Question

When hydrogen peroxide is added to acidified potassium dichromate, a blue colour is produced due to formation of?

• A. $Cr{O}_3$
• B. $C{r}_2{O}_3$
• C. $Cr{O}_5$
• D. $Cr{O}_4^{2-}$
• E. $C{r}_2{O}_7^{2-}$

Answer 1

The correct option is C $Cr{O}_5$

Step (i) $K_{2}C{r}_2{O}_7+H_{2}S{O}_4\to K_{2}S{O}_4+H_{2}C{r}_2{O}_7$

Step (ii ) $[H_2{O}_2\to H_{2}O+(O\left)\right]4$

Step (iii) $H_{2}C{r}_2{O}_7+4\left(O\right)\to 2Cr{O}_5+H_{2}O$
Hence, $K_{2}C{r}_2{O}_7+H_{2}S{O}_4+4H_2{O}_2\to 2Cr{O}_5+K_{2}S{O}_4+5H_{2}O$

The formation of Chromium Pentaoxide leads to the formation of blue colour from orange (as potassium dichromate is orange in colour). Chromium Pentaoxide is blue, so we get a blue colour after the reaction.

In the reaction, Hydrogen peroxide acts as an oxidizing agent, because it gets reduced, and its oxidation number changes to -2 from -1

Hence, the correct option is $C$