Wednesday, October 31, 2007
Halloween, Day 2
Happy Halloween! I hope that you have more treats than tricks tonight and that you are able to maintain homeostasis after you eat your candy.Reminder: Extra help in Room 301 tomorrow at about 8AM.
Bio- Posted on Blackboard is the unit objectives/questions review sheet. I will hand out a hard copy of these questions in class, tomorrow but you can get a head-start on the questions, after your festivities.
We reviewed the stages of mitosis and then we focused on, in great detail, what happens to the DNA molecules during the S phase of interphase. We also related DNA replication to the chromosome showing that, when DNA replicates, you STILL have the SAME number of chromosomes but the chromosomes become DOUBLE stranded, made up of identical sister chromatids joined at their centromere.
Eventually, during anaphase of mitosis, the centromeres double and the two sister chromatids are pulled apart by the spindle fibers thus, doubling the number of chromosomes; half of these chromosomes will go to one daughter cell and the other matching half of the chromosomes will go to the other daughter cell so that there is no net gain or loss of DNA/genetic information as the parent cell BECOMES the two daughter cells.
Tomorrow, we will review for Friday's exam. I will again repeatedly show you all how to take a test and I expect EVERY student to follow these always helpful, never harmful test-taking techniques. I also expect to see any students who are not doing well at extra help tomorrow, though all students are welcome, naturally. If you are not doing well, one of the main reasons for your lack of success is your lack of getting any or enough extra help. Given that about 5 students have EVER come to extra help, many of you need to take responsibility for your preparation and performance and learn from your past mistakes. Do not make excuses; get help and get the job done.
If you think that you are fully prepared for a test but are not doing well, show me your answers to all of the unit objective questions BEFORE each test, when I can help you. If they are all correct and detailed responses, it is extremely unlikely (practically impossible) for you to not get a great grade. If your answers are inaccurate and/or sketchy, or not even done, then you have not properly prepared for the test and that will account for your poor performance and lack of understanding. One of your most important jobs as a student is to make sure that you are prepared for each exam.
Chem 7/8- we delved into Graham's (like the crackers) Law, which state the relationship between the relative masses of gas molecules and their respective rates of diffusion and effusion. Graham found that, at the same temperature and pressure, the heavier the gas, the slower its rate of effusion/diffusion and the lighter the gas, the faster its rate of effusion/diffusion.
We explained this phenomenon by looking at the Kelvin Temperature - average kinetic energy connection of Kinetic Molecular Theory. At the same temperature, any two samples of gas molecules will have the SAME average kinetic energy BUT, there are TWO factors that contribute to kinetic energy: velocity AND mass. So, if two molecules have the same KE, the heavier one MUST be going slower (thus diffusing slower) and the lighter one must be going faster (thus diffusing faster). This accounts for Graham's "empirical" (EXPERIMENTALLY found, not just theoretically predicted!) discovery.
We saw how to calculate the relative masses of molecules by using the "atomic mass" numbers listed in the Periodic Table. For example, N= 14.3 atomic mass units and H= 1.0 atomic mass units so, ammonia, NH3 has an atomic mass of 17.3 (one N and three H's). Carbon dioxide, CO2, has an atomic mass of 44.0 atomic mass units
( one C = 12.0 amu's and two O's = 2 x 16.0 amu's) = 44.0 amu ; so, under the same conditions (T and P), ammonia will diffuse/effuse faster than carbon dioxide!
We then did a lab that showed one of the gas laws can be applied in order to crush a can just by condensing the water vapor inside the can. This lab write-up is due Friday.
Chem 9- We focused on Dalton's Laws of Partial Pressures. These two inter-related laws are as follows:
The total pressure of a mixture of gases must be equal to the sum of the partial pressures of the gases in the mixture. That is pretty much an obvious statement but it is essential in understanding the next law: the partial pressure of each gas equals its "mole fraction" times the total pressure. The "mole fraction" of gas "A" represents the fraction of all of the collisions of the gas particles that are due to gas A. Thus, if half of the gas molecules in a mixture of gases are gas A molecules, then gas A molecules cause half of the collisions that are occurring at any given time in that container. Therefore, gas A causes/accounts for half of the pressure in that mixture.
We then did several examples and permutations of Dalton's Law problems.
# posted by C @ 1:12 PM 
