The mass of table salt, which must be added to 70 g of a 2% NaCl solution to obtain a 6% solution, is …

1. Let’s calculate the mass of sodium chloride in the first solution:

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

m1 (NaCl) = 0.02 * 70 = 1.4 g

2.Let x = the mass of the added salt, then the mass of the resulting solution:

m2 (solution) = m1 (solution) + x = 70 + x;

3.express the total mass of salt:

m2 (NaCl) = m1 (NaCl) + x = 1.4 + x;

4.we write down the expression for calculating the mass fraction:

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

5. find the mass of added chloride – x:

0.06 = (1.4 + x): (70 + x);

(70 + x) * 0.06 = 1.4 + x;

2.8 = 0.94x

x = 2.98, that is, m2 (NaCl) = 2.98 g.

Answer: 2.98 g.