[ILoveISO]

I am doing a strong base/strong acid titration and I graphed it out I have the ph and volume at the equivalence point but now what do I do to find out the exact molarity of base added?

I am given the molarity of HCL which is 0.100M, do I multiply that by the amount that was put into the beaker? (25ml) then divide that by the volume of NaOH used to get it to pH 7 and that will give me the exact molarity of NaOH?

[Matias Ekstrand]

Yes. You can do that because you translate n(HCl) to n(NaOH) through the mole relationship in the chemical equation.

[ILoveISO]

How about finding the exact molarity of unknown diprotic acid?

[Matias Ekstrand]

In your example your equivalence point was at pH 7.

When titrating on diprotic acids, you will have two places on your graph that shows a rapid increase in pH (equivalence points). At the first one, you have added exactly as much base as there was diprotic acid (only monoprotic acid left at that point). Use the same calculations as you did on your example. At the second equivalence point you have added double the amount of base compared to the acid in your original sample.

If you need to be sure about the concentration, use the second equivalence point as well and take a mean of the two calculations.

[ILoveISO]

Not even sure if my equivalence points are even accurate I just took the dot that is straight that went up...like ones at 15ml and the 2nd point is at 32.20ml

[Borek]

When titrating on diprotic acids, you will have two places on your graph that shows a rapid increase in pH (equivalence points).

Urban legend. It depends on the relative strengths of both protons. You may see separate end points, you may see one end point.

[Matias Ekstrand]

When titrating on diprotic acids, you will have two places on your graph that shows a rapid increase in pH (equivalence points).

Urban legend. It depends on the relative strengths of both protons. You may see separate end points, you may see one end point.

Interesting.

I suppose that one end point occurs when pK_a1 and pK_a2 are close to each other?

[Borek]

Even 3 units difference doesn't guarantee two separate endpoints, but a lot depends not only on the difference but also on absolute strength of acid. Sulfuric acid has pKa1 = -3 and pKa2 = 2 and it has one end point only. Oxalic acid has pKa1 = 1.25 and pKa2 = 4.27, so three units difference and first end point is barely visible.