Question

Select the incorrect statement.

• A. Sodium peroxide dissolves in cold water giving $H_2{O}_2$ and $NaOH$
• B. Both $LiN{O}_3$ and $NaN{O}_3$ on heating separately decompose and each liberates two gases $N{O}_2$ and $O_2$
• C. Sodium react vigorously with water than Lithium
• D. Alkali metals are prepared only by the electrolysis of their fused chlorides

Answer 1

The correct option is B Both $LiN{O}_3$ and $NaN{O}_3$ on heating separately decompose and each liberates two gases $N{O}_2$ and $O_2$

1. Sodium peroxide $(N{a}_2{O}_2$) is pale yellow in colour. It is a powerful oxidant. It reacts with water to give sodium hydroxide and hydrogen peroxide.
$N{a}_2{O}_2+2H_{2}O\to 2NaOH+H_2{O}_2$

2. Sodium nitrate decompose to sodium nitrite and oxygen while lithium nitrate decompose more readily forming the oxides. This is due to the relative small size of lithium which makes it more polarising and favours the formation of oxide.
$4LiN{O}_3\stackrel{\Delta }{\to }2L{i}_{2}O+4N{O}_2+O_2$; $2NaN{O}_3\stackrel{\Delta }{\to }2NaN{O}_2+O_2$

3. Lithium has most negative $E^o$ than sodium but it react less vigorous with water tham sodium because sodium has melting point than lithium and it melt on the surface of water and expose larger surface area and react vigourously and catches fire.

4. Aqueous salt solution are not used for the electrolysis of alkali metals because they are more electropositive than hydrogen ion due to which hydrogen ions will get discharge preferentially to form hydrogen gas. So only fused salts are used in electrolysis for the preparation of alkali metals.