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 sodium aluminate
(D) washing soda reacts with aluminium to form insoluble aluminium oxide

Answer 1

Write the molecular formula of washing soda and determine its properties. Then write the reaction which takes place when aluminium reacts with washing soda. Read each option and then find out which one is the best answer.

Complete step by step solution:
- Aluminium is a metal having the atomic number 13. Its electronic configuration is $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{1}}$.
- Washing soda is sodium carbonate, $N{{a}_{2}}C{{O}_{3}}$.
- Washing soda reacts with aluminium to form sodium aluminate.
- Normally, aluminium doesn’t react with water due to the presence of a thin impermeable protective layer of aluminium hydroxide, which is formed immediately when aluminium is exposed to water and it prevents the formation of aluminate salts.
$2Al+6{{H}_{2}}O\to 2Al{{\left( OH \right)}_{3}}+3{{H}_{2}}$
- When aluminium is washed using washing soda, aluminium hydroxide layer is easily dissolved and removed which makes aluminium undergo corrosion with water to form aluminate salts.
- The reactions taking place are first, washing soda reacts with water to form sodium hydroxide and carbon dioxide. Then sodium hydroxide reacts with aluminium to form sodium aluminate.
$N{{a}_{2}}C{{O}_{3}}+{{H}_{2}}O\to 2NaOH+C{{O}_{2}}$
$2NaOH+2Al+2{{H}_{2}}O\to 2Na\left[ Al{{\left( OH \right)}_{4}} \right]+3{{H}_{2}}$
- Due to the generation of aluminate salts, aluminium hydroxide solubilizes in the solution.
- Therefore, aluminium vessels should not be washed with materials containing washing soda because washing soda reacts with aluminium to form sodium aluminate.

- Therefore, the answer is option (C).

Note: Remember washing soda is sodium carbonate and baking soda is sodium bicarbonate. Aluminium reacts with water to form a thin layer of aluminium hydroxide. This property of aluminium is used in the passivation process of aluminium which increases the shelf –life of aluminium utensils.