Derivation of Equation 9-10 for pH of the intermediate form Na+ HA-. The derivation in the chapter was for HL, the intermediate form of H2L+. Write the mass and charge balances for Na+ HA- at formal concentration F. Substitute [H2A] + [HA-] + [A2-] for [Na+] in the charge balance. After canceling like terms on both sides of the charge balance, express all concentrations in terms of [HA-] and [H+]. Solve for [H+] and show that you end up with the same expression as Equation 9-10.