Question

$C{r}_2{O}_7^{2-}\stackrel{pH=x}{\to }Cr{O}_4^{2-}\stackrel{pH=y}{\to }C{r}_2{O}_7^{2-}$.The `pH` values of x and y can be:

• A. 4 and 5
• B. 4 and 8
• C. 8 and 4
• D. 8 and 9

Answer 1

The correct option is C 8 and 4

In an alkaline medium, dichromate ions can be converted into chromate ions and in an acidic medium chromate ions can be converted to dichromate ions.

So the reaction will be,

$C{r}_2{O}_7^{2-}\stackrel{pH=8}{\to }Cr{O}_4^{2-}\stackrel{pH=4}{\to }C{r}_2{O}_7^{2-}$