Question

Find the percent by mass of sodium chloride in a 1.45M NaCl solution. The density of the solution is 1.05g/mol .

Answer 1

(Note: I don't think the density is 1.05 g/mol; rather, I think it is 1.05 g/mL)
Percent by mass means grams solute per 100 g solution.
molarity = moles/L of solution. So we change molarity to grams and L of solution to total mass.

1.45 M NaCl = 1.45 moles/L. 1.45 moles NaCl x molar mass NaCl = ?? grams NaCl.

How much does a liter of solution weigh?
1.05 g/mL x 1000 mL = 1050 grams.

So we have ??g NaCl/1050 grams solution and multiply by 100 to change to percent.