What is the mass fraction of sugar in a solution obtained by evaporating 200 g of a 20% solution to 70 g?

Let’s find the mass of sugar in this solution. The mass of sugar will be equal to the product of the mass of the solution by the mass fraction of sugar.

M sugar = 200 x 0.2 = 40 grams;

After evaporation, the solution will weigh not 200, but 70 grams. The amount of sugar in it will not change.

Let’s find the mass fraction of sugar in the new solution:

With sugar = 40/70 = 0.5714 = 57.14%;