Question

Aluminium vessels should not be washed with materials containing washing soda because :

• A. washing soda is expensive
• B. washing soda is easily decomposed
• C. washing soda reacts with aluminium to form insoluble aluminium oxide
• D. washing soda reacts with aluminium to form soluble aluminate

Answer 1

Answer: (D)

Aluminium vessels should not be washed with materials containing washing soda since washing soda reacts with aluminium to form soluble aluminate. Under normal circumstances, aluminum does not react with water, as an impermeable protective layer composed of aluminum hydroxide either forms within seconds or is already in place. With the addition of sodium hydroxide, the formation of a protective layer is prevented. With the production of aluminates $\left[Al\right(OH{)}_4^{-}]$, the amphoteric (capable of acting as either an acid or a base) aluminum hydroxide $Al(OH{)}_3$ goes in solution.

The reaction is as follows:

$2Al+6H_{2}O\to 2Al(OH{)}_3+3H_2$

$Al(OH{)}_3+NaOH\to N{a}^{+}+[Al(OH{)}_4{]}^{-}$