# 10.15 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.

(a) Nitrates-

Alkali and alkaline earth metal nitrates are soluble in water. Down the group thermal stability of nitrates increases. Nitrates of alkaline and alkali metals give corresponding nitrites except for lithium nitrate, it gives lithium oxides.

$4LiNO_{3}\rightarrow 2Li_{2}O+4NO_{2}+O_{2}$

$NaNO_{3}\rightarrow 2NaNO_{2}+O_{2}$

$2M(NO_{3})_{2}\overset{\Delta }{\rightarrow}2MO+4NO_{2}+O_{2}$   [ M = Be, Mg, Ca, Sr, Ba]

(b) Carbonates-

Alkaline earth metal carbonates decompose on heating gives carbon dioxide and oxide. On the other hand carbonates of alkali metals are stable towards heat. The solubility of carbonates increases down the group in alkali metals (except $Li_{2}CO_{3}$) . But carbonates of alkaline earth metals are insoluble in water.

(c)Sulphate-

thermal stability is good for both alkali and alkaline earth metals. Alkali metal sulphates are more soluble in water than alkaline earth metals. Solubility decrease down the group from $CaSO_{4}$ to $BaSO_{4}$. sulphate of Be and Mg are readily soluble in water.

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