Question

An inorganic salt is a lemon yellow in color. It becomes orange in color like methyl orange when it is acidic and again becomes yellow when it is alkaline. The inorganic salt will be:
(a)- Copper nitrate
(b)- Ferric chloride
(c)- Potassium chromate
(d)- Potassium ferricyanide

Answer 1

Hint: The inorganic salts of potassium are mostly yellow or orange in color. Dichromate ion is formed when the chromate ion is acidified and chromate ion is formed when dichromate ion is alkalized.

Complete step by step answer:
So, in the question it is given that inorganic salt is lemon yellow in color, let us see all the options:
Copper nitrate is an inorganic salt that is blue crystalline solid having formula $Cu{{(N{{O}_{3}})}_{2}}$.
Ferric chloride is an inorganic salt that is black crystalline solid having formula $FeC{{l}_{3}}$.
Potassium chromate is an inorganic salt that is a lemon yellow solid powder having formula ${{K}_{2}}Cr{{O}_{4}}$.
Potassium ferricyanide is an inorganic salt that is a bright red solid having formula ${{K}_{3}}[Fe{{(CN)}_{6}}]$.
So, the chromate ion is lemon yellow in color.
The addition of acid to the chromate ion will form a dichromate ion and water molecule. When the dichromate ion is alkalized, chromate ion will be formed. The reaction is given below:
$2CrO_{4}^{2-}+2{{H}^{+}}\rightleftharpoons C{{r}_{2}}O_{7}^{2-}+{{H}_{2}}O$
The chromate ion is yellow and the dichromate ion is orange, this satisfies the second condition of the question.

So, the correct answer is an option (c)- Potassium chromate.

Note: For protecting the metals from corrosion and to improve paint adhesion chromates and dichromates are used in chrome plating. Chromates and dichromates of most of the elements are not very soluble in water.