A 520-gram sample of seawater contains 0.317 moles of NaCl. What is the percent composition of NaCl in the water?

A. 1.1%

B. 2.8%

C. 3.6%

D. 6.1%

Answer: option c. 3.6%

Explanation:

1) Definition (formula)

Percent composition = (mass of solute / mass of solution) * 100.

2) Mass of solution = mass of seawater = 520 g.

3) Mass of solute

a) mass = molar mass * number of moles

b) The molar mass of NaCl may be calculated using the atomic masses of the elements given in a periodic table: 22.990 g/mol + 35.453 g/mol = 58.443 g/mol

c) mass of NaCl = 58.443 g/mol * 0.317 mol = 18.53 g.

d) Percent composition = (18.53 g / 520 g) * 100 = 3.6% ← answer