Calculate the mass fraction of sodium chloride if 350 g of water was dissolved in 8 mol of the substance.

Given:
m (H2O) = 350 g
n (NaCl) = 8 mol

To find:
ω (NaCl) -?

Decision:
1) Calculate the molar mass of NaCl:
M (NaCl) = Mr (NaCl) = Ar (Na) + Ar (Cl) = 23 + 35.5 = 58.5 g / mol;
2) Calculate the mass of NaCl:
m (NaCl) = n (NaCl) * M (NaCl) = 8 * 58.5 = 468 g;
3) Calculate the mass of the NaCl solution:
m solution (NaCl) = m (NaCl) + m (H2O) = 468 + 350 = 818 g;
4) Calculate the mass fraction of NaCl in the solution:
ω (NaCl) = m (NaCl) * 100% / m solution (NaCl) = 468 * 100% / 818 = 57.2%.

Answer: The mass fraction of NaCl in the solution is 57.2%.