Question

Which is called chromic acid?
A. CrO
B. $C{r}_2{O}_3$
C. $Cr{O}_3$
D. $Cr{O}_2$

Answer 1

Hint: Chromic acid can also be known as Tetraoxo Chromic acid. It is a dark solid which is purple in colour. It is bright orange when wet and it dissolves in water with hydrolysis. It can be used as an oxidising agent.

Complete step by step answer:
- $Cr{O}_3$ is the acidic anhydride of chromic acid.
- It can be made by pouring concentrated sulphuric acid into a dichromate, which contains many different compounds like solid chromium trioxide.
- Chromic acid is first diluted in lots of water. And after dilution, it can be neutralised with a reducing agent.
- Chromic acid is having a wide range of applications. Some of them are:
- Chromic acid is actually an intermediate in chromium plating, it is used in coloured glasses and in ceramic glazes.
- It is also found that a solution of chromic acid and sulphuric acid is a powerful oxidising agent, and can be also used to clean various laboratory glassware.
- The dilute solutions of chromic acid are used to oxidise secondary or primary alcohols to aldehydes and ketones. It is also used for qualitative analytical tests for the presence of primary or secondary alcohols.
- Hence, we can say that the correct option is (C) that is $Cr{O}_3$ called as chromic acid.
So, the correct answer is “Option C”.

Note: - It is found that chromic oxides are toxic and carcinogenic. Due to this oxidation of chromic acid is not used on industrial scale.
- We can see that Chromic acid is able to identify aldehydes, secondary alcohol and primary alcohol, except tertiary alcohols, as these do not react with chromic acid under mild conditions