What mass of salt must be added to 80 g of water to obtain a 20% salt solution?

In this solution, 80 grams of water will have a mass fraction of 80%.

Find the mass of the solution by dividing the mass of water by its mass fraction.

m solution = 80 / 0.8 = 100 grams;

Let us find the mass of salt by subtracting the mass of water from the mass of the solution.

m salt = 100 – 80 = 20 grams;

Check: 20 + 80 = 100;