Question

An aqueous solution contains 4.3% NaCl by mass.

Part A

Calculate the molality of the solution.

Express your answer using two significant figures.

Part B

Calculate mole fraction of the solution.

Express your answer using two significant figures.

Answer 1

4.3% NaCl by mass
is 4.3 grams of NaCl / 100 total grams of mix
allowing us to say that's
4.3 grams of NaCl / 95.7 grams of H2O

use molar mass to find moles:
4.3 g NaCl divided by 58.44 g NaCl / mol = 0.07357 mol NaCl

A) Calculate the molality of the solution.
0.07357 mol NaCl / 0.0957 kg of H2O = 0.7688 molal

95.7 grams of H2O

use molar mass to find moles:
95.7 grams of H2O divided by 18.01 g H2O / mol = 5.31 mol H2O

total moles = 5.31 mol H2O + 0.07357 mol NaCl = 5.387 total moles

B) Calculate mole fraction of the solution
0.07357 mol NaCl / 5.387 total moles = 0.01365 mole fraction NaCl