Question

Identify the reactions in which dichromate acts as an oxidising reagent.
I. $C{r}_2{O}_7^{2-}+6F{e}^{2+}+14H^{+}⟶2C{r}^{3+}+6F{e}^{3+}+7H_{2}O$
II. $C{r}_2{O}_7^{2-}+2O{H}^{-}⟶2Cr{O}_4^{2-}+H_{2}O$
III. $C{r}_2{O}_7^{2-}+6I^{-}+14H^{+}⟶2C{r}^{3+}+3I_2+7H_{2}O$
IV. $N{a}_{2}C{r}_2{O}_7+2KCl⟶K_{2}C{r}_2{O}_7+2NaCl$

• A. I, IV
• B. I,II
• C. II, III
• D. II, IV

Answer 1

Answer: (B)

In reaction I and III, dichromate acts as an oxidising reagent.

(I) $C{r}_2{O}_7^{2-}+6F{e}^{2+}+14H^{+}⟶2C{r}^{3+}+6F{e}^{3+}+7H_{2}O$

In the above reaction, $C{r}^{6+}$ reduced to $C{r}^{3+}$ and $F{e}^{2+}$ oxidised to $F{e}^{3+}$

(II) $C{r}_2{O}_7^{2-}+2O{H}^{-}⟶2Cr{O}_4^{2-}+H_{2}O$

In the above reaction, there is no change occuring in the oxidation state of $Cr$.

(III) $C{r}_2{O}_7^{2-}+6I^{-}+14H^{+}⟶2C{r}^{3+}+3I_2+7H_{2}O$

In the above reaction, $C{r}^{6+}$ has reduced to $C{r}^{3+}$ and $I^{-}$ has oxidised to $I_2$.

(IV) $N{a}_{2}C{r}_2{O}_7+2KCl⟶K_{2}C{r}_2{O}_7+2NaCl$

In the above reaction, no change in the oxidation state of $Cr$ has taken place.