Question

When solid potassium cyanide is added in water then :
(A)- pH will decrease
(B)- electrical conductivity will not change
(C)- pH will increase
(D)- pH will remain the same

Answer 1

Hint: Potassium cyanide is a chemical compound with chemical formula KCN. Potassium cyanide is colorless, crystalline salt which is highly soluble in water.

Complete answer:
-Potassium cyanide is highly soluble in water will readily dissociate to into potassium and cyanide ions by the following reaction-
$KCN(s)\to {{K}^{+}}(aq)+C{{N}^{-}}(aq)$

-Potassium cations will not hydrolyze in water, but cyanide anions will attract the protons from the water and will give the following reaction-
$C{{N}^{-}}(aq)+{{H}_{2}}O(l)\rightleftharpoons HCN(aq)+O{{H}^{-}}(aq)$

-Since the above reaction is generating hydroxide ions, it will increase the pH of the solution making it basic.

So, the correct answer is pH will increase, i.e option C.

Additional information:
-Potassium cyanide is a very toxic chemical.
-Most of the potassium cyanide is used in gold mining, organic synthesis, and electroplating. However, they have smaller applications in custom jewelry for chemical gilding and buffing.
-Nearly 50,000 tons of potassium cyanide is produced yearly by treating hydrogen cyanide with an aqueous solution of potassium hydroxide, followed by evaporation of the solution in a vacuum.
$HCN+KOH\to KCN+{{H}_{2}}O$
-Potassium cyanide and sodium cyanide are used in the organic synthesis for the preparation of nitriles and carboxylic acids, particularly by Von Richter's reaction. It is also useful for the synthesis of hydantoins which are useful synthetic intermediates.
-Potassium cyanide is also used as a photographic fixer in the wet plate collodion process.

Note:
Potassium cyanide in its moist crystalline solid-state emits small amounts of hydrogen cyanide due to the hydrolysis which smells like bitter almost. The ability to smell this is a genetic trait and not everyone can do so. It is also a potent inhibitor of cellular respiration.