Question

Oxidation reaction involves loss of electrons, and reduction reaction involves gain of electrons. The reaction in which a species disproportionate into two oxidation states (lower and higher) is called disproportionate reaction
Which of the following statements is wrong?

• A. An acidified $K_{2}C{r}_2{O}_7$ paper on being exposed to $S{O}_2$ turns green
• B. Mercuric chloride and stannous chloride cannot exist as such
• C. Iron turning on addition to $CuS{O}_4$ solution decolourises the blue colour
• D. ${\left[Cu{l}_4\right]}^{2-}$ is formed but ${\left[CuC{l}_4\right]}^{2-}$ is not

Answer 1

Answer: (D)

a. $C{r}_2{O}_7^{2-}$ (orange red ) oxidises $S{O}_{2}toS{O}_4^{2-}$ and is itself reduced to $C{r}^{+3}$ (green)
$\underset{\text{(Orange)}}{C{r}_2{O}_7^{2-}}+3H^{\oplus }+3S{O}_2⟶\underset{\text{(Green)}}{2C{r}^{3+}}+3S{O}_4{}^{2-}+4H_{2}O$
b. Both reacts together
$\stackrel{+2}{HgC{l}_2}+\stackrel{+2}{SnC{l}_2}⟶\stackrel{+1}{⟶}\underset{\text{(White ppt)}}{H{g}_{2}C{l}_2\downarrow }+\stackrel{4}{\mathrm{Sn}}C{l}_4$
$\stackrel{+1}{H{g}_{2}C{l}_2}+\stackrel{+2}{SnC{l}_2}⟶\underset{\text{(Grey)}}{2Hg\downarrow }+\stackrel{+4}{SnC{l}_4}$
$\stackrel{0}{\mathrm{Fe}}+\underset{\text{(Blue)}}{\stackrel{+22}{CuS{O}_4}}⟶2$
d. ${\left[CuC{l}_4\right]}^{2-}$ is formed but ${\left[Cu{I}_4\right]}^{2-}$ is not
$I^{\ominus }$ ion reduces $C{u}^{2+}$ to $Cu{I}^{+1}$ and itself undergoes oxidation to form $I_2$. However, $C{l}^{\ominus }$ does not reduce $C{u}^{2+}$