S-Block Elements Test - 9

Sodium sulphide is oxidised to sodium thiosulphate in the presence of both O₂ and H₂O.
2Na₂S + 2O₂ + H₂O → Na₂S₂O₃ + 2NaOH
In a concentrated solution of an alkali metal in NH₃, the unpaired electrons pair up together and the solution becomes diamagnetic, and the conductivity of the solution decreases considerably. The colour of the solution changes from blue to bronze.
K₂CO₃ cannot be prepared by Solvay process as its hydrogen carbonate is water soluble.
Potassium is more reactive than sodium because of its lower ionisation potential and a more negative value of its reduction potential.
Hence, statement (1) is incorrect, whereas all other statements are correct.

Ba(NO₃)₂ + Na₂SO₄ → BaSO₄ + 2NaNO₃
The Barium sulphate formed is an insoluble salt and does not dissolve in the blood plasma.

As the size of the cation decreases and the extent of polarisation increases, the covalent character increases and the stability decreases.

The atom becomes larger on descending the group, so the bonds are weaker (metallic bond), the cohesive energy decreases and accordingly, the melting point also decreases.

NOTE: Although the ionization energy also decreases down the group and so does the hydration energy when salts of these metals are added to water, but these are not the factors affecting the melting points of the metals.

The solubility of the alkaline earth metal hydroxides increases down the group as the solubility product increases.\

Be(OH)₂ (K_sp= 1.6 × 10^-26)
Ba(OH)₂ (K_sp = 5.4 × 10^-3)