The volume of water in ml, which is needed to prepare a solution with a mass fraction of 12.5% from 25 g of NaCl is …

In this solution, 25 grams of salt will have a mass fraction of 25%.

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

The mass of the solution is 25 / 0.125 = 200 grams;

To find the mass of water, subtract the mass of salt from the mass of the solution:

m of water = 200 – 25 = 175 grams;

The density of water is 1 gram / cm3. To prepare this solution, measure 175 milliliters of water.

Check: 175 + 25 = 200;