Question

When \[{H_2}{O_2}\] is added to an acidified solution of \[{K_2}C{r_2}{O_7}\],the solution:
(A) Turns green due to the formation of \[C{r_2}{O_3}\]
(B) Turns yellow due to the formation of \[{K_2}Cr{O_4}\]
(C) Turns deep blue-violet due to the formation of \[CrO{({O_2})_2}\]
(D) Gives green precipitate due to the formation of \[Cr{(OH)_3}\]

Answer 1

Hint: In order to find what will be the product formed, when \[{H_2}{O_2}\] is added to \[{K_2}C{r_2}{O_7}\], we must have an idea about what are \[{K_2}C{r_2}{O_7}\] and \[{H_2}{O_2}\], what type of reaction is taking place. \[{K_2}C{r_2}{O_7}\] is the chemical formula for potassium dichromate and \[{H_2}{O_2}\]is the chemical formula for hydrogen peroxide.

Complete step by step answer:
Let us first understand about the potassium dichromate. Potassium dichromate is present as a red-orange crystal. It is odourless, non-combustible and highly corrosive in nature. Potassium dichromate will exist in solid state at room temperature. It is one of the most commonly used reagents in inorganic chemistry. It will act as a good oxidising agent for conducting various experiments.
When hydrogen peroxide is added to the acidified solution of potassium dichromate, we will obtain a deep blue-violet colour solution of chromium (VI) peroxide. The chemical formula for the chromium (VI) peroxide is \[CrO{({O_2})_2}\]. The reaction of the formation of deep blue-violet solution of chromium (VI) peroxide is given below:
\[4{H_2}{O_2} + 2{H^ + } + C{r_2}O_7^{2 - } \to 2CrO{({O_2})_2} + 5{H_2}O\]

Hence the correct answer is option (C).

Note:
Let us remember what are the different uses of potassium dichromate.
- Potassium dichromate is used in the leather tanning process and it is also used for producing potassium chrome alum.
- It is used as an oxidising agent in the photography industry and in screen printing photography.