pH = 1.1
First, determine how many moles of each reactant was used
Moles HBr = 0.0500 l * 0.15 mol/l = 0.0075 mol
Moles KOH = 0.0110 l * 0.25 mol/l = 0.00275 mol
Now determine how much acid (HBr) is left over after the rest of it is neutralized by the KOH. A simple matter of subtraction.
0.0075 - 0.00275 = 0.00475 mol
Now determine the molarity of HBr. That would be moles per volume, so
0.00475 mol / (0.0500 l + 0.0110 l)
= 0.00475 mol / 0.061 l
= 0.077868852 mol/l
= 0.077868852 m
Now since HBr is a strong acid, it will completely dissociate into H+ and Br- ions. So the molarity of the H+ ions will be the same as the molarity of HBr. And the definition of pH is
pH = - log(H+)
So the log of 0.077868852 is -1.108636228
And the negation of that is 1.108636228
So the pH is 1.1 to 2 significant figures since that's the precision of the data we were given.
