Friday, November 2, 2007
Fri-Day 2
Reminder for Chem Classes!
The Gas Law Unit Exam has been moved to next THURSDAY (11/08), due to the shortened periods on Wednesday. Furthermore, the first quarterly exam will be given the following Tuesday and Wednesday (11/13 and 11/14, we are off for Veterans Day that Monday).
Bio- we had our unit test today. On Monday, we begin our new unit, which focuses on the other MAJOR feature of DNA: its ability to also act as a TEMPLATE for the synthesis of RNA ( "transcription", which is then used as a template for the production of proteins ("translation") which give an organism its specific traits! Basically, we'll see how particular DNA sequences (genes or "alleles") eventually get translated into specific traits such as eye color, hair color, metabolic rate, etc.
This is the MOST important unit in understanding Biology/Life at the molecular level.
If you have time, you can get a head start on the upcoming outline homework:
on Monday, you'll be assigned text section 11.2; on Wednesday, you'll be assigned section 11.3.
Chem 7/8- we did another gas density at STP problem; the key to these problems is getting the mass and volume of the particular substance. That is why we take ONE MOLE of the gas because one mole of ANY gas at STP (only!) occupies 22.4 liters of space. Then we just have to get the mass of one mole of the substance (the MOLAR MASS), which we get by adding up the atomic masses (in grams) of each atom in the formula (e.g. N2O5 has a molar mass of :
[(2 x 14. g) + (5 x 16. g)] = 108 grams; therefore, its density at STP is 108 grams divided by 22.4 liters, which is 4.82 grams per liter.
We then did our Charles's Law lab as we saw that, at constant pressure and moles of gas (a mixture of nitrogen and oxygen, in this case), as temperature decreases, the volume of the gases decreases.
We will discuss that lab and it will be due next Wednesday. Also, I found the graded Kinetics Labs in our classroom today; they were in my ditto drawer; I'll return them to you on Monday.
We then finished by explaining that real gases become more "ideal" (i.e. follow the gas laws more accurately) when they are under conditions that make the gas match the tenets of Kinetic-Molecular Theory: that their individual volumes become negligible AND that the molecules have totally overcome their attractions for each other. Thus, real gases follow the gas laws quite well when the gases are at HIGH TEMPERATURE (so the molecules can easily overcome their attractions by flying by each other so fast) and LOW PRESSURE (so there is lots of "space between" the molecules thus making each molecule's volume insignificant).
Just remember, a real gas STAYS in the GAS phase at HIGH temperatures and LOW pressures!
Chem 9- we didn't get to discuss any questions that you may have about the crushed can lab, today, so I will discuss BOTH the crushed can lab and the Charles's law lab on Monday; bring both labs in and we will go over them completely. Those labs will be due on Wednesday.
We did discuss an implication of Avogadro's Law: equal volumes of any gas at the same temperature and pressure MUST contain an equal number of molecules in that volume (it does NOT matter that one type of molecule is bigger/larger than another!!!).
One thing that has been experimentally determined and related to Avogadro's Law is that ONE MOLE of any ("ideal" - follows the gas laws and tenets of K-M Theory) gas at STP takes up 22.4 L of space. So if you have, 22.4 L of oxygen or ozone or nitrogen or carbon monoxide or carbon dioxide gas at STP, there ARE 6.02 x 10^23 molecules of any of those gases in that 22.4 L volume container.
Using our reference tables, we are fortunate that we can just look at the "atomic mass" of ANY element and know that the number seen is the MASS of that element IN GRAMS for one mole of atoms of that element, e.g. one mole of Argon atoms has a mass of 39.948 grams, whereas one mole of Neon atoms has a mass of 20.179 grams. Thus each Neon atom weighs about half as much as each Argon atom.
From this, we began to do some gas density calculations ONLY for gases at STP (1 mol of ANY gas at STP has a volume of 22.4 L)!!!
The Gas Law Unit Exam has been moved to next THURSDAY (11/08), due to the shortened periods on Wednesday. Furthermore, the first quarterly exam will be given the following Tuesday and Wednesday (11/13 and 11/14, we are off for Veterans Day that Monday).
Bio- we had our unit test today. On Monday, we begin our new unit, which focuses on the other MAJOR feature of DNA: its ability to also act as a TEMPLATE for the synthesis of RNA ( "transcription", which is then used as a template for the production of proteins ("translation") which give an organism its specific traits! Basically, we'll see how particular DNA sequences (genes or "alleles") eventually get translated into specific traits such as eye color, hair color, metabolic rate, etc.
This is the MOST important unit in understanding Biology/Life at the molecular level.
If you have time, you can get a head start on the upcoming outline homework:
on Monday, you'll be assigned text section 11.2; on Wednesday, you'll be assigned section 11.3.
Chem 7/8- we did another gas density at STP problem; the key to these problems is getting the mass and volume of the particular substance. That is why we take ONE MOLE of the gas because one mole of ANY gas at STP (only!) occupies 22.4 liters of space. Then we just have to get the mass of one mole of the substance (the MOLAR MASS), which we get by adding up the atomic masses (in grams) of each atom in the formula (e.g. N2O5 has a molar mass of :
[(2 x 14. g) + (5 x 16. g)] = 108 grams; therefore, its density at STP is 108 grams divided by 22.4 liters, which is 4.82 grams per liter.
We then did our Charles's Law lab as we saw that, at constant pressure and moles of gas (a mixture of nitrogen and oxygen, in this case), as temperature decreases, the volume of the gases decreases.
We will discuss that lab and it will be due next Wednesday. Also, I found the graded Kinetics Labs in our classroom today; they were in my ditto drawer; I'll return them to you on Monday.
We then finished by explaining that real gases become more "ideal" (i.e. follow the gas laws more accurately) when they are under conditions that make the gas match the tenets of Kinetic-Molecular Theory: that their individual volumes become negligible AND that the molecules have totally overcome their attractions for each other. Thus, real gases follow the gas laws quite well when the gases are at HIGH TEMPERATURE (so the molecules can easily overcome their attractions by flying by each other so fast) and LOW PRESSURE (so there is lots of "space between" the molecules thus making each molecule's volume insignificant).
Just remember, a real gas STAYS in the GAS phase at HIGH temperatures and LOW pressures!
Chem 9- we didn't get to discuss any questions that you may have about the crushed can lab, today, so I will discuss BOTH the crushed can lab and the Charles's law lab on Monday; bring both labs in and we will go over them completely. Those labs will be due on Wednesday.
We did discuss an implication of Avogadro's Law: equal volumes of any gas at the same temperature and pressure MUST contain an equal number of molecules in that volume (it does NOT matter that one type of molecule is bigger/larger than another!!!).
One thing that has been experimentally determined and related to Avogadro's Law is that ONE MOLE of any ("ideal" - follows the gas laws and tenets of K-M Theory) gas at STP takes up 22.4 L of space. So if you have, 22.4 L of oxygen or ozone or nitrogen or carbon monoxide or carbon dioxide gas at STP, there ARE 6.02 x 10^23 molecules of any of those gases in that 22.4 L volume container.
Using our reference tables, we are fortunate that we can just look at the "atomic mass" of ANY element and know that the number seen is the MASS of that element IN GRAMS for one mole of atoms of that element, e.g. one mole of Argon atoms has a mass of 39.948 grams, whereas one mole of Neon atoms has a mass of 20.179 grams. Thus each Neon atom weighs about half as much as each Argon atom.
From this, we began to do some gas density calculations ONLY for gases at STP (1 mol of ANY gas at STP has a volume of 22.4 L)!!!
# posted by C @ 11:41 AM 
