Monday, October 20, 2008
Mon-Day 1
AP Chem- we labelled/named some of the reactions that we had balanced: double replacement with precipitation, acid-base neutralization, etc.
We saw that, when a redox reaction occurs (especially in aqueous solutions), simple mass balancing of reactants and products is inadequate to obey the Law of Conservation of Charge.
We then developed the "Half-Reaction" method for balancing a redox reaction; last year, you learned the "oxidation number" method for balancing a redox reaction. The "half-reaction" method is easier in that it avoids the use of an arbitrary oxidation number system and deals solely with masses and charges.
We practiced a few examples, two redox reactions in acidic solutions (excess H+) and one in basic solution (excess OH- ... TWO MORE STEPS).
We then introduced the concept of "limiting" reactants and "excess" reactants in stoichiometry.
With a balanced equation and known quantities of reactants, you can determine which of the reactants LIMITS the number of moles of product(s) formed.
We discussed our hydrate lab and came up with two plausible UNAVOIDABLE experimental sources of "error"/uncertainty.
For excess water loss from the hydrate, if some minor anhydrous salt sublimation occurred (unbeknownst to you of course, you CANNOT see this occurring!), the mass lost would be recorded as water mass lost, thus increasing the perceived percent water in the original hydrate.
If the anhydrous salt somewhat rehydrated from moisture in the air (during cooling...again, you cannot see this occurring), the mass lost would be LESS than it would have been if NO water remained, thus decreasing the perceived percent water in the original hydrate.
Your job in the writeup is to plug in data that is consistent with each of these two scenarios and show your calculation for the percent water (as instructed). I do not care what the numbers are as long as they are consistent with the scenario and with you original hydrate mass.
Bio 6/7- we began our new unit on mitosis/cell division/DNA by discussing the reason/necessity for cell division. We focused on the increase in both surface area and volume as a cell grows. However, for any growing cell, the volume increases faster than the surface area so the cell must divide or die due to the lack of timely diffusion of nutrients to their required locations in the cell.
We went through the phases of mitosis with cytokinesis, including the "rest phase", interphase, during which the cell and its parts grow and during which the DNA replicates itself.
We began the state lab on diffusion in an onion cell.
Bio 8- we began our new unit on mitosis/cell division/DNA by discussing the reason/necessity for cell division. We focused on the increase in both surface area and volume as a cell grows. However, for any growing cell, the volume increases faster than the surface area so the cell must divide or die due to the lack of timely diffusion of nutrients to their required locations in the cell.
We saw that, when a redox reaction occurs (especially in aqueous solutions), simple mass balancing of reactants and products is inadequate to obey the Law of Conservation of Charge.
We then developed the "Half-Reaction" method for balancing a redox reaction; last year, you learned the "oxidation number" method for balancing a redox reaction. The "half-reaction" method is easier in that it avoids the use of an arbitrary oxidation number system and deals solely with masses and charges.
We practiced a few examples, two redox reactions in acidic solutions (excess H+) and one in basic solution (excess OH- ... TWO MORE STEPS).
We then introduced the concept of "limiting" reactants and "excess" reactants in stoichiometry.
With a balanced equation and known quantities of reactants, you can determine which of the reactants LIMITS the number of moles of product(s) formed.
We discussed our hydrate lab and came up with two plausible UNAVOIDABLE experimental sources of "error"/uncertainty.
For excess water loss from the hydrate, if some minor anhydrous salt sublimation occurred (unbeknownst to you of course, you CANNOT see this occurring!), the mass lost would be recorded as water mass lost, thus increasing the perceived percent water in the original hydrate.
If the anhydrous salt somewhat rehydrated from moisture in the air (during cooling...again, you cannot see this occurring), the mass lost would be LESS than it would have been if NO water remained, thus decreasing the perceived percent water in the original hydrate.
Your job in the writeup is to plug in data that is consistent with each of these two scenarios and show your calculation for the percent water (as instructed). I do not care what the numbers are as long as they are consistent with the scenario and with you original hydrate mass.
Bio 6/7- we began our new unit on mitosis/cell division/DNA by discussing the reason/necessity for cell division. We focused on the increase in both surface area and volume as a cell grows. However, for any growing cell, the volume increases faster than the surface area so the cell must divide or die due to the lack of timely diffusion of nutrients to their required locations in the cell.
We went through the phases of mitosis with cytokinesis, including the "rest phase", interphase, during which the cell and its parts grow and during which the DNA replicates itself.
We began the state lab on diffusion in an onion cell.
Bio 8- we began our new unit on mitosis/cell division/DNA by discussing the reason/necessity for cell division. We focused on the increase in both surface area and volume as a cell grows. However, for any growing cell, the volume increases faster than the surface area so the cell must divide or die due to the lack of timely diffusion of nutrients to their required locations in the cell.
# posted by C @ 11:12 AM 
