Question

HELP PLEASE!

I have 40ml of DI water with 5ml of phosphoric acid titrated with 0.0759M of NaOH. My first equivalence point is 6.75ml and my second equivalence point is 13.5ml of NaOH. The first equivalence point pH is 2.58 and the second half equivalence pH is 4.9.

What would be the concentration of phosphoric acid?

Answer 1

Phosphoric acid neutralizes in three stages.

First equivalent point:

H3PO4 + NaOH -> NaH2PO4 + H2O

Use first equivalence point, amount of moles
Of phosphoric acid and NaOH are equal

Answer 2

thats the part I was missing! forgot that the number of moles were equal. thanks @Gebooors!