She flipped to the data sheet. Ka1 of H₂SO₃ = 1.54 × 10⁻². Ka2 = 1.02 × 10⁻⁷. Kb for HSO₃⁻ = Kw/Ka1 = (1×10⁻¹⁴)/(1.54×10⁻²) = 6.49×10⁻¹³.
She wrote: At equivalence point for first proton: species present = HSO₃⁻. This hydrolyses in water. Two equilibria: HSO₃⁻ + H₂O ⇌ H₂SO₃ + OH⁻ (Kb1) AND HSO₃⁻ ⇌ H⁺ + SO₃²⁻ (Ka2). Since Ka2 > Kb1, solution is acidic? No—check values. hsc chemistry 9 crack
Compare Ka2 (1.02×10⁻⁷) to Kb (6.49×10⁻¹³). Ka2 is much larger . So the HSO₃⁻ acts as a weak acid. The solution is slightly acidic. Of course. The pH at equivalence is below 7. Not neutral. That was the trap. She flipped to the data sheet
"You can't just will the answer," she whispered. That was her problem. She had spent the whole year trying to memorise chemistry like it was history. Dates. Formulas. But chemistry wasn't a list. It was a story. Protons moving. Electrons trading places. Water molecules huddling around ions like concerned neighbours. Kb for HSO₃⁻ = Kw/Ka1 = (1×10⁻¹⁴)/(1