Question

What happens when sodium meta aluminate is diluted with water?

• A. Pure alumina is obtained.
• B. Impure aluminium ore is obtained.
• C. A precipitate of aluminium hydroxide is obtained.
• D. Aluminium oxide is formed.

Answer 1

The correct option is C

A precipitate of aluminium hydroxide is obtained.

Bauxite ore is finely ground and heated under pressure with concentrated caustic soda solution at ${150}^{0}C$ to obtain sodium meta-aluminate. The following reaction is as follows:

$\underset{Bauxite}{A{l}_2{O}_3.2H_{2}O}$ $+$ $2NaOH$ $\stackrel{{150}^{0}C}{\to }$ $2NaAl{O}_2$ $+$ $\underset{sodiummetaaluminate}{3H_{2}O}$

On diluting sodium meta-aluminate with water, aluminium hydroxide precipitate is obtained.

$NaAl{O}_2+2H_{2}O\to NaOH+Al(OH{)}_3\downarrow$

The precipitate is filtered, washed, dried and ignited at ${1000}^{0}C$ to get alumina.

$2Al(OH{)}_3\to A{l}_2{O}_3+3H_{2}O$