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Question
A salt X when dissolved in distilled water gives a clear solution which turns red litmus blue. Explain the phenomenon.
Solution
As the aqueous solution of salt X turns red litmus blue, it must be basic in nature.
For example, an aqueous solution of sodium acetate salt is basic. Sodium acetate (CH3COONa) is a salt prepared from the reaction between a weak acid, acetic acid (CH3COOH), and a strong base, sodium hydroxide (NaOH). When sodium acetate is dissolved in water, it gets hydrolysed to some extent to form sodium hydroxide and acetic acid.
CH3COONa (s) + H2O(l) → NaOH(aq) + CH3COOH(aq)
Sodium hydroxide, being a strong base, is fully ionised to give a large amount of hydroxide ions (OH-), and acetic acid, being a weak acid, is slightly ionised to form a small amount of hydrogen (H+) ions. Therefore, the aqueous solution contains more hydroxide ions than hydrogen ions, which makes the solution basic.
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