Question

A list of reactions are given below.

(a) $Fe+2HCl\to FeC{l}_2+H_2$

(b) $FeS+2HCl\to FeC{l}_2+H_{2}S$

(c) $Fe+S\stackrel{\Delta }{\to }FeS$

(d) $NaCl+H_{2}S{O}_4\stackrel{<{200}^{o}C}{\to }NaHS{O}_4+HCl$

(e) $CuS{O}_4+H_{2}S\to CuS+H_{2}S{O}_4$

(f) $S+H_{2}S{O}_4\to 3S{O}_2+H_{2}O$

Identify redox reactions.

• A. a, c and f
• B. d and f
• C. c and d
• D. c, d and f

Answer 1

The correct option is A a, c and f

Redox reactions have both oxidation and reduction process. By calculating the oxidation states we can determine the redox system as:

a. $\stackrel{0}{Fe}+2\stackrel{+1}{H}\stackrel{-1}{Cl}\to \stackrel{+2}{Fe}\stackrel{-1}{C{l}_2}+\stackrel{0}{H_2}$

oxidation of $Fe$ and reduction of $H$

b. $\stackrel{+2}{Fe}\stackrel{-2}{S}+2\stackrel{+1}{H}\stackrel{-1}{Cl}\to \stackrel{+2}{Fe}\stackrel{-1}{{Cl}_2}+\stackrel{+1}{H_2}\stackrel{-2}{S}$

no oxidation or reduction

c. $\stackrel{0}{Fe}+\stackrel{0}{S}\stackrel{\Delta }{\to }\stackrel{+2}{Fe}\stackrel{-2}{S}$

oxidation of $Fe$ and reduction of $S$

d.$\stackrel{+1}{Na}\stackrel{-1}{Cl}+\stackrel{+1}{H_2}\stackrel{+6}{S}\stackrel{-2}{O_4}\stackrel{<200C}{\to }\stackrel{+1}{Na}\stackrel{+1}{H}\stackrel{+6}{S}\stackrel{-2}{O_4}+\stackrel{+1}{H}\stackrel{-1}{Cl}$

no oxidation or reduction

e. $\stackrel{+2}{Cu}\stackrel{+6}{S}\stackrel{-2}{O_4}+\stackrel{+1}{H_2}\stackrel{-2}{S}\to \stackrel{+2}{Cu}\stackrel{-2}{S}+\stackrel{+1}{H_2}\stackrel{+6}{S}\stackrel{-2}{O_4}$

no oxidation or reduction

f. $\stackrel{0}{S}+\stackrel{+1}{2H_2}\stackrel{+6}{S}\stackrel{-2}{O_4}\to 3\stackrel{+4}{S}\stackrel{-2}{O_2}+2\stackrel{+1}{H_2}\stackrel{-2}{O}$

oxidation and reduction of $S$

Therefore, reactions a, c and f are redox reactions. Option $A$ is correct.