We have solution containing solutes obtained by sulfuric acid leaching of an ore. The concentration of sulfuric acid in the solution before the addition of ore is 2M. Due to the reaction of ore constitutents with sulfuric acid, sulfate compounds of corresponding metals are formed. We would like to determine the free acidity of the resulting leach solution.

It depends on how much acid reacted and how much is left. If you want the pH of the solution, use the formula:

pH = - log[H^+]

where [H^+] means concentration of H^+ ions.

Or, if you're trying to find the amount of usable Sulfuric acid is left, do the following.

Take a pH Test.

\frac{2}{10^{pH}}

That should approximate your Sulphuric Acid molarity remaining.

A very accurate method is to titrate a sample. Titration of an acid with NaOH is very accurate. I'd try 20.00 ml of your sample to be titrated with 1.00 M NaOH.
M(acid) x Volume(acid) = M(NaOH) x Volume(NaOH) This will give you the molarity of the hydrogen ions. Example .5M H+ x 1H2SO4/2H+ = .25 M H2SO4 remaining.