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31.
An aqueous solution of a salt $$X$$ turns blood red on treatment with $$CN{S^ - }$$ and blue on treatment with $${K_4}\left[ {Fe{{\left( {CN} \right)}_6}} \right].X$$ also gives a positive chromyl chloride test. The salt $$X$$ is :
32.
An aqueous solution of a substance gives a white precipitate on treatment with $$dil.\,HCl$$ which dissolves on heating. When $${H_2}S$$ is passed through the hot acidic solution, a black precipitate is obtained. The substance is a
A
$$Hg_2^{2 + }$$ salt
B
$$C{u^{2 + }}$$ salt
C
$$A{g^ + }$$ salt
D
$$P{b^{2 + }}$$ salt
Answer :
$$P{b^{2 + }}$$ salt
$$PbC{l_2}$$ is insoluble in cold water, soluble in hot water and $$PbS$$ is black ppt in acidic medium.
33.
A salt on treatment with $$dil.HCl$$ gives a pungent smelling gas and a yellow precipitate. The salt gives green flame when tested. The solution gives a yellow precipitate with potassium chromate. The salt is
A
$$NiS{O_4}$$
B
$$Ba{S_2}{O_3}$$
C
$$Pb{S_2}{O_3}$$
D
$$CuS{O_4}$$
Answer :
$$Ba{S_2}{O_3}$$
Gas evolved is $$S{O_2}$$
34.
The equation which is balanced and represents the correct product(s) is:
35.
$$\left[ X \right] + {H_2}S{O_4} \to \left[ Y \right]$$ colourless gas with irritating smell, $$\left[ Y \right] + {K_2}C{r_2}{O_7} + {H_2}S{O_4} \to $$ green solution. $$\left[ X \right]$$ and $$\left[ Y \right]$$ are :
A
$${\text{SO}}_3^{2 - },S{O_2}$$
B
$$C{l^ - },HCl$$
C
$${S^{2 - }},{H_2}S$$
D
$$CO_3^{2 - },C{O_2}$$
Answer :
$${\text{SO}}_3^{2 - },S{O_2}$$
$$S{O_2}\,{\text{and}}\,{H_2}S,$$ both being reducing agents, can turn acidified dichromate solution green. $$S{O_2}$$ can be obtained by the action of acid upon sulphite, while $${H_2}S$$ is evolved by the action of acid upon sulphide. However, $$S{O_2}$$ has a burning sulphur smell which is irritating. $${H_2}S$$ has rotten egg like smell.
36.
The ion that cannot be precipitated by both $$HCl\,{\text{and}}\,{H_2}S$$ is
A
$$P{b^{2 + }}$$
B
$$C{u^ + }$$
C
$$A{g^ + }$$
D
$$S{n^{2 + }}$$
Answer :
$$S{n^{2 + }}$$
$$S{n^{2 + }}{\text{can be precipitated by }}{H_2}S{\text{ but not by }}HCl.{\text{ }}$$
37.
A solution containing $$A{s^{3 + }},C{d^{2 + }},N{i^{2 + }}$$ and $$Z{n^{2 + }}$$ is made alkaline with dilute $$N{H_4}OH$$ and treated with $${H_2}S.$$ The precipitate obtained will consist of
A
$$A{s_2}{S_3}\,{\text{and}}\,CdS$$
B
$$CdS,NiS\,{\text{and}}\,ZnS$$
C
$$NiS\,{\text{and}}\,ZnS$$
D
$${\text{Sulphide of all }}ions$$
Answer :
$${\text{Sulphide of all }}ions$$
$$A{s^{3 + }}$$ and $$C{d^{2 + }}$$ are the radicals of group $$II,$$ whereas $$N{i^{2 + }}\,\& \,Z{n^{2 + }}$$ are the radicals of group $$IV.$$ The solubility product of group $$IV$$ radicals is higher as compared to group $$II.$$ $$N{H_4}OH$$ increases the ionisation of $${H_2}S$$ by removing $${H^ + }$$ of $${H_2}S$$ as unionisable water.
$${H_2}S \rightleftharpoons 2{H^ + } + {S^{2 - }};{H^ + } + O{H^ - } \to {H_2}O$$
Thus excess of sulphide ions are present which leads to the precipitation of all the
four ions.
Note : $$HCl$$ decreases ionisation of $${H_2}S$$ whereas $$N{H_4}OH$$ increases the ionisation of $${H_2}S.$$
38.
An aqueous solution of $$FeS{O_4},A{l_2}{\left( {S{O_4}} \right)_3}$$ and chrome alum is heated with excess of $$N{a_2}{O_2}$$ and filtered. The materials obtained are :-
A
A colourless filtrate and a green residue.
B
A yellow filtrate and a green residue.
C
A yellow filtrate and a brown residue.
D
A green filtrate and a brown residue.
Answer :
A yellow filtrate and a green residue.
Green residue is due to $$Fe{\left( {OH} \right)_2}$$ and yellow filtrate is due to chromate $$ions\,CrO_4^{2 - }$$
39.
When $${H_2}S$$ is passed through $$H{g_2}S$$ we get
A
$$HgS$$
B
$$HgS + H{g_2}S$$
C
$$H{g_2}S + Hg$$
D
$${\text{None of these}}$$
Answer :
$$H{g_2}S + Hg$$
When $${H_2}S$$ is passed through $$H{g_2}S$$ we get a mixture of mercurous sulphide and mercury $$\left( {H{g_2}S + Hg} \right).$$
40.
Which of the statements is not true ?
A
On passing $${H_2}S$$ through acidified $${K_2}C{r_2}{O_7}$$ solution, a milky colour is observed
B
$$N{a_2}C{r_2}{O_7}$$ is preferred over $${K_2}C{r_2}{O_7}$$ in volumetric analysis
C
$${K_2}C{r_2}{O_7}$$ solution in acidic medium is orange
D
$${K_2}C{r_2}{O_7}$$ solution becomes yellow on increasing the $$pH$$ beyond 7
Answer :
$$N{a_2}C{r_2}{O_7}$$ is preferred over $${K_2}C{r_2}{O_7}$$ in volumetric analysis
Being hygroscopic, sodium dichromate, $$N{a_2}C{r_2}{O_7}$$ cannot be used in volumetric analysis. All other given statements are true.