Question

Why potassium and cold water are not used to prepare hydrogen in laboratory

Answer 1

Potassium and cold water are not used to prepare hydrogen in laboratory because:

1. Potassium is highly reactive metal and it reacts violently with cold water.
2. Potassium , when dropped in beaker containing water, we can see that potassium moves in water making hissing sound and catches fire easily.

chemical reaction:
2K + 2H2O ---> 2KOH + H2

Potassium reacts with water to form potassium hydroxide and hydrogen gas.
A lot of heat is produced in this reaction.
This heat burns the Hydrogen gas as well as potassium metal..
The burning of H2 gas causes little explosion.

Hence to avoid this, potassium is always stored in Kerosene.

Answer 2

Potassium and Cold Water are not used for the Laboratory Preparation of the Hydrogen because Potassium vigorously reacts with cold water and the heavy around of the Heat is evolved during this process since the reaction is Exothermic in nature.

Similarly, Sodium also reacts thus they are not used for the Laboratory preperation of the Hydrogen.

If it will be used in the Laboratory Preparation then due to the evolution of the Heat, it may cause a fatal to the person.

But when it reacts, reaction is as follows,

2K + 2H₂O ---------- 2KOH + H₂

Hope it helps.