Chemistry - Salt Analysis Question with Solution | TestHub

Question Explanation :

Which product will form when ${\mathrm{CO}}_2$ gas passes through the solution of sodium chromate. Concept: "This question is based on confirmative test for chromium ion"

Solution:

1. CO₂ provides Acidity: CO₂ dissolves in water to form weak carbonic acid ($H_{2}C{O}_3$), which produces H⁺ ions, making the solution slightly acidic.

2. Equilibrium Shift: The yellow chromate ion ($Cr{O}_4^{2-}$ ) is in equilibrium with the orange dichromate ion ($C{r}_2{O}_7^{2-}$). Increased H⁺ shifts the equilibrium to the right.

$$2Cr{O}_4^{2-}(yellow)+2H^{+}\rightleftharpoons C{r}_2{O}_7^{2-}(orange)+H_{2}O$$

3. Conclusion: The yellow solution of sodium chromate changes to an orange solution of sodium dichromate ($N{a}_{2}C{r}_2{O}_7$). The chromium oxidation state remains +6.

Final Answer: Option (B)