Physical Properties
of Solutions
Chapter 13
Lake Nyos, West Africa
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•
Earthquake?
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•
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Chemistry In Action: The Killer Lake
Lake Nyos, West Africa
Concentration Units
Concentration - amount of solute present in a given quantity
of solvent or solution:
• Mass percentage
• ppm and ppb
• Mole fraction
• Molarity
• Molality
Concentration Units
Mass percentage (w/w)
% by mass =
mass of solute
mass of solute + mass of solvent
mass of solute
=
mass of solution
x 100% (w/w)
Mole Fraction (X)
moles of A
XA =
sum of moles of all components
x 100%
Concentration Units
Parts per million (ppm)
mass solute
ppm 
x 10 6
mass soln
Parts per billion (ppb)
mass solute
ppm 
x 10 9
mass soln
Concentration Units
Molarity (M)
moles of solute
M =
liters of solution
Molality (m)
moles of solute
m =
mass of solvent (kg)
Practice Exercise p 544
What is the molality of a solution made by dissolving 36.5 g
of naphthalene (C10H8) in 425 g of toluene (C7H8)?
Answer: 0.671 m
What is the molality of a 5.86 M ethanol (C2H5OH)
solution whose density is 0.927 g/mL?
moles of solute
moles of solute
m =
M =
mass of solvent (kg)
liters of solution
5.86 moles ethanol = 270 g ethanol
Assume 1 L of solution:
(0.927 g/mL) (1000 mL) = 927 g of solution
mass of solvent = mass of solution – mass of solute
= 927 g – 270 g = 657 g = 0.657 kg
moles of solute
m =
mass of solvent (kg)
=
5.86 moles C2H5OH
0.657 kg solvent
= 8.92 m
Practice Exercise p 543
(a) Calculate the mass percentage of NaCl in a solution
containing 1.50 g of NaCl in 50.0 g of water.
(b) A commercial bleaching solution contains 3.62 %(w/w)
sodium hypochlorite, NaOCl. What is the mass of NaOCl
in a bottle containing 2.50 kg of bleaching solution?
Answer:
(a) 2.91%
(b) 90.5 g of NaOCl
Sample Exercise 13.6 Calculation of Mole Fraction
An aqueous solution of hydrochloric acid contains 36%
HCl by mass. Calculate the mole fraction of HCl in the
solution.
Assume we have 100. g of solution:
Conversion of Concentration Units
Fig 13.19 Calculating molality and molarity
• If we know the density
of the solution, we can
calculate the molality
from the molarity and
vice versa.