Question

Tartaric acid, C4H6O6, has the first ionization constant with the value: Ka1 = 9.20 × 10-4. Calculate the value of pKb for the conjugate base of tartaric acid. 10.963 3.036 1.087 x 10-11 9.20 x 10-4

Answer 1

pKb = 10.96

Step-by-step explanation:

Tartaric acid is a dyprotic acid. It reacts to water like this:

H₂Tart + H₂O ⇄ H₃O⁺ + HTart⁻ Ka1

HTart⁻ + H₂O ⇄ H₃O⁺ + Tart⁻² Ka2

When we anaylse the base, we have

Tart⁻² + H₂O ⇄ OH⁻ + HTart⁻ Kb1

HTart⁻ + H₂O ⇄ OH⁻ + H₂Tart Kb2

Remember that Ka1 . Kb2 = Kw, plus pKa1 + pKb2 = 14

Kb2 = Kw / Ka1 → 1×10⁻¹⁴ / 9.20×10⁻⁴ = 1.08×10⁻¹¹

so pKb = - log Kb2 → - log 1.08×10⁻¹¹ = 10.96