CHEMISTRY
posted by Maria .
A student needed to standardize a solution of NaOH which was approximately 0.125 M. The student carefully prepared the titration setup, but after 25 mL of NaOH was added, what was the pH of solution if initially flask contains 25 mL of 0.250 M HCl solution?

Write the equation and balance it. Then calculate the number of moles HCl initially, then number of moles NaOH added after 25 mL. Subtract the obtain the HCl concn and pH from there.

is the equation NaOH + HCl> NaCl + H2O?
I do not understand "Subtract the obtain the HCl concn." How do I calculate the HCl concn? 
You subtract the moles of NaoH from the moles of HCl to determine the excess moles left, which decides the pH.
To find pH,
pH= log(concent. of H+) or ( concen. of OH)
If NaOH is more than HCl, you get find pH by subtracting the pOH you get from the above formula from 14.