The expression used to calculate the mass percent concentration is: % (m/m) = (mass of solute) / (mass of solution (solute + solvent)) x 100.
First let's transform mL into grams of water:
1 g of water ---- 1 mL of water
x g of water ---- 170 mL of water
x = 170 g of water
Now let's calculate the mass of solution:
mass of solute = 30 g of NaCl
mass of solvent = 170 g of water
solute + solvent = 30 + 170 = 200 g
% (m/m) = (mass of solute) / (mass of solution (solute + solvent)) x 100.
% (m/m) = (30g/200g) x 100.
% (m/m) = 15.0%
Answer: 15.0%