Aqueous ammonia is used instead of an aqueous | vedclass

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Question

(B) $Al(OH)_3$ is an amphoteric hydroxide. When $NaOH$ (a strong base) is added in excess,it reacts with $Al(OH)_3$ to form a soluble complex,$[Al(OH)

Vedclass · Accepted Answer

$NaOH$ forms $[Al(OH)_4]^-$ ions.

Vedclass · Answer

(B) $Al(OH)_3$ is an amphoteric hydroxide. When $NaOH$ (a strong base) is added in excess,it reacts with $Al(OH)_3$ to form a soluble complex,$[Al(OH)_4]^-$,which prevents the precipitation of $Al^{+3}$ ions. $Al(OH)_3 + OH^- \rightarrow [Al(OH)_4]^-$. Since aqueous ammonia is a weak base,it provides a limited concentration of $OH^-$ ions,which is sufficient to precipitate $Al(OH)_3$ but not strong enough to dissolve the precipitate by forming the complex.

Aqueous ammonia is used instead of an aqueous solution of $NaOH$ to precipitate $Al^{+3}$ ions as $Al(OH)_3$ because:

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