Question

Compare the solubility and thermal stability of the following compounds of the alkali metals with those of the alkaline earth metals. 

(i) Nitrates 

(ii) Carbonates 

(iii) Sulphates. 

Answer 1

Thermal stability: -
Carbonates: - The carbonates of alkali metals except lithium carbonate are stable towards heat. The carbonates of alkaline earth metals and Lithium carbonate decompose on heating to form oxides with the evolution of CO2.
Li₂CO₃ → Li₂O +CO₂ MgCO₃ → MgO + CO₂ Na₂CO₃ → No action 

Nitrates: - Nitrates of alkali metal except Lithium nitrate on heating forms nitrites with the evolution of oxygen. NaNO₃ → Na2O + O2. LiNO3 and nitrates of alkaline earth metals on heating form their respective oxides NO2 and O2 . 2LiNO3 → Li2O + 2NO2 + O2 2Ca (NO3)2→ 2CaO + 4NO2 + O2 

Sulphates: - The sulphates of both alkali and alkaline earth metals are thermally stable.