1. Solutions and Their Properties
Chapter 13

2. Learning Objectives Students understand
The energetics of the solution process
The basis of the “like dissolves like” rule
How changes in pressure and temperature affect solubility

3. Learning Objectives Students will be able to
Use the units of solution concentration
Calculate the enthalpy of a solution
Use Henry’s law
Use Le Chatelier’s principle

4. Solutions and Their Properties
A solution is a homogenous mixture of two or more substances in a single phase.
solute vs. solvent
The changes that occur when a substance is dissolved in a pure liquid are called colligative properties.

5. 13.1 Units of Concentration
Molarity (mole solute/liter solution) does not work when dealing with colligative properties
solute molecules take up some volume
Four units that can be used to calculate concentration of solute per solvent are…
molality, mole fraction, weight percent, parts per million

6. Mole Fraction
The mole fraction, X, of a solution is defined as the amount of a given component of a mixture divided by the total amount of all the components of the mixture.
XA = nA / (nA + nB +…)

7. Practice Problem
If you dissolved 10.0 g of sugar, C12H22O11 in 250. g of water, what is the mole fraction, molality, and weight percent of sugar?

8. 13.2 Solution Process Unsaturated Saturated Supersaturated
Solubility is the concentration of solute in equilibrium with undissolved solute in a saturated solution.

9. Liquids Dissolving in Liquids
If two liquids mix to form a solution, they are miscible. Immiscible liquids do not mix and exist as separate layers.
Like dissolves like!

10. Solids Dissolving in Liquids
Once an ion has entered a solution and is surrounded by water molecules, then they are hydrated.
Heat of solution may be endothermic or exothermic depending upon how much energy is absorbed or lost by the reaction.

11. Enthalpy of Solution
Heat of solution can be calculated by taking the sum of the standard heat of formation of the products minus the sum of the heat of formation of the reactions.

12. Practice Problem
Use the data in Table 13.1 (p. 478) to calculated the enthalpy of solution for NaOH.

13. Homework
After reading sections , you should be able to do the following…
P. 505 (1-21 odd)

14. 13.3 Factors Affecting Solubility
Solubility of a gas in a liquid is directly proportional to the gas pressure.
Sg = kHPg
where S is the gas solubility, P is the partial pressure of the gaseous solute, and k is the Henry’s Law constant
carbonated soft drinks; SCUBA tanks (narcosis and the bends)

15. Henry’s Law
What is the concentration of CO2 in water at 25oC when the partial pressure is 0.33 bar?

16. Temperature Effects
Solubility of solids in water increases with increasing temperature
Solubility of gases in water decreases with increasing temperature
Fish seek lower depths in summer
Thermal pollution

17. Practice Problem
Case Study p. 482 – Henry’s Law and Exploding Lakes

18. Le Chatelier’s Principle
States that a change in any of the factors determining an equilibrium causes the system to adjust by shifting in the direction that reduces or counteracts the effect of the change
gas + liquid solvent  saturated solution + energy

19. Temperature Effects Le Chatelier’s Principle
States that a change in any of the factors determining an equilibrium causes the system to adjust to reduce or counteract the effect of the change.
Gas + liquid solvent  saturated solution + heat
increasing temperature shifts reaction left

20. 13.5 Colloids
Colloids are intermediate between a solution and a suspension. (Jello, milk, fog)
Tyndall effect: colloids scatter visible light when dispersed in a solvent, making the mixture appear cloudy

22. Colloids Hydrophilic and hydrophobic
Emulsions are colloidal dispersions of liquid in liquid (mayo, milk)
emulsifying agents keep colloids from settling out

23. Surfactants Soaps and detergents are emulsifiers.
These substances affect the properties of surfaces are called surfactants; ones used for cleaning are called detergents.

24. Homework
After reading Section , you should be able to do the following…
P. (19-24, 51-52)