Question

When potassium cyanide reacts with water, will the resulting solution be acidic, alkaline or neutral? Justify your answer.

Answer 1

Hint: The reaction of potassium cyanide in water is a violent reaction that undergoes anionic hydrolysis to form a strong electrolyte that is alkaline in nature. The overall reaction is an equilibrium favoured process.

Complete step by step answer:
The reaction of water with potassium cyanide, KCN, produces potassium hydroxide which is alkaline in nature. The equilibrium reaction between KCN and water can be represented as below:
  ${\text{KCN + }}{{\text{H}}_{\text{2}}}{\text{O}} \rightleftarrows {{\text{K}}^{\text{ + }}}{\text{ + C}}{{\text{N}}^{\text{ - }}}{\text{ + }}{{\text{H}}^{\text{ + }}}{\text{ + O}}{{\text{H}}^{\text{ - }}} \\
  {{\text{H}}^{\text{ + }}}{\text{ + C}}{{\text{N}}^{\text{ - }}} \rightleftarrows {\text{HCN}} \\
  {{\text{K}}^{\text{ + }}}{\text{ + O}}{{\text{H}}^{\text{ - }}} \rightleftarrows {\text{KOH}} \\ $
Hydrogen cyanide, HCN is a weak acid thus dissociates to give less ${{\text{H}}^{\text{ + }}}$ whereas the potassium hydroxide, KOH formed dissociates completely since it is a strong electrolyte. The dissociation of HCN is an anionic hydrolysis. The nature of KOH is a strong base which is alkaline in nature. In other words, the dissociation of KCN produces ${\text{C}}{{\text{N}}^{\text{ - }}}$ which abstracts the proton from the water to form HCN thus the left out ${\text{O}}{{\text{H}}^{\text{ - }}}$ ions combines with $ {{\text{K}}^{\text{ + }}} $ ions to form KOH.
Potassium cyanide is a salt of strong base and weak acid. The compound is water reactive which produces a strong base that reacts violently and corrosive in nature. Anionic hydrolysis of KCN produces strong base KOH. The potassium cyanide is bitter in taste which is quite explosive. Handling of such chemicals must be done with precaution.
Hence, when potassium cyanide reacts with water, the resulting solution will be alkaline.

Note:
The potassium cyanide in water solution is basic in nature. Besides, the pH of the resulting solution also increases. This also depicts the basic nature of the resulting solution.