April 2011 Archives

Experiment 16 (Part 2)

Hi everyone,

This would probably be my last post for this semester! It is nearly over :)

So this lab is quite a long one since they have to hand in their reports at the end of the lab again.

Here are the tips of the week:

  • Remind them to change their salt bridges when they get dry. Specially if they are getting weird numbers it sometimes helps
  • Double check that they are using the Cu and Pb electrodes not the other ones
  • Slope of the delta G vs. T is equal to negative delta S meaning that if they get a negative slope they should end up with a positive change in entropy
  • It would be helpful to demonstrate the use of the repipet
  • This lab doesn't result in very accurate data so don't get surprised if your students don't get numbers near to the literature
  • Only the electrode should be in the solution and not the alligator clip
  • Remind them about the 1022 review session on May 9th from 6 to 8 PM in Smith 100 
  • Next week is check out week. They all have to show up!

I would also like to take this opportunity to thank the Monday afternoon TAs who have helped me through this semester with their helpful tips: Roger, Adam, Evan and Nick. Thanks guys!

Have a good rest of the semester :)

 

 

Experiment 16 (Part 1)

Hi everyone,

I hope you had a good weekend.

This lab was quite a long one. Here are the tips that might help you:

- Reminder: This week they hand in their reports at the end of the lab (that's why it takes longer than usual)

- They have to make an agar gel and wait for it to cool down. A good way for saving time is to tell them to get started right away and then give the prelab talk while they're waiting for the gel to solidify

- Walk around and make sure they have figured out the electrodes correctly. There is a very helpful chart beside every board that can be used:

Cu: orangish color, Zn: has a punched hole on it, Ag: not as flexible as Cd and Pb, Pb: flexible and soft (you can scratch it with your nail), Cd: also flexible and soft but not as much as Pb

- If they read zero while measuring a cell tell them to reverse the clips

- Some electrodes develop a black precipitate while reacting. Tell them to sand it off before every measurement if such a thing happens between runs.

- Make sure they are doing the second part correctly (determining the Ksp). It is a bit confusing for them. It doesn't hurt to put a scheme on the board of how one would set up the experiment. Also tell them that in this part they should use the same electrode for both half-calls, same as the cation (for example, measuring AgCl one uses Ag electrodes)

That's all for this week!

 

Experiment 15 (week 2)

Hi all,

This week's lab doesn't take long. Here are the important points:

  • Strongly emphasize that they have to write down the unknown numbers correctly.
  • Tell them that water can be an option for their unknowns.
  • It's better if they don't use their plastic pipettes since they might be contaminated. I told them to use the disposable glass pipettes and plastic bulbs which are located in the bins underneath the blackboards.
  • Remind them that next week is make up session.

That's all for now!

Have a good one :)

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