CHEM 1411 - General Chemistry I
Course (Lecture and Lab) Syllabus
Summer 2007
Instructor: Dr. Shawn Amorde
e-mail address: samorde@austincc.edu
web page: http://www.austincc.edu/samorde
Office Hours: TThF, 7-8am
Solutions
Text Chapters (14.1-14.8, 14.10-14.12, 14.15, 14.18)
Recommended Problems (4, 8, 10, 12, 13, 14, 16, 22, 26, 28, 32, 94, 96)
Dissolution
1. Dissolution Process
2. Solids in Liquids
3. Liquids in Liquids
4. Gases in Liquids
5. Rates of Dissolution and Saturation
6. Temperature and Solubility
7. Pressure and Solubility
8. Molality
Colligative Properties
9. Fractional Distillation
10. Boiling Point and Freezing Point Deviations
11. Osmosis
12. Colloids
13. Hydrophilic and Hydrophobic
Dissolution (Dissolving)
A solution is a homogeneous mixture, in which settling does not occur. The solvent is the medium in which solutes are dissolved. The solvent is usually the most abundant!! In our bodies, water is the solvent!! There are some major factors which govern solubility. We will look at these in this chapter.
A substance may be dissolved in a solvent with or without a chemical reaction. For example, sugar is soluble in water, but does not react with water. Aluminum foil is soluble in sulfuric acid, but only through a chemical reaction. The trick to determining whether a reaction has taken place is to evaporate the water and see what is left!!
We must keep in mind two factors when dissolving, first; the process is favored if the solution has less energy than the solvent and solute, this is called an exothermic process and second; if the “randomness” of the solution is increased this process is favored.
If a solution gets hot when you mix it, the process is exothermic and the heat of solution can be measured. If the heat of solution is negative, the dissolution releases heat.
Remember these factors;
The dissolution process results in both solvent and solute molecules separating from each other!! This is favorable if the new interactions between solvent and solute are strong and favorable!!
Solids Dissolving in
Liquids
The first property of solids to consider is the crystal lattice energy.
Energy is required to “break up” the crystal lattice. Energy is also required to “break up” the intermolecular forces between solvent molecules. Finally, energy may be gained from the intermolecular forces of the solvent interacting with the solute. This is called salvation or for water hydration.
Let’s look at some specific examples.
Liquids Dissolving
Liquids
The ability of one liquid to dissolve another is called miscibility. Let’s compare forces for polar and nonpolar liquids so we can understand why some liquids are miscible and some are immiscible.
Gases in Liquids
The dissolving of gasses in liquids often occurs with chemical reactions or ionization. For example, the polar covalent acids like HF, and HCl. These acids gain hydrogen bonding forces when dissolved in water, thus the driving force behind dissolution.
Rates of Dissolution
and Saturation
There are two competing forces in solutions of solids in liquids.
At some point you reach saturation, where you can not get anymore solid to dissolve. At this saturation point no more molecules will be dissolved unless dissolved molecules reform crystals. Although, if you increase the temperature you can dissolve more solute!! This is called a supersaturated solution. As the solution cools re-crystallization often occurs.
Temperature can have a large effect, but pressure does not for liquids and solids. Dissolving gases however is pressure dependant. There is another Gas Law here;
Henry’s Law, which states that the solubility of a gas in a liquid at any given temperature is directly proportional to the partial pressure of the gas over the liquid.
Remember the CO2 in
Molality
The molality of a solute in solution is the number of moles of solute per kilogram solvent.
What is you have a mixture of solutes? You would use a mole fraction.