Determine m Nacl and m H2O for the preparation of 400 g of 20% Nacl solution.

Let’s calculate the weight of the dissolved salt.
M salt = 400 x 0.2 = 80 grams;
Similarly, we find the weight of the solvent (water).
(In calculations, we take the density of water equal to 1 gram / ml).
M water = 400 x 0.8 = 320 grams = 320 ml;
Let’s check. To do this, add the masses of the components of the solution and get the mass of the solution in question.
80 + 320 = 400;