Question

Which of the following statement(s) is/are correct ?

• A. $K_{2}C{r}_2{O}_7$ solution becomes yellow on increasing pH beyond $7$
• B. Orange colour of $C{r}_2{O}_7^{2–}$ is due to d-d transition
• C. $N{a}_{2}C{r}_2{O}_7$ is preferred over $K_{2}C{r}_2{O}_7$ in volumetric analysis
• D. Both (B) & (C)

Answer 1

The correct option is A $K_{2}C{r}_2{O}_7$ solution becomes yellow on increasing pH beyond $7$

(A) Organe colour of $C{r}_2{O}_7^{2–}$ is due to charge tranfer spectra.
(B) Because of hygroscopic nature of $N{a}_{2}C{r}_2{O}_7$, it is difficult to prepare its standard solution for volumetric analysis. Hence $K_{2}C{r}_2{O}_7$ is preffered over $N{a}_{2}C{r}_2{O}_7$ in volumetric analysis due to its non hygroscopic nature
(C) On acidifying chromates, $Cr{O}_4^{2-}$ form $HCr{O}_4^{-}$ and orange red dichromates $C{r}_2{O}_7^{2-}$.
So on addition of bases on dichromate solution or increasing pH of the dichromate solution it will become yellow due to the formation of chromates.