Question

State whether an aqueous solution of washing soda is acidic or alkaline? Give reason for your answer.

Answer 1

An aqueous solution of washing soda is alkaline, because sodium carbonate is a salt prepared from the reaction between a weak acid, carbonic acid (H₂CO₃), and a strong base, sodium hydroxide (NaOH). When sodium carbonate is dissolved in water, it gets hydrolysed to some extent and forms sodium hydroxide and carbonic acid

 Na₂CO₃(s) + 2H₂O(l)  → 2NaOH(aq) + H₂CO₃(aq)
 Sodium hydroxide, being a strong base, is fully ionised to give a large amount of hydroxide ions (OH^-), and carbonic acid, being a weak acid, is slightly ionised to form a small amount of hydrogen (H⁺) ions. Therefore, an aqueous solution contains more hydroxide ions than hydrogen ions, which makes the solution basic.