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The values of pKa1 and pKa2 of malonic acid are 2.85 and 5.70 respectively. Calculate the pH of the first and second equivalence points of the titration of 10cm^3 of malonic acid of concentration 0.1 M with sodium hydroxide of concentration 0.1 M.

my attempt at a solution:

maximum buffering capacity before first endpoint: pH=pKa1 = 2.85

[OH-] = [(Kw/Ka1)*(0.05)]^(0.5)

therefore pOH = 6.23

pH = 14-6.23 = 7.77

im stuck here as the answer given for the pH of the first endpoint is 3.50 and I have no idea how to work it out