How to calculate pH please

What is the pH in the titration of 77 mL of 0.1 M HCl with 0.1 M NaOH after the addition of 62 mL 0.1 M NaOH.

pH = -log[H+] that is, pH = the negative base 10 logarithm of the concentration of hydrogen ions in a solution in moles per litre.

HCl reacts with NaOH in the following reaction:
HCl(aq) + NaOH(aq) --> NaCl(aq) + H2O(l) therefore 1 mol HCl reacts with 1 mol NaOH

0.077L * 0.1M = 0.0077mol HCl
0.062L * 0.1M = 0.0062mol NaOH

0.0062mol NaOH reacts with 0.0062 mol HCl, leaving 0.0015mol HCl (0.0077 - 0.0062 = 0.0015)

Now we just work out the concentration:
Total volume = 0.062L + 0.077L = 0.139L
Concentration = amount of solute / volume of solution, therefore 0.0015 / 0.139 = 0.010791M HCl
Since HCl is a strong acid and donates all it's protons, the concentration of H+ = 0.010791M

Now that we have the concentration of hydrogen, -log10(0.010791) = 1.967
So the pH is roughly 2. Hope this helped :)

sir....you can use pH-meter to calculate the PH for any solution but before that you must calibrate the instrument.