Question

When sodium hydroxide reacts with aluminium metal:
A. Sodium aluminate and water gas are formed.
B. Sodium aluminate and hydrogen gas are formed.
C. No reaction
D. Can’t say

Answer 1

Hint: Sodium hydroxide is a strong base and aluminium acts as a Lewis acid as it has vacant orbitals to accept or gain electrons. It also acts as metal and can release electrons (acting as Lewis base too). Thus, the nature of aluminium is overall amphoteric and it lies above hydrogen in the electrochemical series too.

Complete step by step answer:
When sodium hydroxide is made to react with aluminium metal, the following reaction takes place:
$2NaOH + 2Al + 2{H_2}O \to 2NaAl{O_2} + 3{H_2}$
Thus, we can see that sodium aluminate is formed in the product with a rigorous release of hydrogen.
This procedure is the general process employed in the industries for the production of sodium aluminate. Sodium aluminate is manufactured by the dissolution of aluminium hydroxide in a caustic soda (\[NaOH\] ) solution. Aluminium hydroxide (gibbsite) is prepared by dissolving aluminium in 20–25% aqueous \[NaOH\] solution at a temperature near the boiling point. The use of more concentrated \[NaOH\] solutions leads to a partial solid product.

So, the correct answer is Option B .

Note:
The process must be carried out in steam-heated vessels of nickel or steel, and the aluminium hydroxide should be boiled with approximately 50% aqueous caustic soda until a pulp forms. The final mixture has to be poured into a cooling tank where a solid mass containing about 70% \[NaAl{O_2}\] then forms. After being crushed, this product is dehydrated in a rotary oven. The resulting product contains 90% \[NaAl{O_2}\] and 1% water, together with 1% free \[NaOH\].