Calculate the pH of a 0.437 M aqueous solution of hydrocyanic acid (HCN, Ka = 4.0×10-10) and the equilibrium concentrations of the weak acid and its conjugate base.

pH=4.88

Explanation:

Hello,

In this case, the undergoing dissociation reaction is:

In such a way, the law of mass action becomes:

Which in terms of the change due to the reaction extent, goes:

Thus, solving for by either quadratic equation or solver, the results are:

Clearly, the answer is:

In this manner, since equals the concentration of hydrogen ions, the pH turns out:

And the concentration of the HCN and the CN⁻:

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