5. What is the pH of an ammonium acetate solution? The pKa of the ammonium (NH4+) cation is 9.3. Always bear in mind that the pKa refers to the ability of the proton donor form to release the proton into water to form H3O+. Since this is the salt of a weak acid (NH4+) and the conjugate base of a weak acid (acetate anion), the following equation is used. Note that molar concentration is not a variable in this calculation.
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