Question

The chromate ion in acidic medium changes to __________

• A. $Cr{O}_4^{2-}$
• B. $C{r}_3{O}_{10}^{2-}$
• C. $C{r}_2{O}_7^{2-}$
• D. none of these

Answer 1

The correct option is C $C{r}_2{O}_7^{2-}$

The chromate ion (yellow colour) in acidic medium changes to dichromate ion $C{r}_2{O}_7^{2-}$(orange colour). In alkaline medium, reverse happens.
In solution, the dichromate ions convert to chromate ions by the action of a base. Thus chromate ion and dichromate ion exists in equilibrium.
$2Cr{O}_4^{2-}\left(aq\right)+2H^{+}\left(aq\right)\to C{r}_2{O}_7^{2-}\left(aq\right)+H_{2}O\left(l\right)$
(yellow) (orange)