# Recently in *Fall 2010* Category

Hello -

Since Expt. 9 was shortened there is not much to talk about. Make sure your students use the disposable test tubes the stockroom put out instead of their own for Part A, since it's almost impossible for the students to clean the test tubes afterward. Also, remind your students to not make the poly(ethylene oxide) gel. Make one demo beaker of the gel and pass it around to all the students in the lab.

Also remind them to not burn the plastic on the clamps...

Try to stagger what part your students start on, since the lines for the density part of the experiment were long towards the end.

This lab goes quickly, especially since they don't do a lot of the questions.

Nina

Hello -

The Monday TAs decided to let the students take their lab reports home and turn them in next week.

I set up one of the apparatus for Part I so that the students could see what it looked like. I let the students set up the other ones. Remind them that the value for d they should use is on page 6-3 directly above the table.

Check all students' voltages early on. It is critical to have good voltage numbers and it is easy for the students to screw up. Red should be the lowest voltage and green the highest voltage.

Point out the sample calculations on page 6-6 and 6-7, for some reason the students don't know it's there. Also, there is a typo on page 6-11, in step 6 it says to use Table 6-1, it should read Table 6-2. Figure 6-3 confuses them a lot, so you will need to explain it several times.

Nina

Hello,

Part two of the experiment went very smoothly for the students. I mostly had to answer questions about how to use excel. Nearly everyone was done by 3:15pm, so time is not a problem with this lab. Nothing really caused problems for the students.

Nina

Hello all,

There were some minor problems with the lab. Remind students how to print their graphs (ie: be connected to the internet) and that they do need to print out 3 graphs. Also, many students when graphing absorbance versus concentration somehow got the x-axis in the wrong magnitude. Their calculations were correct, but the way they entered the concentration into Excel made Excel do something weird (it reads 1E-5 as 1). Make sure their slope is in the tens of thousands not 0.1.

The equipment worked well, as did all the solutions.

Nina

Yes, the students definitely lose sight of the goal of this lab during the calculations. Actually obtaining the data was not difficult for most students and no one was struggling for time on data collection.

Many students were confused that "heat of" means q, and frequently forgot that q has units of joules. Also, make sure to check their calorimeter constant, since many first tries result in negative values, or they forget to divide q(cal) by delta T. They usually have a math error, not a procedural error.

For Part A, remind them to look at the big box on page 5-7, and if needed remind them of the relationship between density/volume/mass.

For Part B, if you tell your students to use the oven, be wary that the temperature of the Al will decrease if students are constantly opening/closing the door. This will muck up their Ccal if you wrote what the temperature is supposed to be (85) on the board.

For Part C, many students did not know where to start for the calculations, I pointed them in the direction of Eq. 5 on page 5-9 and that seemed to help.

One student finished the entire lab report, the rest took it home with them.

Nina

Hello -

For Experiment Three, the two biggest problems were calculating theoretical yield and time management. Student who were comfortable with the calculations easily completed the experiment while those not comfortable were pressed for time. I had put a sample theoretical yield calculation on the board as part of my pre-lab, but ~20% of my students still struggled.

Remind them to save their filtrate from each trial and that the lab continues on page 3-6. Also mention the location of the chemicals, they seemed to have a hard time finding them for whatever reason.

Otherwise it went smoothly with few equipment/reagent problems.

Nina

**Experiment 2 Part 1**

Experiment 2 Part 1 went smoothly for the Monday afternoon lab. There was some confusion on which waste container the Experiment 2 waste belongs in, despite the lab manual's clear instructions. Make sure the students know to not put their waste in the Expt. 1 Ag+ container.

A common mistake was that students were putting NaCl(s) as a product. Some also struggled with knowing what the products were. The only solution to that is a series of leading questions and discuss the reactions more generally (ie: strong acid-strong base always forms salt and water, etc.).

Also emphasize 2Cl- versus Cl2 and so forth. This still trips up many students.

Nina

**Experiment 2 Part 2**

Experiment 2 Part 2 was relatively easy for the students. Most finished after 2 hours, but I did have a few slower paced students who took the entire lab period.

For Part E some students tried to add water as a reagent... obviously this only confused them further. So keep an eye out for that one.

In part G the lab manual asks the students to rinse and save the copper wire for Part J. This is a typo and should be for Part I.

Question 4 stumped many of my students until I reminded them that reducing agents have different strengths and that a strong reducing agent is a weak oxidizing agent.

Nina

**Experiment 1 Parts I and II**

First, I would like to apologize to all of the Tuesday TAs, since as the Monday Forum TA I was supposed to have this done last night. It won't happen again.

Experiment 1, Parts I & II didn't seem to be conceptually difficult for the students. Since Monday had both check-in and the experiment to do, I gave an abbreviated pre-lab that discussed only how to use glassware/balances/conductivity probe, etc. This seemed to be helpful for them.

Some students struggled with the multiple dilutions in Part II, however I received fewer questions on this than in previous semesters.

Sometimes the computer will lose the connection to the conductivity probe. This causes the green collect button to become gray and not collect data when pressed. To fix this, have your students reopen the calibration file in Logger Pro (see paragraph 5 of Appendix F). Also check that there isn't a faulty connection in the USB/Go Link/Probe wiring.

Nina

**Expt 1 Part III**

Part III went much more smoothly than Parts I and II. All students completed everything for Part III, so time should not be an issue.

The biggest problem I had in my lab section was Q16. I would say 75% of my students had no clue where to start on this one. In my pre-lab talk I had briefly touched on precipitation reaction/titration/equivalence point, but it obviously didn't help. Almost all of the students also used M1V1=M2V2 for Q12, which is also incorrect. I ended up demonstrating how to do Q12 (without actually plugging numbers in) in order to teach them about Q16.

Lab equipment wasn't an issue. I showed each lab pair how to use a buret and explained how to find the total volume. Also remind them to use the volumetric to make the stock NaCl solution, a surprising number forgot about that in a week.

Nina