Determine the mass fraction of potassium hydroxide in a solution of 25 g of KOH in 250 cm3 of water.

The weight of the solution will be the weight of the alkali and the weight of the water.

The density of the water is 1 gram / ml. Therefore, the mass of water will be 250 x 1 = 250 grams.

The weight of the solution will be equal to:

M solution = m alkali + m water = 25 + 250 = 275 grams;

The mass fraction of alkali will be equal to the ratio of the weight of the alkali to the weight of the solution.

With alkali = m alkali / m solution = 25/275 = 0.091 = 9.1%;