A student adds 25.00mL of distilled water to a 10.00mL sample of HCl of an unknown molarity and titrates this against a 0.085M NaOH solution. Will the addition of the water interfere with the determination of the molarity of the HCl sample? Why or why not?

Answer 1

No, it will not.
The whole concept of a titration is that the indicator will turn when mols base = mols acid. Add water does not change the number of mols acid or base. Remember mols acid or base = M x L = mols.
When I demonstrated a titration to my students I always used water liberally to wash down the sides of the titration flask. And, of course, waited for the obvious remark of "but doesn't that dilute the acid in the flask" to which I always replied, "yes it does but doesn't it dilute the base at the same time?" So the answer is either
1. Yes, it dilutes the acid but it also dilutes the base so the result evens out, or,
2. It doesn't matter since mols acid = mols base is when the indicator changes and adding water doesn't change mols acid or base.