The pH ammonium phosphate solution, if pk of phosphoric acid and pk of ammonium hydroxide are 5.23 a — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

**Step 1: Identify the salt type** Ammonium phosphate (NH₄H₂PO₄) is a salt of a weak acid (H₃PO₄) and weak base (NH₃), so it's acidic or basic depending on the relative strengths of the conjugate acid (NH₄⁺) and conjugate base (H₂PO₄⁻). **Step 2: Determine pKa and pKb values** - pKa of H₂PO₄⁻ (conjugate base of phosphoric acid) = 5.23 - pKb of NH₄⁺ (conjugate acid of ammonia) = 4.75 **Step 3: Apply the salt hydrolysis formula** For a salt of weak acid and weak base: $$pH = \frac{pK_w + pK_a + pK_b}{2}$$ Where pKw = 14 **Step 4: Substitute values** $$pH = \frac{14 + 5.23 + 4.75}{2}$$ $$pH = \frac{23.98}{2}$$ $$pH = 11.99$$ **Step 5: Recalculate using correct formula** $$pH = 7 + \frac{pK_a - pK_b}{2}$$ $$pH = 7 + \frac{5.23 - 4.75}{2}$$ $$pH = 7 + \frac{0.48}{2}$$ $$pH = 7 + 0.24 = 7.24$$ Therefore, the answer is 7.24.