Mini-Unit: Colligative Properties

1
Mini-Unit Colligative Properties
Day 1 - Notes

• Introduction and Molality

2
After today you will be able to

• Explain what a colligative property is
• Perform calculations using the molality (m)
  formula

3
Colligative Properties

• A property of a solution that depends only upon
  the number of solute particles, and not upon
  their identity.
• Depends only on the solute concentration.
• Molality (m) Another way chemists express the
  concentration of a solution, in moles per kg.

4
Molality
moles of solute
kg of solvent
5
Example

• What is the molality of a solution that contains
  65.3g of Na2S in 1500g of solvent (H2O)?
• m
• mol
• kg

?
1 mol Na2S
65.3gNa2S
x

0.837mol Na2S
78.05gNa2S
1kg
1500g
x
1.5kg

1000g
0.837mol Na2S
0.56 mol/kg

1.5kg
6
Example

• How many kg of H2O would contain 42g of K3P in a
  0.885m solution of K3P?
• m
• mol
• kg

0.885m
1 mol K3P
42gK3P
x

0.28 mol K3P
148.27gK3P
?
0.28 mol K3P
0.32kg
0.885m


x
7
Questions?Complete WS1