Colligative Properties
Objectives: define colligative properties, differentiate between ionic and molecular solutes, and
calculate the change in temperature
Part 1: Definition
define colligative properties- physical properties of a solvent are changed when a
solute is added
Freezing Point is lowered
Boiling Point is raised
Part 2: How much will the BP and FP change?
–ionic solutes (look for criss-cross)
1 molecule of an ionic solute will fall apart into ions
NaCl= 2
CaCl2= 3
Na2SO4= 3
–molecular solutes (compounds that are not formed by criss-cross)
1 molecule of a molecular solute stays as 1 molecule
CH4= 1
The Formula
Part 3: calculate change in temperature
T  m#K 
Steps:
calculate the molality if necessary
determine the number of particles of solute
use the table to determine the K
substitute into the formula and solve
add the change to normal bp or subtract the change from the normal fp
T. O’Toole
Example 1
What is the new boiling point of a solution that contains 40.5 grams of sodium chloride dissolved in 100.0
grams of water.
The normal boiling point of water is 100C, and boiling point is increased. The
new boiling point is 107.1 C.
Example 2
What is the new freezing point of a solution that contains 10.3 grams of CH 3OH dissolved in 100.0 grams of
benzene. The normal freezing point of benzene is 5.46°C.
T. O’Toole
The normal freezing point of benzene is 5.46 C, and freezing point is lowered.
The new freezing point is -11.04 C.
One to GO on…
What is the new freezing point of a solution that contains 27.4 grams of potassium nitrate dissolved in 250.0
grams of water.
The normal freezing point of water is 0 C, and freezing point is lowered. The
new freezing point is -4.02 C.
Minute Paper: Use the Colligative Properties Equation to determine the molality for a
solution of molecular antifreeze required to achieve the new freezing point
T. O’Toole
How do I get from where I am to where I’m going?
10 Minute Makeover
Customize your learning by choosing from the following options each night








Complete the appropriate section on the Portfolio Page
Review the calculation video on the website
Review the PPT file on the website
Read pages 518-525 in the book
Answer questions on page 524 # 33. The answer is in Appendix C.
Check out the tutorial sources in the LiveBinder
Complete the SYS Assignment
Review the skills from today’s Train Your Brain
T. O’Toole