Question

Which of the following mixtures is chromic acid?
(A) \[{K_2}C{r_2}{O_7}\] and conc. \[{H_2}S{O_4}\]
(B) \[{K_2}C{r_2}{O_7}\] and \[HCl\]
(C) \[{K_2}S{O_4}\] and conc. \[{H_2}S{O_4}\]
(D) \[{H_2}S{O_4}\] and \[HCl\]

Answer 1

Hint: Knowing the various chromic acid reactions and the compounds they produce is necessary to answer this issue. Concentrated sulfuric acid is mixed with a dichromate to create chromatic acid. As an oxidising agent, chromic acid is used to turn alcohol or aldehydes into carboxylic acid.

Complete Step by Step Solution:
Chromic acid is present as \[{H_2}Cr{O_4}\], as we are well aware. Chromium trioxide and water can also be combined to create it. When chromic acid is introduced to chromium trioxide, dichromic acid, which is present, is created.

While both chromic acid and sulphuric acid \[({H_2}S{O_4})\] are potent acids, only the first proton is easily lost in chromic acid \[({H_2}Cr{O_4})\].

The fully protonated form of the dichromate \[(C{r^2}{O_7}^-)\] ion is dichromic acid, or \[({H_2}C{r_2}{O_7})\]. It is also thought to be the result of mixing molecular chromic acid with chromium trioxide \[(Cr{O_3})\].

By combining the potassium dichromate and sulphuric acid, an acidified solution of chromic acid is created. Potassium sulphate and dichromic acid are produced. The following will happen as a result:
\[{K_2}C{r_2}{O_7}\; + \;\;{H_2}S{O_4} \to {K_2}S{O_4}\; + \;{H_2}C{r_2}{O_7}\]
Therefore, the correct option is: (A) \[{K_2}C{r_2}{O_7}\] and conc. \[{H_2}S{O_4}\].

Note: Chromic acid that has been acidified works well as an oxidizer in the experiment. But instead of decreasing itself, it produces a peroxide when it reacts with hydrogen peroxide. The dichromate ion will get protonated when acid is added to chromic acid or potassium dichromate.