Question

Write down the reaction involved in preparation of Potassium dichromate from chromine ore.

Answer 1

Following step reactions are involved in preparation of $K_{2}C{r}_2{O}_7$ from Chromite ore ($FeC{r}_2{O}_4$)

I. Formation of $N{a}_{2}Cr{O}_4$ (sodium chromate)

$4FeC{r}_2{O}_4+16NaOH+7O_2\to 8N{a}_{2}Cr{O}_4+2F{e}_2{O}_3+8H_{2}O$

II. Conversion of $N{a}_{2}Cr{O}_4$ to $N{a}_{2}C{r}_2{O}_7$

2$N{a}_{2}Cr{O}_4$ $+conc.H_{2}S{O}_4$ $\to$ $N{a}_{2}C{r}_2{O}_7$ + $N{a}_{2}S{O}_4$ $H_{2}O$

III. Conversion of $N{a}_{2}C{r}_2{O}_7$ to $K_{2}C{r}_2{O}_7$

$N{a}_{2}C{r}_2{O}_7$ +2KCl $\to$ $K_{2}C{r}_2{O}_7$ +2 NaCl.

Since the solubility of KCl is less than NaCl, so, $K_{2}C{r}_2{O}_7$ is obtained in form of orange crystals and the former can be removed by filtration.