Step 1
% by mass is defined as:
mass of solute ----- 100 g of solution
Solution = solute + solvent
Solute = NaCl
Solvent = Water (H2O)
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Step 2
Mass of solution = 37.5 g (NaCl) + 137.5 g (water) = 175 g
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Step 3
Procedure:
37.5 g NaCl ----- 175 g solution
X ----- 100 g solution
X = 100 g solution x 37.5 g NaCl/175 g solution = 21.4 g NaCl = 21.4 % by mass
Answer: % by mass = 21.4 %