Question

For the diprotic weak acid H2A, Ka1 = 2.1 x 10^-6 and Ka2 = 5.1 x 10^-9. What is the pH of a 0.0600 M solution of H2A? What are the equilibrium concentrations of H2A and A2- in this solution? STRATEGY: Start by making a table for the molar concentrations after the first dissociation step. H2A(aq) ⇌ H+(aq) + HA−(aq) Initial: 0.0600, 0, 0 Change: -x, +x, +x Express Ka1 in terms of x, and then show the simplified expressions (when x is assumed to be negligible compared to the initial concentration). Ka1 = (A/B) = (C/D) A and B are complete, C and D are simplified. numerator A in complete expression: ? denominator B in complete expression: ? numerator C in simplified expression: ? denominator D in simplified expression: ? Also, give the numerical value of x using the appropriate approximation. What is the pH of the solution if you stopped here? x=? pH=?

          For the diprotic weak acid H2A, Ka1 = 2.1 x 10^-6 and Ka2 = 5.1 x 10^-9. What is the pH of a 0.0600 M solution of H2A? What are the equilibrium concentrations of H2A and A2- in this solution?

STRATEGY: Start by making a table for the molar concentrations after the first dissociation step.

H2A(aq) ⇌ H+(aq) + HA−(aq)
Initial: 0.0600, 0, 0
Change: -x, +x, +x

Express Ka1 in terms of x, and then show the simplified expressions (when x is assumed to be negligible compared to the initial concentration). Ka1 = (A/B) = (C/D)

A and B are complete, C and D are simplified.

numerator A in complete expression: ?
denominator B in complete expression: ?
numerator C in simplified expression: ?
denominator D in simplified expression: ?

Also, give the numerical value of x using the appropriate approximation. What is the pH of the solution if you stopped here?
x=?
pH=?

Added by Daniel P.

Question

Please give Ace some feedback