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Preparations and Uses of Sodium Bicarbonate and Common Salt

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Question

For the purpose of systematic qualitative analysis, cations are classified into various groups on the basis of their behavior against some reagents. The group reagents used for the classification of most common cations are hydrochloric acid, hydrogen sulphide, ammonium hydroxide, and ammonium carbonate. Classification is based on whether a cation reacts with these reagents by the formation of precipitates or not.

An aqueous solution contains $H g^{2 +}$ , $H g_{2}^{2 +}$ , $P b^{2 +}$ and $C d^{2 +}$ . The addition of $2 M H C l$ will precipitate :

A

H g C l_{2}

only

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B

P b C l_{2}

only

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C

P b C l_{2}

and

H g_{2} C l_{2}

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D

P b C l_{2}

and

C d C l_{2}

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Solution

The correct option is C $P b C l_{2}$ and $H g_{2} C l_{2}$
Option (C) is correct.
The addition of $2 M H C l$ will precipitate $P b C l_{2}$ and $H g_{2} C l_{2}$ .
$2 M H C l$ is group reagent for group I cations. $P b C l_{2}$ and $H g_{2} C l_{2}$ will get precipitated, as their solubility products $(K_{s p})$ are less than that of other radical.

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For the purpose of systematic qualitative analysis, cations are classified into various groups on the basis of their behaviour against some reagents. The group reagents used for the classification of most common cations are hydrochloric acid. hydrogen sulphide, ammonium hydroxide, and ammonium carbonate.
Classification is based on whether a cation reacts with these reagents by the formation of precipitates or not.

Which one among the following pairs of ions can be separated by

H_{2} S

in presence of dilute hydrochloric acid?

Q. Assertion :Ammonium sulphide is used for testing 5th group cations. Reason: Most of the cations belonging to 5th group form different coloured precipitate with sulphides.

In qualitative analysis,

{I I I}^{r d}

F e^{3 +}, A l^{3 +}

C r^{3 +}

. The group reagent is ammonium hydroxide in the presence of ammonium chloride.

N H_{4} C I

is added to suppress the ionisation of

N H_{4} O H

so that only the

I I I^{r d}

group radicals are precipitated as their insoluble hydroxide and not the

I V^{t h}

V^{t h}

group radicals as the solubility products of their hydroxides are much higher. Before adding group reagent to the filtrate of IInd group, one drop of concentrated

H N O_{3}

(oxidising agent) is added and the content is boiled for 2-3 minutes and then cool because the solubility product of

F e (O H)_{2}

is very high as compared to

F e (O H)_{3}

. When a light bluish-green crystalline double salt-containing cations of III

^{r d}

group and zero groups are analysed. it responds to the following tests/reactions.
(a) Its aqueous solution gives a reddish-brown precipitate with an alkaline solution of potassium tetraiodomercurate (II)
(b) Its aqueous solution after boiling with conc.

H N O_{3}

gives a reddish-brown precipitate with sodium hydroxide.
(c) The solution of reddish-brown precipitate in oil.HCI gives blood red colouration with ammonium sulphocyanide and Prussian blue with potassium ferrocyanide.
(d) It's a very dilute solution gives a white precipitate with

(C H_{3} C O O)_{2} P b

solution and a white precipitate are only soluble in hot ammonium acetate.

Why one mL conc.

H N O_{3}

I I^{n d}

group filtrate before proceeding for

I I I^{r d}

group radicals?

Q. An aqueous solution containing

H g_{2}^{2 +}, H g^{2 +}, P b^{2 +}, F e^{2 +}

is treated with dil HCI. The cations that may be precipitate are __________.

Q. How many of the following cations belong to group IIA, III, IV, and V only in qualitative salt analysis?

S n^{2 +}, H g_{2}^{2 +}, P b^{2 +}, Z n^{2 +}, C u^{2 +}, C r^{3 +}, A s^{3 +}, M g^{2 +}, S b^{3 +}

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