A solution is 40% acetic acid by mass. The density of this solution is 1.049 g/mL. Calcu- late the mass of pure acetic acid in 120 mL of this solution at 20 C.

Answer 1

40% means 40 g acetic acid/100 g soln.
The density is 1.049; therefore, the volume of 100 g soln is 100/1.049 = 95.328 mL. You want 120 mL of the solution; therefore,
40 x (120 mL/95.328 mL) = ?? g in 120 mL.
To check you answer, convert 120 mL to grams and divide (??g/g)*100 soln = should be 40

Answer 2

Calculate what the mass of 120mL of the solution would be, then take 40% of that calculated mass. The resulting figure is the mass of pure acetic acid in the solution.