Question

A 20.0 gram sample is a mixture of sodium phosphate ,sodium mono-hydrogen phosphate,sodium dihydrogen phosphate and sodium chloride. The sample is dissolved in 100.0 ml of deionized water and titrated with 1.5 M hydrochloric acid. The initial pH of the solution is pH= 12.9. The first equivalence point occurs at 16.0 ml of acid ( pH= 10.5). The second equivalence occurs after the addition of an additional 44.0 ml of acid( pH= 8.05). The third equivalence occurs after the addition of an additional 11.1 ml of acid( pH= 1.22). Calculate the mass percent of each component in the mixture.