100 g of water was dissolved in 31.6 g of potassium nitrate. Calculate the percentage of solute in the solution of this salt.

Percentage concentration of a solute (mass fraction of a substance in a solution) is the ratio of the mass of a solute to the total mass of a solution.
w = m substance: m solution
The mass of the solution is calculated as the sum of the mass of the solute and the solvent.
m solution = m solute + m solvent
Usually the mass fraction is expressed as a percentage.
We calculate the mass of the solution:
m solution = m (KNO3) + m (H2O) = 31.6 + 100 = 131.6 (g)
We calculate the percentage concentration of the solution:
w (KNO3) = (m (KNO3): m solution) x 100% = 24%
Answer: Percentage concentration of solute 24%