Sodium sulfate weighing 40 grams was dissolved in 160 ml of water. What is the mass fraction of salt in the resulting solution.

Given:
m (Na2SO4) = 40 g
V (H2O) = 160 ml
ρ (H2O) = 1 g / ml

To find:
ω (Na2SO4) -?

Decision:
1) Calculate the mass of water:
m (H2O) = ρ (H2O) * V (H2O) = 1 * 160 = 160 g;
2) Calculate the mass of the resulting sodium sulfate solution:
m solution (Na2SO4) = m (Na2SO4) + m (H2O) = 40 + 160 = 200 g;
3) Calculate the mass fraction of sodium sulfate in the resulting solution:
ω (Na2SO4) = m (Na2SO4) * 100% / m solution (Na2SO4) = 40 * 100% / 200 = 20%.

Answer: The mass fraction of sodium sulfate in the resulting solution is 20%.