Calculate the exact pH of an aqueous solution of ammonium formate () at , assuming complete dissolution. Given that the dissociation constant for formic acid is exactly and the of ammonia is exactly .

Question

Calculate the exact pH of an aqueous solution of $1.0 	ext{ M }$ ammonium formate ($HCOONH_4$) at $25^\circ C$, assuming complete dissolution. Given that the dissociation constant $pK_a$ for formic acid is exactly $3.8$ and the $pK_b$ of ammonia is exactly $4.8$.

Prashant Kotian · Accepted Answer

Correct answer: 6.5. Ammonium formate is a salt derived from a weak acid () and a weak base (). The pH of its aqueous solution is given by the formula . The concentration term does not appear in this unapproximated formula. Substituting the known values: .

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