First slide

Uses of Boron & Aluminium

Question

Which statement is not rue about potash alum?

Moderate

A

Its empirical formula is KAl(SO₄)₂.12H₂O
B

Its aqueous solution is basic in nature,
C

It is used in dyeing industries
D

On heating it melts and loses its water of crystallization

Solution

$\large I)Molecular\,Formula\,of\,potash\,alum\,is\,{K_2}S{O_{4\,}}A{l_2}{(S{O_4})_3}.24{H_2}O\,\left( {OR} \right)\,{K_2}A{l_2}{\left( {S{O_4}} \right)_4}.24{H_2}O\$
$\large Emperical\,formula\,of\,potash\,alum\,is,\,KAl{\left( {S{O_4}} \right)_2}.12{H_2}O$
$\large II)\,\,{K_2}S{O_{4\,}}A{l_2}{(S{O_4})_3}.24{H_2}O\,\xrightarrow{{{H_2}O}}\mathop {2{K^ + }}\limits_{Cation\,\,\,of\,strong\,base} + \mathop {2A{l^{ + 3}}}\limits_{Cation\,\,\,of\,weak\,base} + \mathop {4SO_4^{ - 2}}\limits_{Anion\,\,of\,\,strong\,acid}$
Alum undergo cationic hydrolysis.Cation of weak base and anion of weak acid only undergoing hydrolysis.
$\large 2A{l^{ + 3}} + 6{H_2}O \to 2Al{(OH)_3} + \mathop {6{H^ + }}\limits_{Acid}$
Due to the liberation of H⁺ ion the aqueous solution shows acidic nature and not basic nature.
III) It is used in dyeing industry,
It is used in the purification of water,
It is used in tanning of leather.
$\large IV)\,\,{K_2}S{O_{4\,}}A{l_2}{(S{O_4})_3}.24{H_2}O\,\xrightarrow{\Delta }{K_2}S{O_4}.A{l_2}{(S{O_4})_3} + 24{H_2}O$
On heating it loses water of crystallisation.

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