Question 1159198: How much water must be evaporated from 80 pounds of a 12% solution of salt in order to obtain a
20% solution? Answer by ikleyn(52847) (Show Source):
Let W be the MASS of water to evaporate, in pounds.
The amount of salt in the original 80 pounds of the 12% solution was 0.12*80 = 9.6 pounds.
When W pounds of water were evaporated, the remaining mass became 80 pounds - W pounds.
We want the new salt concentration be 20%. It means
= 0.2. (1)
(Notice that when the water evaporates, the mass of salt REMAINS the SAME (!) )
To solve equation (1), multiply both sides by (80-W). You will get
9.6 = 0.2*(80-W).
Simplify and find W.
9.6 = 0.2*80 - 0.2W
0.2W = 0.2*80 - 9.6 = 6.4,
W = = 32 pounds.
ANSWER. 32 pounds of water should be evaporated.
CHECK. I will check equation (1) for the concentration
= = 0.2, which is precisely correct (!)
