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Methods to Form Lyophobic Colloids

A freshly pre...

Question

A freshly prepared saturated solution of a potassium salt produces a yellow precipitate with a highly concentrated solution of cobalt (II) chlorine when acetic acid is added to it.
The potassium salt may be :

A

K N O_{2}

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B

K_{2} S O_{3}

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C

K N O_{3}

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D

K B r

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Solution

The correct option is A $K N O_{2}$
Cobalt precipitates in sulphide form. When cobalt sulphide is treated with aqua regia and then with strong solution of potassium nitrite in the presence of acetic acid, a yellow precipitate of potassium hexanitritocobaltate (III) ( $K_{3} [C o (N O_{2})_{6}]$ ) complex is formed.
The reactions are as follows:
$C o S + H N O_{3} + 3 H C l \to C o C l_{2} + N O C l + S + 2 H_{2} O$
$C o C l_{2} + 7 K N O_{2} + 2 C H_{3} C O O H \to K_{3} [C o (N O_{2})_{6}] ↓ (yellow ppt.)$
$+ N O + H_{2} O + 2 K C l + 2 C H_{3} C O O K$

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Salt	Anion
A
B
C
D
E

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Q. The colour of the precipitate formed when Cobalt (

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) solution reacts with

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