Question

The following reaction is at equilibrium,
$\underset{\text{Yellow}}{Fe^{3+}_{(aq)}}+ \underset{\text{Colourless}}{SCN^{-}_{(aq)}} \rightleftharpoons \underset{\text{Deep red}}{[Fe(SCN)]^{2+}_{(aq)}}$ ;
$K_{c}=\frac{\left[Fe\left(SCN\right)\right]^{2+}}{\left[Fe^{3+}\right]\left[SCN^{-}\right]}$
In the above reaction, colour intensity of red colour can be increased by

• A. addition of $KSCN$
• B. addition of oxalic acid which reacts with $Fe^{3+}$ ions
• C. addition of $Hg^{2+}$ ions which react with $SCN^-$ ions
• D. red colour intensity cannot be changed

Answer 1

Answer: (A)

Addition of $KSCN$ increases the colour intensity of the solution as it shifts the equilibrium to right. Addition of reagents like oxalic acid or $Hg^{2+}$ ions which remove $Fe^{3+}$ or $SCN^-$ ions shift the equilibrium to the left and colour intensity decreases.