The mass of silicic acid, which theoretically can be obtained by interaction with hydrochloric acid

The mass of silicic acid, which theoretically can be obtained by interaction with hydrochloric acid, 15.25 g of sodium silicate containing 20 percent of the impurity will be.

Given:
m tech. (Na2SiO3) = 15.25 g
ω approx. = 20%

To find:
m (H2SiO3) -?

Solution:
1) Na2SiO3 + 2HCl => H2SiO3 + 2NaCl;
2) ω (Na2SiO3) = 100% – ω approx. = 100% – 20% = 80%;
3) m (Na2SiO3) = ω * m tech. / 100% = 80% * 15.25 / 100% = 12.2 g;
4) n (Na2SiO3) = m / M = 12.2 / 122 = 0.1 mol;
5) n (H2SiO3) = n (Na2SiO3) = 0.1 mol;
6) m (H2SiO3) = n * M = 0.1 * 78 = 7.8 g.

Answer: The mass of H2SiO3 is 7.8 g.