Question

A metal is soft and can be cut with knife. It catches fire when poured over water. When its salt is electrolysed , we get alkali solution and two gases in the ratio 1:1. Explain the reaction and give chemical equations.

Answer 1

1. The metal is Sodium. It has atomic number 11 and the electronic configuration is [Ne]3s¹.
2. Due to the presence of only one electron in the valence shell,metallic bonds are weak and therefore,it can be cut by a knife.
3. When water is poured on sodium metal,following reaction occurs :

2Na(s) + 2H₂O(l) $\to$ 2NaOH(aq) + H₂ + heat
As heat is released in the reaction,sodium metal catches fire and as hydrogen gas is flammable,the fire is uncontrollable.

4. When the salt solution of NaCl in water is electrolysed,NaOH is formed releasing Cl₂ at anode and H₂ at cathode. As shown :
Anode :
2 Cl^- $\to$ Cl₂ + 2 e^-
Cathode :
2 H⁺ + 2e^- $\to$ 2H₂