This document discusses freezing point depression and colligative properties. It defines key terms like molality, freezing point depression constant, and Van't Hoff factor. The goals are to determine the freezing point depression constant of water, examine the relationship between concentration and freezing point, and explore the effect of electrolytes. Students will prepare sugar solutions of varying concentration and one salt solution to compare the freezing point depression.

1. Freezing Point Depression
General Chemistry Laboratory

2. Goals
• To determine the freezing point depression
constant of water
• To determine the relationship between
concentration and freezing point
• To explore the effect of electrolytes on the
freezing point of a solution

3. Colligative Properties
• Properties that depend on the number of
dissolved particles (aka concentration)
present in the solution
• What is the effect of increased
concentration on BP and FP?

4. Molality (m)
𝑚 =
moles of solute
kg of solvent
Example: What is the molality (MW = 180.16
g/mol) of a glucose solution containing 50 g
glucose in 100 mL of water?

5. Freezing Point Depression
Relationship between freezing point and
molality:
ΔT = iKfm
ΔT: Change in temperature from the pure
solvent’s original freezing point
i: Van’t Hoff Factor
Kf: Freezing Point Depression Constant

6. Van’t Hoff Factor (i)
• The ratio of solute particles to the number
of the formula units dissolved
𝑖 =
𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠 𝑖𝑛 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑓𝑜𝑟𝑚𝑢𝑙𝑎 𝑢𝑛𝑖𝑡𝑠 𝑑𝑖𝑠𝑠𝑜𝑙𝑣𝑒𝑑
• Electrolyes break up into ions in solution
• Nonelectrolytes do not yield ions when
dissolved

7. Example
– Glucose, C6H12O6
– Magnesium chloride, MgCl2

8. Procedural Hints
• Sucrose is very soluble in water, approx. 2
g/mL
• Prepare at least 4 sugar solutions of varying
concentration (max conc. <0.5 g/mL)
• Solutions should be between 100 and 200 mL
• One salt solution should be prepared with
equal molality to one of the sugar solutions

9. Interpreting Your Data
• Interpreting these graphs will be on your exams.

10. Waste Disposal
• Solids  trash can
• Liquids  sink
• Dry ice  sink
• Brush off the balances when you are done
weighing your sample.
• Weigh boats should be put in the trash
after use.