How many grams of NaCl should be taken to prepare 40 g of a 30% solution?

The mass of the solution is 40 grams;

To find the mass of salt, it is necessary to multiply its mass fraction by the mass of the solution.

m salt = 40 x 0.3 = 12 grams;

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

m of water = 40 – 12 = 28 grams;

The density of water is 1 gram / cm3. To prepare this solution, you need to measure out 28 milliliters of water.

Check: 28 + 12 = 40;