Should I Get My Mole Checked Out?

Pre-lab setup:

For advanced/honors students, consider having them do their own full set-up and clean-up. With this option, little teacher preparation is needed. Just make sure the supplies exist (if possible, don't even get them out of the closet or storage—have the students do that, just like real scientists).

If you're setting the lab up for the students, both solutions and lab stations need to be considered. The solutions aren't time sensitive, so you can do them the day before with no problem.

Prepare the 0.50 M NaClO solution by diluting 745 mL of bleach (if it's labeled as 5.25% NaClO by mass) with distilled water to get a total of 1.0 L (each group will probably use about 200 mL, so adjust the ratios as needed). If using Ultra bleach (6% NaClO by mass), use 653 mL of bleach and add enough distilled water to bring the entire solution to 1.0 L.

Prepare the 0.50 M Na2S2O3 in three steps (the sodium thiosulfate produces the best result when created in a basic solution). First, dissolve 124 g of Na2S2O3 * 5H2O (or 79.1 g of anhydrous Na2S2O3) in 500 mL of distilled water. Then, add 8 g of solid NaOH and stir the mixture until all dissolved. Finally, add enough distilled water to bring the total volume to 1.0 L (once again, each group will probably use around 200 mL, so adjust as needed).

Ensure that each station has a temperature probe and collection device (or a thermometer if you don't have LabQuests, EasyLinks, or CBLs), pipettes (two per station, one for each reactant), two styrofoam cups (or a cup and lid), and a graduated cylinder (calibrated at least to 1 mL). If available, provide a ring stand with utility clamp to hold the temperature probe. It is not necessary if not available.

Day of lab:

Assign students to groups no greater than three, if possible. This is to make sure conversations are happening and each student is still involved and active.

Using the strategy Thinking Notes, have the students read through the procedures and pre-lab questions, putting stars next to steps that directly relate to data collection, an exclamation mark next to details about measurements (for example, the specific volume, or not just initial temperature but temperature readings throughout each trial), and question marks where the procedures are confusing or unclear to them.

Have the lab groups discuss and answer the pre-lab questions, reflecting back to the procedures to add stars or exclamation points and/or to see if the answers clear up confusion.

Once students have finished their pre-lab questions and found resolutions to the confusing parts of the procedure, direct them to their lab stations and instruct them to get started collecting data.

Walk among the groups to help troubleshoot, but try not to take over if it isn't perfect; students need to learn the subtle art of exactness through their own experiences with only gentle prompts from the teacher.

Explain to students that they will be combining different ratios of reactants, starting with equal volumes of each (thus a 1:1 ratio) and keeping the total volume the same but shifting the amount of each.

If students are stuck with what amounts they should choose, nudge them in the direction that would give them less than 10. Whole number ratios, like 20 mL of NaClO and 30 mL of Na2S2O3 is a 2:3 ratio, but 12 mL of one and 38 mL of the other is a 6:19 ratio. If the students want to try the weird ratios, though, let them. They can still get usable data points from them; they just won't be the right answer.