Tuesday, March 22

Mr. Henderson started today's day with an argument with himself. He had two voices, one on each shoulder, arguing if the WebAssign due tomorrow should be pushed back to Thursday. He ended up postponing the WebAssign and offered extra credit points to whoever did it by tomorrow at 8 A.M.

We started the bulk of the class period practicing problems on page 7 and 8. These problems were about solution stoichiometry. The answers that we did were:

3a) 0.0182 grams

3b) 0.123 liters

5a) Na2CrO4 + Pb(NO3)2 ---> 2 NaNO3 + PbCrO4

5b) 13.3 grams PbCrO4

These problems consisted of the same concept as did the old stoichiometry problems (mole island). The only major difference was that we had to use a molarity ratio (for example #5b of .4100 M). This means that there are .4100 moles in every 1 liter.

The rest of the class period was dedicated to colligative properties. The four colligative properties are vapor pressure lowering, boiling point elevation, freezing point lowering, and osmotic pressure. Mr. Henderson then explained how this was relevant in every day life. He stated that we add salt to the roads when it snows because it is a colligative property. This means that it lowers the freezing point of water. By doing this it is less likely for the water from the snow to freeze on the roads. This makes driving a lot safer. Hooray for colligative properties! How much lower the freezing point of water gets is only dependent on the solvent and amount of solute.

We concluded class by performing math problems on this idea. The formula for boiling point elevation equaled (i)(m)(Kb). i is the number of particles per solute, m is the molality, and Kb is the boiling point elevation constant which depends on the solute. i would equal 2 for NaCl, 3 for CaCl2, and 4 for FeCl3 because if these molecules were broken down there would be that many individual particles. The equation for the freezing point depression is the same other than the fact that the Kb turns into a Kf which is a constant as well. We put these formulas to the test and did numbers 7 and 8 on page 17. The answers are:

7) 0.65 degrees Celsius

8) 2.90 degrees Celsius

Homework is to get started on the 2 WebAssigns due Thursday.