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Concentration
Molality
Molality Defined
 Molality is concentration expressed as
moles of solute per kilogram (mass) of
solvent
 Symbol is m
 Commonly used when studying
concentration when temperature
changes
 Molality does not change with
temperature
Sample problem 13-4
 A solution was prepared by diluting 17.1
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g of sucrose in 125 g of water. What is
the molal concentration of this solution?
Known: 17.1 g C12H22O11 125 g H2O
First find moles!
17.1 g sucrose x 1 mole = 0.049958
342.2872 g
mole
Then 0.049958 mole/0.125 kg =
0.399664 m
Sample problem 13-5
 A solution of iodine in carbon tetrachloride is used when
iodine is needed for certain chemical tests. How much
iodine must be added to prepare a 0.480 m solution of
iodine if 100.0 g of carbon tetrachloride is used?
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Known: 0.480 m I2
100.0 g CCl4
0.480 mole I2 x 0.1000 kg CCl4 = 0.0480
1 kg CCl4
mole I2
0.0480 mole I2 x 253.808 = 12.182784 g
1 mole
I2
Oooh, it’s another problem!
 What volume of 0.245 m sodium chloride
aqueous solution contains 1.0 mole of
this salt?