Question

A colorless solid X produces black spots on the skin. Aqueous solution of X gives brown ring test and gives a yellow precipitate with potassium iodide solution. The compound X is _ _ _ .
(A) Iron (II) nitrate
(B) Zinc nitrate
(C) Silver nitrate
(D) sodium nitrate

Answer 1

Hint: A variety of analytic methods that can qualitatively or quantitatively determine the inorganic elemental composition of solids include cations, or anions, or metals, or inorganic salts by inorganic analysis. Inorganic testing and techniques to identify and measure inorganic elements within solid and liquid samples have been provided in inorganic analysis.

Complete answer:
The detection or identification of individual elements or ions entering into the chemical composition of a substance is the main objective of the qualitative analysis.
The branch of analytical chemistry which deals with the identification of the number of constituents present in the given unknown sample is known as qualitative analysis.
Principle of qualitative analysis:
An analytical technique concerned with the identification of positive ion (cation) and negative ion (anion) part of single salt or mixture of two or more simple salts in qualitative analysis.
Let us find the compound X, which gives a yellow precipitate with a potassium iodide solution.
(i) Iron (II) nitrate - $Fe{{(N{{O}_{3}})}_{2}}$ reaction with KI is a double displacement reaction.
$KI+Fe{{(N{{O}_{3}})}_{2}}\to Fe{{I}_{2}}+KN{{O}_{3}}$
(ii) Zinc nitrate - $Zn{{(N{{O}_{3}})}_{2}}$ reaction with KI produces potassium nitrate and zinc iodide
$Zn{{(N{{O}_{3}})}_{2}}+2KI\to 2KN{{O}_{3}}+Zn{{I}_{2}}$
(iii) Silver nitrate - $AgN{{O}_{3}}$ aqueous solution reaction with KI gives a yellow precipitate of silver iodide will form.
$AgN{{O}_{3}}(aq)+KI(aq)\to KN{{O}_{3}}(aq)+AgI(s)\downarrow $
(iv) Sodium nitrate - $NaN{{O}_{3}}$reaction with KI produces potassium nitrate and sodium iodide
$NaN{{O}_{3}}+KI\to KN{{O}_{3}}+NaI$
Among all the above reactions, $AgN{{O}_{3}}$ aqueous solution reaction with KI gives a yellow precipitate of silver iodide and silver nitrate is a colorless solid which produces black spots on the skin.
Hence, compound X is silver nitrate.

The correct answer is option C.

Note:
Physicochemical and chemical, physical methods are used for qualitative analysis. The element or ion which is to be identified is converted to new compounds having some characteristics properties based on color, odor, and any chemical observation by chemical methods.