CEM Exam 4

I just wanted to clarify the final set of questions.

#36  The decomposition of silver chloride.  This is exactly like the problems in class.  You get the balanced equation (2AgCl –> 2 Ag + Cl2) which allows you to relate the unknown (moles of chlorine gas) to the moles of known (silver chloride).  Moles of silver chloride is determined by molar mass from the mass given.  Volume of gas is determined from the moles of chlorine gas and the ideal gas equation.

#37  Again a simple input out put problem.  The idea was a double displacement equation that produced lead (II) chloride as the insoluble product (the other option was ammonium nitrate and that is definitely soluble).  Then you use molarity to find the limiting reagent between the two inputs, followed by stoichiometry, then molar mass to get grams.

#38.  The water vessel question.  There are two ways to solve this question (which was in the practice problems).  The first way was to solve it using the idea of partial pressures and solving for the number of moles, then back calculating the volume using the ideal gas law.  This is the way I used in the answer key and it works just fine.  However, there is a much more simple solution.  The system has a constant volume and temperature, the only thing that affects the pressure is the number of particles in the system.  As Avagadro showed us, the nature of particles is irrelevant when observed in mass, just the number.  In absolute terms the final state of the system has two-thirds the number of particles as the initial state.  Since all gases are ideal in the system and ideal means there are linear relationships between the gas properties you can find the final pressure by multiplying the initial pressure (1.5 atm) by 2/3 (ratio of final to initial) to get a final pressure of 1.00 atm.

#39  This relates back to Avagadro’s Hypothesis (#13 on the exam) and the idea of what an ideal gas means.  The answer is it is irrelevant whether it is butane, xenon, or any other ideal gas, given a system with the same conditions all ideal gases have the same volume.  I’ll give you partial credit if you picked one and gave me some decent justification for your wrong answer.

Office Door Etiquette

You would be surprised how hard it is for people to understand when a professor is and isn’t available.  This is not meant to be snide, but just because I am heading to my office (or that general direction) doesn’t mean I have that extra twenty minutes you desperately need.  There are days when I might only have thirty minutes in the middle of the day to go to the bathroom, scarf down a protein bar, and exchange materials for different classes or labs.

One of the biggest problems is when I am in my office, so here is a handy reminder for basic rules.

Door completely closed (even if I just stepped in) – I’m busy, it might be that I am just grabbing something between classes/meetings/labs/etc. or that I have to make a call at that point.  I’m not ignoring you, but other priorities are taking precedent at that moment.

Door cracked open – I’m in my office and can be interrupted but am currently doing something, please politely knock and wait for me to respond.

Door wide open – I’m in my office and open to assist you, just come on in and we can have a sit down.

Grades for BIO220

Yes, there was a problem with the E2 column in the last grade sheet, as a number of you informed me (interestingly only those of you whose grade was worse than you had).  I looked at it and there was an error in the printed spreadsheet (PDF), which is derived from my original copy, but reordered for grade privacy.  I’ve fixed the error and posted a new version with the correct E2 grades.  Before you say, how do you know that was my E2 grades, I went back to the hardcopy of postE2 to double check (+2 for the error on the scantron).  If it is wrong you need to bring your test to me to show it (that is why you get them back).

New Post E3 grades

Molar Mass of Butane Lab

I had to figure out how to evaluate the answers you gave on the Molar Mass of Butane lab and decided on the following criteria based on your deviation from the accepted value (~54 g/mol).

  • +/- 30.0% or less = 10/10
  • +/- 30.1-40.0% = 8/10
  • +/- greater than 40% = 6/10

These are fairly generous error ranges and reflect the precision with which you accomplished the task.  The majority of groups are in the 8 or 10 range, though there are a number of 6.  For reference the best estimate in the morning lab was 50 g/mol and the best in the afternoon was 52 g/mol, so it was doable.

Assignment 2 for BIO220 Talks

Assignment 2 for your talks will be due on Monday November 24, 2014.  The work may be submitted electronically or on paper, but is due by Monday.  I WILL NOT accept late work.

Assignment 2 (from syllabus)

The second assignment has two parts, both must be typed. The first part is to outline the taxonomic classification of your microbe from Domain (in the case of all nonviral microbes) or Order (for viruses) down to species level. Not all taxonomic ranks will be used by each microbe, so research the answer. The second part is a one paragraph synopsis of your organism covering what it is, what it causes or does, and where is can be found? The total assignment is worth twenty (20) points, and new references do not need to be included.

BIO220 Grades Post E3

The exams for BIO220 are graded.  There was no curve since the median was a 75% and the high score was a 92%.  The overall grades are calculated with the most current lab grades I have, which are a couple of weeks old.

Grades for CEM131

The new grade sheets are posted for both sections of CEM131.  Of note, neither section needed a curve because the median was high enough.  The top score in the morning section was a 98% and the afternoon was a 96%.

I need to mention one thing I observed during testing.  I noticed a few individuals during each section check their phones during the exams for various number of lengths of time.  I am willing to give you the benefit of the doubt this one time.  However, ANY PHONE USE DURING FUTURE EXAMS WILL RESULT IN AN AUTOMATIC SCORE OF ZERO (0) THAT CANNOT BE DROPPED.  I hope that is clear enough for you since a number of you seemed to have either forgotten this or are taking advantage of my good nature.  In the future it won’t be a question of what you are doing on the phone, it will be taken as cheating, NO MATTER THE USE.

Class cancelled today 11/4/14

I had a minor car issue this morning and blew out two of four tires. It is going to take a while to get the repaired and I’ll have to keep the classes on the same schedule, so I need to postpone the test till Thursday for both classes. We will figure out lab later.

No lab today either.

Test WILL be on Thursday.