO3 + H2O2} \).
2. Insoluble \( \ce{BaCO3} \) is filtered off, leaving hydrogen peroxide solution.

Teacher's Note:
1. Carbon dioxide replaces sulphuric acid in this method.

Answer: (b) 300 mL

Explanation:
1. 20 volume means 1 mL of the solution gives 20 mL of \( \ce{O2} \) at STP.
2. Volume of \( \ce{O2} \) = 15 x 20 = 300 mL.

Teacher's Note:
1. Volume strength is mL of O2 per mL of solution.

Answer: (b) 6%

Explanation:
1. Normality = 20/5.6 = 3.57 N.
2. Mass per litre = 3.57 x 17 = 60.7 g, which is about 6% w/v.

Teacher's Note:
1. 100 volume is 30% and 20 volume is about 6%.

Answer: (b) \( \ce{PbS} \)

Explanation:
1. \( \ce{PbS + 4H2O2 -> PbSO4 + 4H2O} \).
2. \( \ce{KMnO4} \) and \( \ce{MnO2} \) are reduced by \( \ce{H2O2} \), and \( \ce{KCl} \) is not affected.

Teacher's Note:
1. This reaction is used to restore old paintings.

Answer: (c) \( \ce{Al4C3} \)

Explanation:
1. \( \ce{Al4C3 + 12D2O -> 4Al(OD)3 + 3CD4} \).
2. \( \ce{Mg3N2} \) would give \( \ce{ND3} \), \( \ce{CaC2} \) gives \( \ce{C2D2} \) and \( \ce{Ca3P2} \) gives \( \ce{PD3} \).

Teacher's Note:
1. Al4C3 is a methanide.

Answer: (c) Reactivity

Explanation:
1. D2 has a stronger bond (higher bond dissociation enthalpy) than H2.
2. Its physical constants such as latent heats and boiling point are higher, while its chemical reactivity is lower.

Teacher's Note:
1. Heavier isotope means stronger bond and slower reaction.

Answer: (b) 1 : 2 : 3

Explanation:
1. At the same T and P, density is proportional to molar mass.
2. Molar masses are 2, 4 and 6, so the ratio is 1 : 2 : 3.

Teacher's Note:
1. Use d = PM/RT.

Answer: (b) I, II and III

Explanation:
1. Conc. \( \ce{H2SO4} \) and dil. \( \ce{HNO3} \) act as oxidising agents and give \( \ce{SO2} \) or nitrogen oxides instead of \( \ce{H2} \).
2. Pure zinc reacts extremely slowly because no galvanic cell is set up, so III is also unsuitable.

Teacher's Note:
1. Impure granulated zinc works better.

Answer: (b) Electrolysis of warm aqueous barium hydroxide between nickel electrodes

Explanation:
1. NCERT: high-purity dihydrogen is obtained by electrolysing warm aqueous \( \ce{Ba(OH)2} \) solution between nickel electrodes.

Teacher's Note:
1. Pure water is a poor conductor.

Answer: (c) \( \ce{Zn^{2+}} \)

Explanation:
1. \( \ce{Zn^{2+}} \) has a very negative reduction potential, much lower than that of \( \ce{H+} \).
2. Hydrogen can reduce \( \ce{Cu^{2+}} \), \( \ce{Ag+} \) and \( \ce{Fe^{3+}} \), which lie above it in the electrochemical series.

Teacher's Note:
1. Metals above hydrogen in the series cannot be displaced by it.

Answer: (b) Basic

Explanation:
1. \( \ce{NaH + H2O -> NaOH + H2} \).
2. The strong base \( \ce{NaOH} \) is formed.

Teacher's Note:
1. Saline hydrides react violently with water.

Answer: (a) Dissolved sodium salts

Explanation:
1. Permutit exchanges \( \ce{Ca^{2+}} \) and \( \ce{Mg^{2+}} \) for \( \ce{Na+} \).
2. The softened water therefore contains dissolved sodium salts.

Teacher's Note:
1. Permutit removes hardness ions, not all ions.

Answer: (b) Calgon process

Explanation:
1. Calgon, sodium hexametaphosphate, forms a soluble complex with \( \ce{Ca^{2+}} \) and \( \ce{Mg^{2+}} \): \( \ce{2CaSO4 + Na4[Na2(PO3)6] -> Na2[Ca2(PO3)6] + 2Na2SO4} \).
2. Baeyer's, Serpeck's and Hoope's processes are used for aluminium.

Teacher's Note:
1. Calgon is the commercial name for sodium hexametaphosphate.

Answer: (b) \( \ce{-COOH} \)

Explanation:
1. A cation exchange resin has acidic groups such as \( \ce{-COOH} \) or \( \ce{-SO3H} \).
2. They exchange \( \ce{H+} \) for \( \ce{Ca^{2+}} \) and \( \ce{Mg^{2+}} \).

Teacher's Note:
1. Cation resin has acid groups and anion resin has basic groups.