You begin with a 400 ml of pure water (assume the density of the water is 1 g cm-3), and make a solution of 7 % salt (NaCl) by mass.
1. What is the mass of the water?
2. What is the mass of the salt in your solution?
3. After the evaporation, your solution lost 100 g of mass. How much salt (NaCl) is left in the solution?
4. What is the salinity (in parts-per-thousand, or ppt) of this new solution?