A soft drink contains 28 mg of sodium in 305 g of H2O?

Question

What  the concentration of sodium in the soft drink in mass percent?

Answer 1

28 mg x 1 g/1000 mg = 0.028 g

Total mass of soln = 0.028 g + 305 g = 305.028 g

% Sodium by mass = 0.028/305.028 (100)=0.00918% = 0.0092% (2significant figures). 

Answer 2

Convert the 305g of H₂O to mg by multiplying by 1000.

So, the percentage of sodium will be 28/(28+305000).