Question

When $K_{2}C{r}_2{O}_7$ is treated with $H_2{O}_2$ then:

• A. in strong acidic medium deep blue-violet complex $CrO(O_2{)}_2$ is formed
• B. in less acidic medium violet, coloured complex $\left[CrO\right(O_2\left)\right(OH){]}^{-}$ is formed
• C. in alkaline medium $\left[Cr\right(O_2{)}_4{]}^{3-}$ is formed
• D. in ammonical solution $(N{H}_3{)}_{3}Cr{O}_4$ dark red-brown compound is formed.

Answer 1

Answer: (A), (B), (C), (D)

The correct options are
A in less acidic medium violet, coloured complex $\left[CrO\right(O_2\left)\right(OH){]}^{-}$ is formed
B in strong acidic medium deep blue-violet complex $CrO(O_2{)}_2$ is formed
C in alkaline medium $\left[Cr\right(O_2{)}_4{]}^{3-}$ is formed
D in ammonical solution $(N{H}_3{)}_{3}Cr{O}_4$ dark red-brown compound is formed.

$K_{2}C{r}_2{O}_7+4H_2{O}_2+H_{2}S{O}_4\to K_{2}S{O}_4+2CrO\left(O_2\right)+5H_{2}O$

deep blue - violet

The peroxide formed is decomposes rapidly in aqueous solution cno

into $C{r}^{3+}$ and oxygen. In less acidic solution the reaction gives a salt which is violet coloured and diamagnetic due to formation of $\left[CrO\right(O_2\left)\right(OH){]}^{-}$

In alkaline medium it gives a red - brown compound $K_{3}Cr{O}_8$

Where as in ammonical solution $(N{H}_4{)}_{3}Cr{O}_4$ is formed which is also a dark red - brown compound