Find the percent by mass of sodium chloride in a 1.15M NaCl solution. The density of the solution is 1.07g/mL.

Answer 1

1.15 M NaCl = 1.15 mols/L of solution.
How many grams is 1.15 mols? That will be 1.15 mols x molar mass NaCl = approximately 67.3 g/L.
How much does the L of solution weigh? It will weigh (has a mass of) 1.07 g/mL x 1000 mL = 1070 g.
So our solution is 67.3 g NaCl/1070 g soln = approximately 0.063 g NaCl/g soln. Multiply that by 100 to obtain the g/100 which is the percent or approximately 6.3%. You need to check my work carefully and do the math better. I just estimated. Also watch the number of significant figures if your prof is picky about that.