Concentration of Solutions

Name Class Date
Problem Solving continued
Sample Problem 4
Determine the molal concentration of a solution containing 81.3 g of
ethylene glycol, HOCH 2 CH 2 OH, dissolved in 166 g of water.
Solution
ANALYZE
What is given in the problem?
What are you asked to find?
the mass of ethylene glycol dissolved, and the
mass of the solvent, water
the molal concentration of the solution
Items
Mass of solute
Molar mass of solute
Moles of solute
Mass of solvent
Concentration (molality)
Data
81.3 g ethylene glycol
62.08 g/mol ethylene glycol
? mol ethylene glycol
166 g H 2 O
? m
PLAN
What steps are needed to calculate the molal concentration of the ethylene glycol
solution?
Determine the amount of solute in moles and the mass of solvent in kilograms;
calculate the moles of solute per kilogram of solvent.
1
Mass of C 2
H 6
O 2
in g
multiply by the
inverted molar
mass of C 2
H 6
O 2
2
Amount of C 2
H 6
O 2
in mol
moles C 2
H 6
O
m
2
kg H 2
O
5
Molality of C 2
H 6
O 2
solution
3
Mass of H 2
O in g
multiply by the
conversion factor
1 kg
1000 g
4
Mass of H 2
O in kg
1
molar mass of C 2
H 6
O 2
given 1 mol C 2
H 6
O 2 mol C2 H 6
O 2
g C 2
H 6
O 2
62.08 g C2 H 6
O 2
given 1 kg
g H 2
O kg H2 O
1000 g
calculated above
mol C 2
H 6
O 2
m C 2
H 6
O 2
solution
kg H 2
O
calculated above
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Holt ChemFile: Problem-Solving Workbook 207 Concentration of Solutionss