What equation can I use to find the pH in this problem?

Question

I would like to know the general equation applied to this type of problem so that I can know how to do all questions like this. Also, I would like to see specifically how to work out this problem:

A 10.0 mL sample of HCl was titrated with 0.1 M NaOH to neutrality, and it took 7.2 NaOH. What was the pH of the gastric juice?

Thank you sincerely for all your help.

Answer 1

Volume = 0.01 L

You need the number of moles of HCl that you started with.

That is equal to the number of moles of NaOH needed to titrate because 1 mole of NaOH reacts with 1 mole of HCl.

0.0072 L x 0.1 mol / L = 0.00072 mol

0.00072 mol / 0.01 L = 0.072 M = [H(+)]

pH = - log(10) [H(+)] = 1.1