Mass Percent of NaCl dissolved in H2O

Question

When 50.0g of NaCl(s) is dissolved in 350. mL of water (density: 1.00 g/mL), the percent by mass of this solution is:

Mass percent: grams of solute / grams of solution * 100%

Mass percent: 50.0g NaCl(s) / 350 mL= 0.142 * 100 = 14.2

Mass percent= 14.2%

*answer is coming back as incorrect, what am I doing wrong?

Answer 1

What you are doing wrong is NOT using the correct mass of the SOLUTION.

The mass of the SOLUTE is 50.0. g

The mass of the SOLVENT is 350. ml x 1 g / ml = 350. g

The mass of the SOLUTION is 50.0 g + 350. g = 400 g

Mass % = 50.0 g / 400. g (x100%) = 12.5%