Respuesta :
					                   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
					                
					                
					             