1017 Forum

LONG lab today! My last students finished 30 minutes after lab was technically done. Be prepared to warn them that the lab is long - especially if they didn't do their theoretical yields for the CaCO3 from two weeks ago, or if they did it incorrectly.

Here are some thoughts to help lab #8 move along:

* They will check out a Molarity Kit from window, one per two students.
* Assign partners different colors of dyes so each has to do their own dilutions
* One partner can set up dilutions while the other uses the buret, volumetric pipet, and pH meter
* Go over how to do the dilutions step by step - a drawing on the board helps
* The post lab questions are good, but go back and review old stuff (like total ion calculations) so there were many confused students on those.
* By the time the second student was using the pH meter we had problems with getting those calibrated. I think you need to make sure that they turn off the pH meter before re-running calibration. But turning it off can be tough - there were several that I had to repeat the "off" sequence several times before they would actually shut off. And some I couldn't get to recalibrate at all.

The main issues with finishing the CaCO3 lab were

* Students have forgotten how to do theoretical yield calculations
* Actual yields again ended up high in some cases.
* Filling out the observation part could be consolidated into one overall diagram showing which cells had a precipitate

Overall - Finishing the CaCO3 and doing Experiment #8 parts I and II is probably too much to all be finished in one lab period. Last fall we only did Part I so that would be plenty of time, but with all the finicky measurements in Part II we ran over.

Good luck and move them along!

Kim Loomis

Not too much to report today - we only had about 6 students actually making up missed labs, and most of those were doing Lab #5 which landed on the last big snow day.

Several of my students did come in to weigh their calcium carbonate from last week's lab and do their calculations so they wouldn't have to do that next week while working on Lab #8.

One interesting note on the calcium carbonate lab: the majority found they got % Yields of over 100%. The two most common explanations are 1) the product was not yet completely dry 2) there was other "crud" in the beakers that added mass to the product. I would be interested to see the results from the rest of the class who will weigh their product next week - maybe after drying for 2 weeks the results will be more in the expected range (90 to 100%).

Kim Loomis

This morning we did the new Synthesis of Calcium Carbonate and Investigation of Limiting Reactants Lab. In general, FUN Lab and a great replacement for the old Aspirin Lab. I have several tips, suggestions, and questions below that we can also discuss at today's 12:20 meeting:

* Students working in pairs can use glassware from both drawers and can set up the three filtrations to run simultaneously. This cuts down on time needed to do the lab and most were done within 2 hours.
* Have students get about 60 mL of each of the reactants to measure out the trial amounts at their station. There are only two sets of the chemicals set out in plastic jugs in the room so this minimizes collisions
* If you need filter paper ask at the window for a box
* Tell students to stir gently - if they "egg beater" the reactants the particles can become so fine that they produce a cloudy filtrate
* On the table on page 3-5 it asks for g of limiting reactant. I want to check with Michelle if this is really what she wants them to calculate, or if it should be which is limiting reactant, or if it should be g of product.
* Questions 3 - 10 are a bit redundant. It might be easier if they put all their observations together one one drawing. Some of the interpretation questions could also be combined.
* On page 3-10 it says for Disposal of Used Chemical Solutions to put them in "the proper used chemical container" when in fact they are all non-hazardous and can get washed down the drain. There is no chemical container set out.
* Question 11 reacts silver nitrate with sodium sulfate to produce silver sulfate and sodium nitrate. According to their text book and lab solubility table, both of these products would be soluble. Part B of this question references the precipitate from this reaction. I told my students to assume silver sulfate is the solid precipitate formed (which can happen depending on concentration).
* There is nothing to turn in this week because they need the mass of their final dried product. Next week is make-up week and I told my students that they may come in and weigh their dry product and do the final calculation if they want to, but they don't have to. The following week is the Molarity lab (both parts) which may be long and putz y, and they may find the time a bit limiting if they try to do both (but I don't think it will really be a problem).
* Do remind students about the dress code as the temperatures get warmer - no shorts, no sandals
* We will need a grading key - but its not due for 2 weeks

The Reaction Stoichiometry Worksheet today went very well! They don't have their exam on this material until April 11th, so the timing is excellent. What you will find is:

* Some students really understand stoich and will breeze through in less than an hour
* Some students struggle with some aspects, like limiting reactants, but will still get through in 2 hours
* Some students haven't even looked at any of this material and have no clue, requiring all 3 hours
* Some students are not taking the on-line part this semester and have forgotten all of it, also requiring all 3 hours

But even for the ones who needed the most time and help, the repetition of the worksheet is great for helping them to understand the material. I did have several that didn't quite get that for a limiting reactant problem that you must find the amount (moles or g) of the same product to figure out which reactant limits. Many just found moles of reactants and figured that the lower number meant limiting, and in most cases this coincidentally worked out to be the limiting reactant. Just watch for that and make sure they go all the way to the product.

Most important: Next week the lab has been switched! They will NOT do the Aspirin lab but instead the synthesis of Calcium Carbonate. At the stockroom window they will have hard copies of this new lab for you to pick up and pass out to your students. There is a prelab, so make sure you pick yours up and hand it out.

Have fun -

Kim Loomis

Today in lab - lots going on! The weather caused some absences this morning, which was not a surprise. Students will be finishing Lab #4 Determining Empirical Formulas and doing Lab #5 Chemical Reactions Writing Net Ionic Equations. Here are some observations that may help things go more smoothly.

* In your pre-lab talk you will be doing a demo with HCl and Na2CO3 so they can see a gas evolution reaction (they will be writing the equations for HCl with sodium bicarbonate). Show the equations and that the carbonic acid breaks down to water and carbon dioxide.
* Obtain a large test tube from the stockroom window to mix the demo in.
* Go over the molecular, total ionic, and net ionic. I have several students who took the lecture portion more than a year ago and this will be good review.
* There are three sets of the reagents available for each section so they can work at their stations in pairs and share
* I emphasized NOT touching the dropper to anything to avoid contamination, I drew a diagram too
* Check the NR equations - they only need to do molecular and total ionic
* On the worksheet there is a question with the iodate ion - most students are not familiar with this ion and it is not in the book's list of common polyatomic ions, so you may have to identify the iodate for them

You will also have questions on Lab #4

* The instructions are not clear that they are to round the mole ratios to the nearest whole number. Some get bogged down in some pretty extensive fractions.
* They may need help with the last post lab question. They still need to look at the mole ratio of water to the SmCl3 H2O but realize that the ratio is then set equal to X-1
* Some students are really frustrated that their data is off for both MgO and the CuSO4 5H2O. I try explaining that lab data often is not perfect, but some just can't stand the idea of losing any points. We are not taking points off for the MgO, but we are for the copper sulfate pentahydrate.

Time varies by students with some requiring the whole lab period.

Have fun - Kim Loomis

The lab portion of this goes fairly quickly. Again, there are problems trying to get all of the Mg to oxidize. Here are some thoughts for the lab:

* Pick up a box of scissors and polished glass tubes from the window
* I also picked up a large handful of rubber tubing - they are in the blue plastic container in the NE corner of the lab.
* The copper sulfate is by the balances and the Mg ribbon is in a brown glass bottle on the shelves by the black boards
* This morning I tried coiling the Mg ribbon into a spiral with better luck, but ratios still came out high on Mg and low on Oxygen - so there is still some Mg metal that is not oxidizing.
* Some of the ribbons just wouldn't ignite no matter what - I then actually lifted the ribbon out with tongs, lit it and dropped it back into the crucible.
* Use the larger 6" test tubes for the copper sulfate, the 4" tubes are too small to fit in the clamps.
* Check the Bunsen burners and adjust as needed. Some of the hoods are stronger than others and literally blow out the flame. Usually between the two student's drawers, you can find one burner that works well.

The Models lab, Lab #7, went well this morning. There are 90 model kits set out in the SW corner of the room, plenty for each student to have one with only the three sections in the room at the same time. Students vary greatly in their time requirements for this lab - my fastest was out in 1.5 hours, but my slowest didn't finish until 10 minutes after lab was over.

They have had this material in lecture, it was in Chapter 10. But many of my students took the lecture part one (or several) semesters ago and don't remember much about shapes or polarity. I found it helpful to highlight the following items:

* Page 7-4 that C makes 4 bonds, N makes 3 bonds, O makes 2 bonds and H and halogens make 1 bond
* Page 7-5 the hit about ring structures

Many struggled with polarity and with the isomers.

Good luck and have fun!

Kim Loomis

Wednesday morning's lab went very well - we had some outstanding crystals.

Ask the stockroom for a handful of rulers and mention to your students to get some rough dimensions on their sketch of the largest crystal. The stockroom would like the rulers back at the end of the lab period. This semester I only had one student who had no crystals and about 4 who had small crystals, everyone else followed the directions very well and got some very big 1 to 2 cm crystals.

I did eyeball the densities (which should be close to 1.8g/mL) and when I saw some that were off (too high or too low), I had them break their crystals into smaller pieces that would fit into the 5 mL graduated cylinder. Then get a new mass of a pile of these smaller crystals and then transfer them to the 5 mL grad with about 2 mL of supernatent in it. They will get much more accurate volume readings using the small graduate and the subsequent densities looked much better. The 100 mL grad is just not that accurate.

The stockroom does not need the crystals at the end, they have enough from last fall. So all the crystals can get dissolved and washed down the drain.

When all students in the lab room are cleaned up, the goggles can come off to finish the Elements and Compounds Worksheet - coordinate with the other TA's in the room.

The Elements and Compounds Worksheet will take varying amounts of time depending on the students understanding. Overall, I just let them come to me with questions. Problem areas (as always) are when to use a Roman numeral and how to calculate the charge of a transition metal in a compound. The last page mixes ionic and covalent so that also is tougher for them.

Have fun - next week is Models lab.

This morning's Crystal Lab went just fine and was fairly quick.

Again, there are hot plates to use to heat the water bath in the south west corner of the lab. I had my students use thermometers and keep the temp at 50 degrees C - if it gets too hot and they add additional crystals, you end up with too much in solution and get a solid beaker of stuff! Stick with the directions: 35 g potassium sodium tartrate and 28 mL DI H2O at hot tap water 50 degrees.

The seed crystals should be the tiny individual crystals from the stock bottles. Some of my students wanted to use a "chunk" of crystals rather than just individual ones.

Weighing out the crystals again is a messy process!! One method that works pretty well is to tare the 100 mL beaker then remove it from the scale and add crystals up to the 20 mL mark. Then place back on the balance to see how many grams you have. This will get them close and they can again remove the beaker from the balance and add more as needed to get to the 35 g. This seems to help minimize the amount of spilled crystals on the balances. Remember to clean the balances after they are done with them. The potassium sodium tartrate can go down the drain with water as it is non-hazardous.

Make sure they place the watch glass "U" shape direction so it doesn't slide off the beaker.

They only turn in the prelab, but they should also do the post lab during the lab period! Several students wanted to leave right away, so be sure you check their post labs to see that they have done it. Some students will really struggle with the post lab questions and will need help.

The postlab page 6 is missing the roman numeral in the copper sulfate pentahydrate. I edited all so they read copper (II) sulfate pentahydrate. You may have to explain the meaning of the roman numeral II. The formula for sulfate is on the first page of the next lab (Elements and Compounds) in the manual. They should be able to figure out the pentahydrate from the discussion at the beginning of the crystal lab.

The last people left after 2 hours, so you can plan on getting out a bit early.

Kim Loomis

This morning's Crystal Lab went just fine and was fairly quick.

Again, there are hot plates to use to heat the water bath in the south west corner of the lab. I had my students use thermometers and keep the temp at 50 degrees C - if it gets too hot and they add additional crystals, you end up with too much in solution and get a solid beaker of stuff! Stick with the directions: 35 g potassium sodium tartrate and 28 mL DI H2O at hot tap water 50 degrees.

The seed crystals should be the tiny individual crystals from the stock bottles. Some of my students wanted to use a "chunk" of crystals rather than just individual ones.

Weighing out the crystals again is a messy process!! One method that works pretty well is to tare the 100 mL beaker then remove it from the scale and add crystals up to the 20 mL mark. Then place back on the balance to see how many grams you have. This will get them close and they can again remove the beaker from the balance and add more as needed to get to the 35 g. This seems to help minimize the amount of spilled crystals on the balances. Remember to clean the balances after they are done with them. The potassium sodium tartrate can go down the drain with water as it is non-hazardous.

Make sure they place the watch glass "U" shape direction so it doesn't slide off the beaker.

They only turn in the prelab, but they should also do the post lab during the lab period! Several students wanted to leave right away, so be sure you check their post labs to see that they have done it. Some students will really struggle with the post lab questions and will need help.

The postlab page 6 is missing the roman numeral in the copper sulfate pentahydrate. I edited all so they read copper (II) sulfate pentahydrate. You may have to explain the meaning of the roman numeral II. The formula for sulfate is on the first page of the next lab (Elements and Compounds) in the manual. They should be able to figure out the pentahydrate from the discussion at the beginning of the crystal lab.

The last people left after 2 hours, so you can plan on getting out a bit early.

Kim Loomis