s - block Elements (Alkali and Alkaline Earth Metals)
The lightest metal among the following is:
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.
(i) Solubility
Nitrates, carbonates and sulphates of alkali metals are water soluble. On moving down the group, the solubility increases. This is because their lattice energies decreases more rapidly than their hydration energies.
Alkaline earth metal nitrates are water soluble. On moving down the group, their solubility decreases. This is because their hydration energies decreases more rapidly than their lattice energies.
Alkaline earth metal carbonates and sulphates have lower solubility than alkali metal carbonates and sulphates. The solubility of alkaline metal carbonates and sulphates decreases with decrease in hydration energy as we move down the group.
(ii) Thermal stability
Alkali and alkaline earth metal nitrates decompose on heating. On heating alkali metal (Na, K, Rb and Cs) decompose to form metal nitrites and oxygen.
$$\displaystyle 2MNO_3 \xrightarrow {heat} 2MnO_2+O_2 $$
Alkaline earth metal nitrates decompose on heating to give metal oxide, nitrogen dioxide and oxygen.
$$\displaystyle 2M(NO_3)_2 \xrightarrow {heat} 2MO + 4NO_2+O_2 (M=Be, Mg, Ca, Sr, Ba)$$
Lithium nitrate (like magnesium nitrate) decomposes to form metal oxide, nitrgen dioxide and oxygen.
$$\displaystyle 4LiNO_3 \xrightarrow {Heat} 2Li_2O +4NO_2+O_2 $$
This is because small sized Li+ ion cannot stabilize nitrate ion.
Alkaline earth metal carbonates have less stability towards heat and decompose to carbon dioxide.
$$\displaystyle MCO_3 \rightarrow MO + CO_2 $$
On moving down the group, the stability of alkaline earth metal carbonates increases. Because of diagonal relationship, lithium carbonate decomposes similar to magnesium carbonate.
$$\displaystyle Li_2CO_3 \xrightarrow {heat} Li_2O + CO_2 $$
Other alkali metal carbonates being stable to heat do not decompose.
On heating, alkaline earth metal sulphates decompose to form $$\displaystyle SO_3 $$
$$\displaystyle MSO_4 \xrightarrow {heat} MO+SO_3 $$
On moving down the group, the electropositive characteer and the thermal stability of alkaline earth metal sulphates increases.
Except $$\displaystyle Li_2SO_4 $$, the alkali metal sulphates are stable and do not decompose easily.
$$\displaystyle Li_2SO_4 $$ decomposes like $$\displaystyle MgSO_4 $$ to give $$\displaystyle SO_3 $$
$$\displaystyle Li_2SO_4 \xrightarrow {heat} Li_2O + SO_3 $$
$$\displaystyle MgSO_4 \xrightarrow {heat} MgO + SO_3 $$
The lightest metal among the following is:
Size of hydrated ion of $$Li^+ and Be^{2+} $$ is :
Compare the solubility and thermal stability of alkali metals carbonates with those of the alkaline earth metals nitrates.
Which of the following oxides is most acidic in nature?
The correct order of solubility of the following compound in water is:
The hydroxides and carbonates of sodium and potassium are easily soluble in water while the corresponding salts of magnesium and calcium are sparingly soluble in water. Explain?
$$CaCl_2$$ is preferred over $$NaCl$$ for clearing ice on roads on particularly in very cold countries. This is because:
Alkaline earth metals are better reducing agents than alkali metals.
Which of the following groups of elements have chemical properties that are most similar :
If $$X$$ and $$Y$$ are the second ionisation potentials of alkali and alkaline earth metals of same period, then :