1. Colligative properties
Solutions Part 4

2. Electrolytes: a quick review
Electrolytes form ions in solution.
Ions allow water to conduct electric current
Three types of electrolytes: strong , weak, and non-electrolytes.

3. Strong Electrolytes Strong electrolytes ionize completely in water.
More ions in the water, more conductivity.
Strong electrolytes include:
Strong acids HCl H+ + Cl-
Strong bases NaOH Na+ + OH-
Soluble salts CaCl2 Ca2+ + 2Cl-

4. Molarity:review Moles per liter
1.0 M = 1 mole solute per 1 liter solution.
Question
What is the molarity of 1.56 g of gaseous HCl in a 26.8 mL solution?

5. Mole Fraction
mole fraction: the number of moles of a component of a solution divided by the total number of moles of all components.

6. Example: 58.5 grams of NaCl are in a one liter solution.
What is the Molarity of the NaCl?
1 M
58.5 grams of NaCl are in 1800 grams of water.
What is the mole fraction of NaCl?
1/101

7. Molality
Definition: a unit of concentration, defined to be equal to the number of moles of solute divided by the number of kilograms of solvent .
This is not to be confused with Molarity

8. Why so you add salt to an icy sidewalk?
It melts the ice.
How?
Colligative properties.
Why so some types of salt seem to work better than melting the ice than others.
Why?

9. Colligative properties
are properties of solutions that depend on the number of molecules in a given volume of solvent and not on the properties (e.g. size or mass) of the molecules.[1] Colligative properties include: lowering of vapor pressure; elevation of boiling point; depression of freezing point and osmotic pressure.

10. Colligative properties
How many ions are formed from the dissociation of 1mole of NaCl?
From CaCl2?
From NH4Cl
From H3PO4?

11. Question
What is the concentration of each type of ion in the following solutions?
0.50M Co(NO3)2
1 M Fe(ClO4)3

12. Answer Co 2+ 0.5 M NO3 - 1.0 M Fe 3+ 1 M ClO4 - 3M
Why isn’t it 3M Cl- and 12 M O2- ??

14. Vapor Pressure Reduction
The particle act to attract the water molecules making it more difficult for them to free themselves to become vapor.

15. Freezing point depression
The individual particles interfere with the water’s ability to form a crystal depressing the freezing point.