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

Let’s calculate the mass of sugar and water in the initial solution. To do this, we multiply their mass fractions by the mass of the initial solution.

M sugar = 200 x 0.2 = 40 grams;

M water = 200 x 08 = 160 grams;

After evaporation, the mass of sugar in the solution will not decrease and will remain equal to 40 grams.

Its mass fraction will be equal to the ratio of the weight of sugar to the weight of the one stripped off solution:

With sugar = 40/70 = 0.571 = 57.1%;

The mass of water will decrease from 160 to 71 – 40 = 30 grams.