Question

(Please help!) One way to describe the concentration of an acid is as a percent by volume. For example, in 40 mL of a 30% acid solution, the volume of pure acid is 40 x 30/100 or 12 mL, and the volume of water is 40-12 or 28 mL. If 5 mL of pure acid is mixed with 20 mL of water to give 25 mL of acid solution, the concentration of the solution is given by 5/25 x 100% = 20 %. If water is mixed with 50 mL of 40% acid solution, write an equation that describe the acid concentration, C(x), as a function of the volume of water added, x.

Answer 1

The answer is C(x) = (20/50 + x) x 100%, but why?