Question

If ${CO}_2$ is passed into waste water containing $Cr{O}_4^{2-}$ (yellow) then:

• A. solution turn green due to formation of ${Cr}^{3+}$
• B. solution turns blue due to formation of $Cr{O}_5$
• C. solution turns orange due to formation of ${Cr}_2{O}_7^{2-}$
• D. no effect takes place

Answer 1

Answer: (C)

solution turns orange due to formation of ${Cr}_2{O}_7^{2-}$

First $C{O}_2$ reacts with water and forms unstable acid, which further gives hydrogen ion in solution.

$C{O}_2+H_{2}O\rightleftharpoons H_{2}C{O}_3\rightleftharpoons 2H^{+}$

Now, this ion reacts with $Cr{O}_4^{2-}$ and forms orange ${Cr}_2{O}_7^{2-}$ solution.

$\underset{yellow}{2Cr{O}_4^{2-}}+2H^{+}⟶H_{2}O+\underset{orange}{{Cr}_2{O}_7^{2-}}$