To 400 g of a solution containing 18% potassium chloride was added 500 ml of water.

To 400 g of a solution containing 18% potassium chloride was added 500 ml of water. Determine the mass fraction (in percent) of potassium chloride in the resulting solution.

1) The mass of the dissolved substance of potassium chloride in its solution is calculated by the formula: W = (mp.v-va / mp.pa) * 100%.
18 = (x / 400) * 100%.
x = 72g.
2) Calculate the mass of the solution after adding water. We are given the volume of water, but we need mass. Since the density of water is equal to one, the mass will be equal to the volume and equal to 500 g. Then the mass of the solution after adding water is equal to: 400 + 500 = 900g.
3) Mass fraction of potassium chloride in the resulting solution is: W = (72/900) * 100 = 8% – the answer.