Which salt among the following can you use to distinguish between sodium hydroxide and ammonium hydroxide?

Copper sulphate

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Ferrous sulphate

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Ferric chloride

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Zinc sulphate

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Solution

The correct option is A Copper sulphate
The results of the reaction of copper sulphate $({C u S O}_{4})$ with NaOH and ${N H}_{4} O H$ are summarised in the given table:

Treatment with NaOH Treatment with ${N H}_{4} O H$

${C u S O}_{4}$ forms a precipitate of ${C u (O H)}_{2}$ that is insoluble in excess NaOH. ${C u S O}_{4}$ forms a precipitate that is soluble in excess ${N H}_{4} O H$ .

$C u S O_{4} + 2 N a O H \to N a_{2} S O_{4} + C u {(O H)}_{2} (p p t .)$ $C u S O_{4} + 2 N H_{4} O H \to C u {(O H)}_{2} + {(N H_{4})}_{2} S O_{4}$
But ${C u (O H)}_{2}$ further reacts with ${N H}_{4} O H$ to form a water soluble compound:

$C u {(O H)}_{2} + 4 N H_{4} O H \to [C u {(N H_{3})}_{4}] {(O H)}_{2}$

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Treatment with NaOH	Treatment with ${N H}_{4} O H$
${C u S O}_{4}$ forms a precipitate of ${C u (O H)}_{2}$ that is insoluble in excess NaOH.	${C u S O}_{4}$ forms a precipitate that is soluble in excess ${N H}_{4} O H$ .
$C u S O_{4} + 2 N a O H \to N a_{2} S O_{4} + C u {(O H)}_{2} (p p t .)$	$C u S O_{4} + 2 N H_{4} O H \to C u {(O H)}_{2} + {(N H_{4})}_{2} S O_{4}$ But ${C u (O H)}_{2}$ further reacts with ${N H}_{4} O H$ to form a water soluble compound: $C u {(O H)}_{2} + 4 N H_{4} O H \to [C u {(N H_{3})}_{4}] {(O H)}_{2}$