Question

The following reaction is at equilibrium,
$F{e}_{\left(aq\right)}^{3+}+SC{N}_{\left(aq\right)}^{-}\rightleftharpoons \left[Fe\right(SCN{)}_{\left(aq\right)}^{2+};K_c=\frac{\left[Fe\right(SCN){]}^{2+}}{\left[F{e}^{3+}\right]\left[SC{N}^{-}\right]}$
In the above reaction, color 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 reacts with $SC{N}^{-}$ ions
• D. red colour intensity cannot be changed.

Answer 1

Answer: (A)

addition of KSCN

The given reaction is:-

${Fe}^{+}\left(aq\right)+{SCN}^{-}\left(aq\right)\rightleftharpoons {\left[Fe\left(SCN\right)\right]}^{2+}\left(aq\right)$

$K_C=\frac{{\left[Fe\left(SCN\right)\right]}^{2+}}{\left[{Fe}^{3+}\right]\left[{SCN}^{-}\right]}$

The red colour in the reaction appears due to formation of ${\left[Fe\left(SCN\right)\right]}^{2+}$ ion. So, as the reaction proceed more forwards formation of product, the intensity of red colour will increase, so, by applying Le Chaterlier's principle addition of $KSCN$ will facilitate such kind of colour change.