Question

A 29.00 mL sample of an unknown H3PO4 solution is titrated with a 0.130 M NaOH solution. The equivalence point is reached when 27.73 mL of NaOH solution is added.

Answer 1

I am first assuming that you want the molarity of the acid. Use the formula $M_{a} V_{a} = M_{b}V_{b}$ which is the titration formula. M is molarity (a is of acid and b is of base) and V is volume in mL (a is of acid and b is of base).  Plugging in gives us $(29 mL)(M_{a}) = (0.130 M)(27.73 mL)$. Solving gives us $M_{a} = 0.124 M$