Question

The following reaction is at equilibrium,
$\underset{\text{Yellow}}{F{e}_{(aq)}^{3+}}+\underset{\text{Colourless}}{SC{N}_{(aq)}^{-}}\rightleftharpoons \underset{\text{Deep red}}{[Fe(SCN){]}_{(aq)}^{2+}}$ ;
$K_c=\frac{{\left[Fe\left(SCN\right)\right]}^{2+}}{\left[F{e}^{3+}\right]\left[SC{N}^{-}\right]}$
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 $F{e}^{3+}$ ions
• C. addition of $H{g}^{2+}$ ions which react with $SC{N}^{-}$ 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 $H{g}^{2+}$ ions which remove $F{e}^{3+}$ or $SC{N}^{-}$ ions shift the equilibrium to the left and colour intensity decreases.