Question

Yellow coloured aqueous solution of sodium chromate changes to orange when acidified with sulphuric acid because:

• A. $H^{+}$ ions convert chromate ions to dichromate ions
• B. $H^{+}$ ions react with sodium chromate to give sodium ions which turn solution orange
• C. $C{r}^{+}$ ions are liberated in the solution which turn the solution orange
• D. sodium hydroxide is formed during the reaction which imparts orange colour to the solution

Answer 1

The correct option is A $H^{+}$ ions convert chromate ions to dichromate ions

The reaction between Sodium Chromate and Sulphuric acid is given as:

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

$Cr{O}_4^{2-}$ (chromate ion) is yellow in colour. When it is oxidized by H${}^{+}$ in $C{r}_2{O}_7^{2-}$ (dichromate ion), the colour changes to orange.