120 g of a solution with a mass fraction of 10% was evaporated to 80 g. What is the mass fraction of salt in one stripped off solution.

Given:
w1 (solution) = 10%
m1 (solution) = 120 g
m2 (solution) = 80 g
Need to know: w2 (solution)
Solution:
To begin with, we calculate the mass of a soluble substance contained in 120 g of a 10% solution: m1 (solutions) = m1 (solution) ∙ w1 (solution) / 100% = 120 g ∙ 10% / 100% = 12 g
let’s calculate the concentration of the solution, taking into account the evaporation of the solution up to 80g:
w2 (solution) = m2 (solution) ∙ 100% / m2 (solution) = 12g * 100% / 80g. = 15%
Answer: w2 (solution) = 15%