Chemistry Class 11 NCERT Solutions: Chapter 10 the s Block Elements Part 5

Q: 15. Compare the solubility and thermal stability of the following compounds of the alkali metals with those of the alkaline earth metals.

(A) Nitrates

(B) Carbonates

(C) Sulphates.

Answer:

(i) Nitrates

Thermal stability

Nitrates of alkali metals, except Equation decompose on strong heating to form nitrites.

Equation

Equation on decomposition, given oxide.

Equation

Similar to lithium nitrate, alkaline earth metal nitrates also decompose to give oxides

Equation

As we move down group 1 and group 2, the thermal stability of nitrate increases.

Solubility

Nitrates of both group 1 and group 2 metals are soluble in water.

(ii) Carbonates

Thermal stability

The carbonates of alkali metals are stable towards heat. However, carbonate of lithium, when heated, decomposes to form lithium oxide. The carbonates of alkaline earth metals also decompose on heating to form oxide and carbon dioxide.

Equation

Equation

Equation

Solubility

Carbonates of alkali metals are soluble in water with the exception of Equation . Also, the solubility increases as we move down the group.

Carbonates of alkaline earth metals are insoluble in water.

(iii) Sulphates

Thermal stability

Sulphates of both group 1 and group 2 metals are stable towards heat.

Solubility

Sulphates of alkali metals are soluble in water. However, sulphates of alkaline earth metals show varied trends.

Equation Fairly soluble

Equation Soluble

Equation Sparingly soluble

Equation Insoluble

Equation Insoluble

In other words, while moving down the alkaline earth metals, the solubility of their sulphates decreases.

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