Question

Which of the following is a redox reaction?

• A. $NaCl+KN{O}_3⟶NaN{O}_3+KCl$
• B. $Ca{C}_2{O}_4+2HCl⟶CaC{l}_2+H_2{C}_2{O}_4$
• C. $Ca(OH{)}_2+2N{H}_{4}Cl⟶CaC{l}_2+2N{H}_3$
• D. $2K\left[Ag(CN{)}_2\right]+Zn⟶2Ag$ $+K_2\left[Zn(CN{)}_4\right]$

Answer 1

Answer: (D)

(a) $\stackrel{+1}{\mathrm{Na}}\stackrel{-1}{\mathrm{Cl}}+\stackrel{+1}{K}\stackrel{-1}{N{O}_3}\to \stackrel{+1}{\mathrm{Na}}\stackrel{-1}{N{O}_3}+\stackrel{+1}{K}+\stackrel{-1}{\mathrm{Cl}}$

(b) $\stackrel{+2}{\mathrm{Ca}}{C}_2\stackrel{-2}{O_4}+2\stackrel{+1}{H}\stackrel{-1}{\mathrm{Cl}}\to \stackrel{+2}{\mathrm{Ca}}\stackrel{-1}{C{l}_2}+\stackrel{+1}{H_2}{C}_2\stackrel{-2}{O_4}$

(c)$\stackrel{+2}{\mathrm{Ca}}\stackrel{-1}{(OH{)}_2}+\stackrel{-3}{2N}\stackrel{+1}{H_4}\stackrel{-1}{\mathrm{Cl}}\to \stackrel{+2}{\mathrm{Ca}}\stackrel{-1}{C{l}_2}+\stackrel{-3}{2N}\stackrel{-1}{C{l}_2}+\stackrel{-3}{2N}\stackrel{+1}{H_3}+2\stackrel{+1}{H_2}\stackrel{-2}{O}$

in all these cases during reaction, there is no change in oxidation state of ion or molecule or constituent atom, these are simply ionic reactions.

(d) $2K\left[Ag(CN{)}_2\right]+Zn\to 2Ag+K_2\left[Zn(CN{)}_4\right]$

$A{g}^{+}\to$ Ag gaining of $e^{-},$ reduction $Zn\to Z{n}^{2+}$ loss of $e^{-}$, oxidation