Qualitative Analysis of IONS

supplies for ion qualitative analysis lab

So this time of year we are all thinking about what we will do with our AP Chem students until the end of the semester. Last year I wrote about a post AP independent study activity that I use dealing with transition metal compounds. I still like it and use it. But this year I want to talk about a very involved lab that many of my colleagues are ignoring.

I am doing the classic Qualitative Analysis of Cations and Anions that is published by Flinn Scientific. If you are unfamiliar with it, it is a lab that takes many hours to do. It separates six cations and six anions by very chemical means. It was a mainstay of laboratory programs 50 years ago. Flinn has reworked it to remove a few troublesome ions (Mercury and lead but I think they should still be there).

The advantage to this lab for this type of activity is that it takes almost two weeks of my one hour class periods. The two weeks following the AP exam is pretty hectic and unpredictable for my students. They are all in a variety of AP classes and I do not ever know how many will be out on any given day. So I like that I can set this lab out and let them work at their own pace. It is a very nice opportunity for me to talk with each of them in depth to get a feeling for what they understand and what they don’t. It is a great time to talk with each about their lab skills and help them develop them further in a very relaxed atmosphere. I typically stay afterschool one day and give anyone who wants a chance for two hours of uninterrupted time to work on the lab if they need it. Kids work at their own pace and it is a nice relaxing way to spend to otherwise stressful weeks.

The grading of this activity is very simple for me. After the students have had a chance to run through the whole scheme I give them a bottle with three to four unknown cations and the same for anions. I have them identify what is present and give them five points for everyone they get correct and take off five for every mistake. It only takes me five minutes to grade an entire class set of this lab.

I do want to mention that setting this experiment up was no small undertaking. It required about ten hours and a great deal of money. Many of the chemicals needed to be ordered because they were not typically in my stock room and I needed to get three hundred dropper bottles to accommodate the 8 stations of 4 kids each that I run for lab. I also needed to get a table top centrifuge which I surprisingly discovered I had never purchased before. But the good news is that I figure after my initial outlay to set the lab up I can probably run it for 25 years without having to buy any more supplies. It takes a great deal of storage space but it sets up quickly and easily once mixed.

I am very fond of the phrase “Spending time to save time”. I love a good experiment that I can prepare and then box up for easy use next year.