To 70 g of a solution with a mass fraction of calcium chloride of 40% was added 18 ml of water and 12 g of the same salt

To 70 g of a solution with a mass fraction of calcium chloride of 40% was added 18 ml of water and 12 g of the same salt. Mass fraction of salt in the resulting solution is equal to

The density of water is 1 g / ml. This means that the mass of water, expressed in grams, is numerically equal to the volume of water expressed in milliliters. Those. the mass of added water is 18 g.

We calculate the mass of calcium chloride in the original 40% solution:

m (1) (CaCl2) = 40% ∙ 70 g / 100% = 28 g,

The total mass of calcium chloride in the final solution is equal to the sum of the masses of calcium chloride in the initial solution and the added calcium chloride. Those.

m (total) (CaCl2) = 28 g + 12 g = 40 g,

The mass of the final solution is equal to the sum of the masses of the initial solution and the added water and salt:

m (total). (r-ra CaCl2) = 70 g + 18 g + 12 g = 100 g,

Thus, the mass fraction of salt in the final solution is equal to:

w (3) (CaCl2) = 100% ∙ mtotal (CaCl2) / mtotal (CaCl2 solution) = 100% ∙ 40/100 = 40%