[karol.s]

hello, Can somebody help wit the following problem?

determine pH in the 2nd equivalence point of a Titrate mixture of 0.05Ma HCl 50ml and H3PO4 with standard NaOH 0.04 Ma solution, the first equivalence point was reached after 13,66 ml of base, and the second equivalence point after 16,28 ml of base.

[billnotgatez]

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[karol.s]

C Na2HPO4 = (16.28ml -13.66ml) x 0.04 / vt
                  = 1.58 x 10-3

(H3O+) = root (( 1x10-14 + C Na2HPO4 x ka3)/(1+C Na2HPO4/ ka2))

pH= -log (H3O+)

but I don't know if this is correct