Calculate the mass of water to be evaporated from 200 g of 2% sodium chloride solution to make the solution 10% w / w.

First, let’s find out what is the mass of chloride in solution:
2% = x / 200 * 100%.
Hence x = 4 g. The mass of salt after evaporation of water remains the same, only the mass fraction changes. The mass of water in the original solution:
m1 = 200 – 4 = 196 g.
Find the mass of the solution after evaporation of the water:
10% = 4 / y * 100%.
Y = 400/10 = 40 g. From this it follows that the mass of water in this solution:
m2 = 40 – 4 = 36 g.
Thus, the mass of water to be evaporated is:
m = m1 – m2 = 196 – 36 = 160 g.