Question

Potassium dichromate can be converted to potassium chromate by adding:
a.) KOH
b.) $Conc.{{H}_{2}}S{{O}_{4}}$
c.) $N{{H}_{4}}OH$
d.) $C{{H}_{3}}COOH$

Answer 1

Hint: We know that Potassium dichromate is ${{K}_{2}}C{{r}_{2}}{{O}_{7}}$ and potassium chromate is${{K}_{2}}Cr{{O}_{4}}$. When this conversion takes place then the colour of solution will change.

Complete step by step solution:
Potassium dichromate is a common inorganic chemical reagent. It is a crystalline ionic solid with a very bright, red-orange color. The salt is popular in the laboratory because it is not deliquescent in contrast to the more industrially relevant salt sodium dichromate.
Potassium dichromate is usually prepared by the reaction of potassium chloride on sodium dichromate. Alternatively, it can be also obtained from potassium chromate by roasting chromite ore with potassium hydroxide. It is soluble in water.
Potassium Chromate is a yellowish, crystalline, inorganic compound. It emits toxic chromium fumes upon heating. This substance is used in the manufacture of dyes and in textile dyeing processes.

Method of preparing potassium Chromate:
When an aqueous solution of Potassium dichromate is treated with calculated amount of KOH:

${{K}_{2}}C{{r}_{2}}{{O}_{7}}+2KOH\to 2{{K}_{2}}Cr{{O}_{4}}+{{H}_{2}}O$

The orange-red solution becomes yellow.

So, from the above explanation we can say that the option “A” is the correct option.

Alternative method:
An alkali is added to an orange red solution containing dichromate ion, a yellow solution is obtained due to the formation of chromate ions:

${{K}_{2}}C{{r}_{2}}{{O}_{7}}+{{K}_{2}}C{{O}_{3}}\to 2{{K}_{2}}Cr{{O}_{4}}+C{{O}_{2}}$

Note: Most commonly potassium dichromate used as an oxidizing agent in various laboratory and industrial applications. It is acutely and chronically harmful to health. Potassium chromate is highly corrosive and is a strong oxidizing agent.