Calculate the mass of the solute in 80 g of caustic soda solution with a mass fraction of solute of 40%.

In order to find the mass of a solute, it is necessary to multiply its mass fraction by the mass of the solution.

M alkali = 80 x 0.4 = 32 grams;

Similarly, we find the mass of water. We multiply the mass of the solution by the mass fraction of water in it.

M water = 80 x (1 – 0.4) = 48 grams;

Check: M solution = M water + M alkali = 32 + 48 = 80;