Is KCN acidic, basic, or neutral (dissolved in water)?

To tell if KCN (Potassium cyanide) forms an acidic, basic (alkaline), or neutral solution we can use these three simple rules along with the neutralization reaction that formed KCN .

First we need to figure out the acid and base that were neutralized to form Potassium cyanide. The equation for KCN is:

HCN + KOH = KCN + H2O
It is also useful to have memorized the common strong acids and bases to determine whether KCN acts as an acid or base in water (or if it forms a neutral solution).

Strong acids: HCl, H2SO4, HNO3, HBr, HI, HClO4
Weak acids: HF, CH3COOH, H2CO3, H3PO4, HNO2, H2SO3
Strong Bases: LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
Weak Bases: NH3, NH4OH

Note that we are talking about whether KCN is an acid, base, or neutral when dissolved in water.

Salts of strong bases and strong acids: pH will remain neutral at 7.
Salts of weak bases and strong acids: pH less than 7 (acidic).
Salts from strong bases and weak acids: pH greater than 7 (alkaline).

Based on these rules, the solution of KCN dissolved in water is basic.

For polyprotic acids (e.g. H3PO4) it’s a bit more complicated and we need to use Ka and Kb to determine the pH of the resulting solution.

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