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Laboratory Method

Identify the ...

Question

Identify the inorganic salt $A$ whose aqueous solution gives following reactions.
(i) pale yellow precipitate with $A g N O_{3}$ solution, insoluble in dil $H N O_{3}$
(ii) white precipitate with $N H_{4} O H$ and also with $N a O H$ solution. However the precipitate does not dissolve in excess of $N H_{4} O H$ but soluble in excess of $N a O H$ .

A l B r_{3}

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A l C l_{3}

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N a B r

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N a I

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Solution

The correct option is A $A l B r_{3}$
(i) This is the Silver nitrate test for halide ions, done in aqueous solution. The solution is acidified by adding dilute nitric acid. The nitric acid reacts with, and removes, other ions that might also form precipitates with silver nitrate. Silver nitrate solution is then added, and the halide can be identified from the colour of the precipitate formed: Fluoride ion - no precipitate, Chloride ion - gives white precipitate, Bromide ion - gives pale yellow precipitate, Iodide ion - gives yellow precipitate. Except Fluoride ion, all others are insoluble in dil Nitric acid. Thus, A contains Bromide ion. So the options could be either (A) $A l B r_{3}$ or (C) NaBr
(ii) On treatment with Sodium hydroxide or Ammonium hydroxide solution a white precipitate was formed. This suggests presence of Aluminium ion in contrast to Sodium ion, as Aluminium hydroxide formed by the two reactions give a white precipitate. Also, Aluminium hydroxide is soluble in strong base sodium hydroxide, while it is insoluble in weak base ammonium hydroxide. Thus, A contains Aluminium ion. Hence the right answer is option (A) $A l B r_{3}$ .
Reactions in the image below futher explain (i) and (ii):

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Similar questions

Q. The aqueous solution of an inorganic compound (X) gives white precipitate with

N H_{4} O H

which does not dissolve in excess of

N H_{4} O H

This aqueous solution also gives white precipitate with

A g N O_{3}

and the precipitate is soluble in dilute

H N O_{3}

. Here, (X) is :

Q. Identify the cations in each of the following cases :
(i)

N a O H

solution when added to the Solution (A) gives a reddish brown precipitate.
(ii)

N H_{4} O H

Solution when added to the Solution (B) gives white precipitate which does not dissolve in excess.
(iii)

N a O H

Solution when added to Solution (C) gives white precipitate which is insoluble in excess.

Q. (A), a colourless solution, gives white precipitate (B) with NaOH solution but the precipitate dissolves in excess of NaOH forming (C). (C) does not give any precipitate with

H_{2} S

but on boiling with

N H_{4} C l

, white precipitate (B) appears. (A) also gives yellow precipitate with

A g N O_{3}

. (A), (B) and (C) are as follows:

(A) :

A l B r_{3}

(B) :

A l (O H)_{3}

and (C) :

N a A l O_{2}

If true enter 1, if false enter 0.

Q. An inorganic compound

A

shows the following reaction:
(i) It is white solid, exists as dimer and fumes in the wet air.
(ii)It sublimes at

180^{\circ} C

and forms monomer if heated to

400^{\circ} C

.
(iii) Its aqueous solution turns blue litmus to red and gives a white precipitate with

A g N O_{3}

solution, which is soluble in

N H_{4} O H

.
Addition of

N H_{4} O H

and NaOH separately to the solution of

A

gives a gelatinous precipitate which in however soluble in excess of

N a O H

.
The compound

A

is:

Q. The aqueous solution of inorganic compound

(X)

yielded a white precipitate when treated with dilute

H N O_{3}

and

A g N O_{3}

. Another sample of the solution of

(X)

when treated with

N a O H

gave a white precipitate first which dissolved in excess of

N a O H

yielding a colorless solution. When

H_{2} S

gas was passed through that solution a white precipitate was obtained.

Identify the compound

(X)

and give the reactions.

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