If 7.89 mL of a sodium hydroxide solution can neutralize 13.1 mL of 0.293 M HCl, what volume of 0.765 M HBr can be neutralized by 15.4 mL of the same sodium hydroxide solution?

9.79 mL Both HCl and HBr are neutralized by NaOH on a mole per mole basis. So a constant volume of a sodium hydroxide solution will neutralize the same number of moles of either HCl or HBr. So here are the equations to represent what we know and what we want. X = molarity of the Sodium Hydroxide solution and Y = volume of HBr solution to be neutralized. 13.1 * 0.293 = 7.89 * X Y * 0.765 = 15.4 * X Solve the first equation for X. 13.1 * 0.293 = 7.89 * X 3.8383 = 7.89 * X 0.486476553 = X Now substitute the known value of X into the 2nd equation and solve for Y. Y * 0.765 = 15.4 * 0.486476553 Y * 0.765 = 7.49173891 Y = 9.793122758 Round to 3 significant figures, getting 9.79 ml