80 grams of an 80% solution was evaporated until 20 grams of water had evaporated.

80 grams of an 80% solution was evaporated until 20 grams of water had evaporated. determine the mass fraction of the substance obtained in the solution.

1) Find the mass of water and solute in an 8% solution:
mass fraction of solute in solution = mass of substance: mass of solution * 100%.

Therefore, the 8% solution contains:
8% = x: 80 g * 100%, so x = 8%: 100% * 80 = 6.4 g of solute.

2) The mass of the solution, after evaporation, is equal to: 80 – 20 = 60 g.

3) The new mass fraction of the solute, in the solution, is = 6.4: 60 * 100 = 10.7%.

Answer: the concentration of the resulting solution is 10.7 percent.