Acid solution problem

Question

Theresa Morgan, a chemist, has a 30% hydrochloric acid solution and a 65% hydrochloric acid solution. How many liters of each should she mix to get 735 liters of a hydrochloric acid solution with a 60% acid concentration?

Answer 1

Let a be volume of 30% and b be volume of 65% solution. You can generate two equations for the two unknowns by doing a volume balance (assume volumes are additive - usually reasonable for solutions of the same solute/solvent) and an HCl balance:

a + b = 735 Volume Balance

.3a + .65b = .6(735) HCl balance

You can use substitution of b = 735 - a into 2nd equation or you can solve by combining the equations in order to eliminate a variable.