Citric acid, H3C6H5O7, is present in citrus fruits. It is a triprotic acid (i.e. it can donate three protons per molecule in an acid-base reaction) with acid- dissociation-constant values of Ka1 = 7.4 x 10-4, Ka2 = 1.7 x 10-5, and Ka3 = 4.0 x 10-7. Write the balanced equations for the three acid-dissociation equilibria. Calculate the pH of a 0.050 M solution of citric acid. Explain any approximations or assumptions that you make in your calculation.

Give it a try. You already know the formula, H3C6H5O7. Take off one proton (a proton is H(+)). What do you get? H2C6H5O7(+) + H(+). Try it again for the second and third protos.