Question

Assertion:
In a procedural modification of the cobalt nitrate test, $2 - 3$ drops of nitric acid and $2 - 3$ drops of cobalt nitrate solution are added to the residue of the charcoal cavity. A thin strip of filter paper is dipped in the solution and burned in a non-luminous part of the flame. Different cations give ash characteristic colors.
Reason:
The Ash test is done in a similar way.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect

Answer 1

This problem is based on the qualitative analysis of cations. This test is the preliminary test for cations. Cations in a mixture of a cation and an anion can be separated. Also, anions can also be determined using several tests.

Complete step by step answer:
Qualitative analysis of cations uses precipitation as a method to separate them from a particular mixture. The preliminary tests involve the following tests:
- Physical appearance
- Charcoal cavity test
- Borax bead test
- Flame test
Charcoal cavity test is been stated in this question. In this test, initially, the cations are converted to their carbonate Formby reacting with sodium carbonate.
E.g. ${{ZnS}}{{{O}}_4} + {{N}}{{{a}}_2}{{C}}{{{O}}_3} \to {{ZnC}}{{{O}}_3} + {{N}}{{{a}}_2}{{S}}{{{O}}_4}$
This happens in a charcoal cavity. Here, it decomposes into the form of its oxides. Now this residue in the charcoal cavity undergoes a cobalt nitrate test. It is done only when the color of the residue is white. It is added with $2 - 3$ drops of cobalt nitrate solution. Then it is burnt in a non-luminous flame and we have to note the color of residue. Cobalt oxide, which is formed by the decomposition of cobalt nitrate on heating, reacts with the oxide of cation to give the color.
i.e. ${{CoO}} + {{ZnO}} \to {{CoO}}.{{ZnO}}$

But ash test is a different process. It is done by burning a polymer at a very high temperature, i.e. ${500^ \circ }{{C}}$ and after cooling the crucible is weighed to measure the amount of ash residue.
So only Assertion is correct. The correct answer is option “C” .

Additional Information : The cations which show white color of residue in the charcoal cavity are ${{B}}{{{a}}^{2 + }},{{C}}{{{a}}^{2 + }},{{M}}{{{g}}^{2 + }},{{Z}}{{{n}}^{2 + }},{{A}}{{{l}}^{3 + }}$. So only these cations undergo cobalt nitrate test.

Note: Charcoal cavity is done using a charcoal block. The charcoal block is heated to make a small cavity in it. Now the mixture of cation and anion is mixed with the carbonate and a drop of water is added to it. Now it is heated using reducing flame. Detection of cations is done using the color of residue which is remained in the charcoal cavity or deposit that is outside the cavity.