Chapter 14, Problem 7RQ

Table 13-4 lists the stepwise K_a values for some polyprotic acids. What is the difference between a monoprotic acid, a diprotic acid, and a triprotic acid? Most polyprotic acids are weak acids; the major exception is H₂SO₄. To solve for the pH of a solution of H₂SO₄, you must generally solve a strong acid problem as well as a weak acid problem. Explain. Write out the reactions that refer to $K_{{\text{a}}_{\text{1}}}$ and $K_{{\text{a}}_{\text{2}}}$ for H₂SO₄.

For H₃PO₄, $K_{{\text{a}}_{\text{1}}}$ = 7.5 × 10⁻³, $K_{{\text{a}}_{\text{2}}}$ = 6.2 × 10⁻⁸, and $K_{{\text{a}}_{\text{3}}}$= 4.8 × 10⁻¹³. Write out the reactions that refer to the $K_{{\text{a}}_{\text{1}}}$, $K_{{\text{a}}_{\text{2}}}$and $K_{{\text{a}}_{\text{3}}}$equilibrium constants. What are the three acids in a solution of H₃PO₄? Which acid is strongest? What are the three conjugate bases in a solution of H₃PO₄? Which conjugate base is strongest? Summarize the strategy for calculating the pH of a polyprotic acid in water.