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

What the other people had said

Answer 2

Answer:

pKb = 10.96

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