This lab (III-4: Observing double replacement reactions) is from the chemistry kit manual, CK01A and involves a lot of different chemicals and pipette work. Basically, the students take a grid of reaction wells and place different chemicals in each column of wells and then different chemicals in each row so that each well has a different combination of chemicals. The wells are very small and you only put a few drops in each one. The chemicals all came in the kit I purchased from the home scientist but I either misplaced one or it was missing from the kit so we just treated that row as a control group. Most of the chemicals were at 0.1M concentration already but a few of them required the students to dilute them using a 24 well reaction plate and pipettes. We had 4 lab groups but we only had to do the ‘dilution’ procedure twice because we figured it made enough of each chemical for 2 groups, so not everybody did that procedure.
This lab was a good exercise for the students, not just in using a pipette but also in paying attention to detail and making sure they or their lab partner weren’t cross contaminating the reaction plates or chemical sources. I had never used a reaction plate before so this was all new to me and to be honest I almost skipped this lab because filling a 96 well reaction plate (see photo below) sounded a bit intimidating, but it worked out really well and I’m glad we did it.
One thing I did to make the lab a little easier was download reaction plate templates ( you can see one in the photo below) so the students didn’t have to spend time making a big table in their lab books. The table in the lab manual was the opposite orientation of the reaction plates so I didn’t want to use those. I used templates that looked just like the actual reaction plate so it was easy to follow.
Students worked in pairs so we had four 96 well reaction plates to fill. We actually got an assembly line going so we didn’t have to wash as many pipettes. One pair would fill a row of wells with one chemical and then pass it to the next group. As far as I can tell nothing was cross contaminated so well done teens! Even though they were only putting two drops of chemicals in the wells, when they put the second set of two drops some of the reactions were quite impressive with the solutions completely changing into powders or suddenly turning black! Photos were taken of the reaction plates on black and then on white paper and we lit up the reaction plates with flashlights while the students were dropping reactants into the wells so they could easily watch for bubbles (gas), precipitates and color changes – which they recorded on the templates.
We barely finished in 2 hours so I don’t think the students had much time to process the results, so we’l talk about those at the beginning of the next class. But I think the main benefit of this lab was teaching chemistry lab skills. I highly recommend this lab.