To 300 g of a 5% salt solution was added 30 g of salt. Calculate the mass fraction of the substance in the solution.

1. Find the mass of salt in the first solution:

m1 (salt) = m1 (solution) * w1 (salt);

m1 (salt) = 300 * 0.05 = 15 g;

2.when adding salt, the masses characterizing the solution will change:

m2 (salt) = m1 (salt) + m (add salt);

m2 (salt) = = 15 + 30 = 45 g;

m2 (solution) = m1 (solution) + m (add salt);

m2 (solution) = 300 + 30 = 330 g;

3. mass fraction of salt in the resulting solution:

w2 (salt) = m2 (salt): m2 (solution);

w2 (salts) = 45: 330 = 0.1364 or 13.64%.

Answer: 0.1364 or 13.64%.