Question

Which one of the following reactions does not result in the evolution of hydrogen gas?
1. Reaction of zinc metal with dilute sulphuric acid solution
2. Mixing water to Plaster of Paris
3. Heating zinc metal with sodium hydroxide solution
4. Reaction of potassium metal with water

Answer 1

Correct Answer - Option 2 : Mixing water to Plaster of Paris

The correct answer is Mixing water to Plaster of Paris.

• When plaster of Paris is mixed with water, it gets converted into gypsum.
  • CaSO₄.\(\frac {1} {2}\)H₂O + H₂O \(\longrightarrow\) CaSO₄.2H₂O, Hence it doesn't give hydrogen gas.

              (Plaster of Paris)  (Water)       (Gypsum)

• While heating of Gypsum at 373K results in Plaster of Paris.

• Metal + Dilute acid \(\longrightarrow\) Salt + Hydrogen, thus the reaction of zinc metal with dilute sulphuric acid solution would give hydrogen gas.
• Bases react with metals like zinc and aluminium which leads to the formation of zincate or aluminate along with the evolution of a gas.
  • 2NaOH + Zn \(\longrightarrow \) 2NaZnO₂ + H₂ (g)
• Metals react with water and produce a metal oxide and hydrogen gas.
  • 2K(s) + 2H₂O(l) \(\longrightarrow \) 2KOH(aq) + H₂ (g) + heat energy