30 g of common salt was dissolved in 170 g of water. Find the mass fraction (in%) of the salt in the resulting solution.

Given:
m (NaCl) = 30 g
m (H2O) = 170 g

To find:
ω (NaCl) -?

Decision:
1) Calculate the mass of the resulting solution:
m solution (NaCl) = m (NaCl) + m (H2O) = 30 + 170 = 200 g;
2) Calculate the mass fraction of NaCl in the resulting solution:
ω (NaCl) = m (NaCl) * 100% / m solution (NaCl) = 30 * 100% / 200 = 15%.

Answer: The mass fraction of NaCl is 15%.