Question

Worksheet 19 Titration of Polyprotic Acids Name: 1. Calculate the sulfite ion [SO3'] concentration in a 0.123 M solution of the weak acid, sulfurous acid (H2SO3). The stepwise dissociation constants of carbonic acid are: Ka1 1.41 x 102 Ka2-6.31 x 108 3. Consider the following dissociation of the triprotic acid, phosphoric acid (HsPOs): Step 1 H3POa + H2O <=> H30+ + H2PO4, Step 2 HP0i + H2O <=> H30+ + HP042- Step 3 HPO42-+ H2O <-> H3O+ + PO43- Kal=7.1 x 10-3 Ka2-6.3 x 10-8 Kg = 4.2 x 10-13 Briefly explain how the [Hs0'] and the pH of a 0.458 M H3PO4 can be calculated using the given Ka's. State your assumptions and explain your justification for using your assumptions. At equilibrium, estimate the molar concentration of HPo,2 and PO,3 ions in the solution.

Answer 1

Ka, I o-123 0.123- e x wUb-ium concen