Question

Write the equations involved in the preparation of potassium dichromate from sodium chromate ($N{a}_{2}Cr{O}_4$).

Answer 1

Sodium chromate is acidified with sulphuric acid to give a solution from which orange sodium dichromate, $N{a}_{2}C{r}_2{O}_7.2H_{2}O$ can be crystallised.
$2N{a}_{2}Cr{O}_4+2H^{+}\to N{a}_{2}C{r}_2{O}_7+2N{a}^{+}+H_{2}O$
Sodium dichromate is more soluble than potassium dichromate. The latter is therefore prepared by treating the solution of sodium dichromate with potassium chloride.
$N{a}_{2}C{r}_2{O}_7+2KCl\to K_{2}C{r}_2{O}_7+2NaCl$