Question

Challenge Problem: An aqueous solution contains 167 g CuSO4 in 820 mL of solution. The density of the solution is 1.195 g/mL. Calculate the following: a. Molarity b. Percent by mass c. Mole fraction d. Molality of the solution

Answer 1

Answers:

a. 1.28 mol/L; b. 17.0 %; c. 0.0227; d. 1.29 mol/kg

Explanation:

a. Molar concentration

c = moles/litres

Moles = 167 × 1/159.61     Do the calculation

Moles = 1.046 mol

Litres = 820 × 1/1000      Do the calculation

Litres = 0.8200 L            Calculate the molar concentration

c = 1.046/0.8200            Do the division

c = 1.28 mol·L⁻¹

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b. Percent by mass

Mass % = mass of solute /mass of solution × 100 %

Mass of solution = volume × density     Insert the values

Mass of solution = 820 × 1.195               Do the multiplication

Mass of solution = 979.9 g                     Calculate the mass %

Mass % = 167/979.9 × 100                      Do the operations

Mass % = 17.0 %

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c. Mole fraction

χ = moles of solute/(moles of solvent + moles of solute)

Mass of solvent = mass of solution – mass of solute

Mass of solvent = 979.9 – 167         Do the subtraction

Mass of solvent = 812.9 g                Convert to moles

Moles of water = 812.9 × 1/18.02     Do the calculation

Moles of water = 45.11 mol              Calculate the total moles

Total moles = 1.046 + 45.11              Do the addition

Total moles = 46.16 mol                  Calculate the mole fraction

χ = 1.046/46.16                                  Do the division

χ = 0.0227

===============

d. Molal concentration

b = moles of solute/kilograms of solvent

Mass of solvent = 812.9 g = 0.8129 kg     Calculate the molal concentration

b = 1.046/0.8129                                         Do the division

b = 1.29 mol/kg