Math Question?

Question

A chemist mixed 40mL of 8% hydrochloric acid solution with 60mL of 12% hydrochloric acid solution. She used a portion of this resulting solution and replace it with distilled water. If the new solution tested 5.2% hydrochloric acid, how much of the original mixed solution did she use?

Answer 1

40mL @8% = 3.2mL HCl
60mL @12% = 7.2mL HCl

Mixture = 10.4mL HCl in 100mL (10.4%)

If the new solution had 5.2%, it was diluted by half, so she used half of the original solution.

Answer 2

volume of HCl (hydrochloric acid) = 40 x 8/100 + 60 x 12/100
= 10.4 mL

% HCl = 10.4 / 100 x 100
= 10.4%

10.4 x v x 100 = 5.2
Volume of HCl solution = 50mL