The amount of calcium nitrate substance required to prepare 820 g of a solution with a mass fraction of salt of 4% is …

The mass of the solution is 820 grams;

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

m salt = 820 x 0.04 = 32.8 grams;

Let’s find the amount of substance in this mass of calcium nitrate.

M Ca (NO3) 2 = 40 + (14 +16 x 3) x 2 = 164 grams / mol;

m Ca (NO3) 2 = 32.8 / 164 = 0.2 mol