JEE Main 2022 · 25 July · evening · Single correct · +4 / −1
High purity (> 99.95%) dihydrogen is obtained by :
- (a) reaction of zinc with aqueous alkali.
- (b) electrolysis of acidified water using platinum electrodes.
- (c) electrolysis of warm aqueous barium hydroxide solution between nickel electrodes.
- (d) reaction of zinc with dilute acid.
Answer and solution
Answer (c) electrolysis of warm aqueous barium hydroxide solution between nickel…
Solution
Chemistry ma’am · 3 steps
For the purest hydrogen, do not use a metal; electrolyse warm barium hydroxide with nickel electrodes.
- Zinc methods. Zinc gives H₂ with both dilute acid and aqueous alkali, so these are convenient lab methods. Commercial zinc is impure, though, and its impurities pass into the gas as traces of other gases, so the purity is limited.
- Electrolysis route. Electrolysing water uses no metal, so it gives much purer gas. Hydrogen forms at the cathode: 2H₂O + 2e⁻ → H₂ + 2OH⁻.
Method Where it is used Purity of H₂ (a) Zn + aqueous alkali laboratory ordinary (b) Acidified water, Pt electrodes general preparation good, but not the textbook high-purity method (c) Warm aqueous Ba(OH)₂, Ni electrodes high-purity preparation above 99.95% (d) Zn + dilute acid laboratory ordinary - So. High purity dihydrogen (above 99.95%) comes from electrolysing warm aqueous Ba(OH)₂ between nickel electrodes. The answer is (c).
The idea to keep. Remember the hydrogen methods by their purpose: zinc with acid or alkali in the lab, acidified water electrolysis in general, and warm Ba(OH)₂ with Ni electrodes for above 99.95% purity.
Answer from the NTA final answer key. Solution by PrepWiser.