Question

1. 
2. (1) The Ka values for citric acid (2) and phosphoric acid
3. (3) The exact concentration of the citric acid and (4) phosphoric acid

Citric Acid Titration 12 10 2 40 60 20 80 volume NaOH (mL) Phosphoric acid Titration 12 r 10 ds 4 25 50 75 vol NaOH (mL)

Answer 1

(1) pKa1 = 3.14, Ka1 = 7.244 × 10^-4

pKa2 = 4.77, Ka2 = 1.7 × 10^-5

(2) pKa1 = 2.12, Ka1 = 7.52 × 10^-3

pKa2 = 7.21, Ka2 = 6.23 × 10^-8

(3) Initial pH = 2.05 of Citric acid, [H+]= 10^-2.05 M,

[Citrate -] = [H+]= 10^-2.05 M

[Citric acid] = [H+][Citrate -]/ Ka1

= 10^-2.05 × 10^-2.05 / 7.244 × 10^-4 =

[Citric acid] = 0.109 M

(4) Initial pH 2.05 of H3PO4 , [ H+]= 10^-2.05 M,

[H3PO4] = 10^-2.05 × 10^-2.05 / 7.52 × 10^{-3 =} 0.0105 M