Experiment 5 - Chemical Calorimetry

Lab reports are due next week - I had about half of my class turn theirs in today.
They should weigh their product from Exp 3 which should take no more than 5 minutes - if you didn't have them prepare their %yield calculations before they left last week, you might want to email them a reminder to have them prepared before they come to class. In my prelab, I discuss why their %yield is greater than 100% because almost everyone is confused.

Remind them to remove the protective sleeve on the digital thermometers before using them. Also remind them to use the same well in the pink Styrofoam calorimeter for each trial.

I discuss specific heat in my prelab and have them visualize boiling a pot of water - the pan gets hot faster than the water does, which accounts for the difference in Csp for water and aluminum. I also discuss practical uses for calorimetry so they understand that we aren't just trying to torture them with math in this lab.

Part A:
The calculations are well described on p 5-7. Some get confused about finding the mass of the solution using the density of NaCl or what to do since the 1.0M concentration of NaCl doesn't match the 2.0M solutions they started with.

For Q7, some students assume %error is the same as %yield. It's not. Have them see Appendix A. I saw %errors ranging from 6% to 30%.

Part B:
Set up a 600mL beaker with about 15pcs Al in boiling water. The students should bring their tongs, calorimeter, thermometer and partner to the Al and transfer the metal quickly. They can monitor the temperature while walking back to their desk

Have them show you their calculation for the first trial of their calorimeter constant. It should be between 0 and 15.

Part C:
I had no questions about this part, though the %errors here were much greater than that for the enthalpy of neutralization (between 50 and 150%)

Neutralize acid/base and pour it down the drain.

About this Entry

This page contains a single entry by amaxwell published on February 28, 2011 5:18 PM.

Experiment 3 Synthesis of Calcium Carbonate was the previous entry in this blog.

Experiment 6 - Atomic Spectrum of Hydrogen is the next entry in this blog.

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