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The power of seeing the chemistry in action

Lowell Thomson's picture
Tue, 01/21/2014 - 21:51 -- Lowell Thomson
Distillation of ethanol

As I maneuver through the school year, a certain rhythm develops. The start of the year brings the excitement of new classes and new students. I'm often trying new things in the fall as I've reflected on the previous year's teaching over the summer. The energy level is certainly much higher at this time than almost any other. Then fall quarter comes to a close and report card writing overwhelms the schedule for a few weeks. This leads to parent conferences and the nervousness of students in how that will work out. There's a big push before the winter holiday, which leads into mid-term exams in January and more nervous energy about grades and performance.

That's where I am right now, in the middle of semester final exams for my grade 10 and 11 students. My seniors, on the other hand, are finishing the core of the IB and preparing for mock exams at the end of February.  It's a busy time and I find that I can get into a teaching rut, simply re-using ideas from previous years. One of my goals for this year is to use something new in every class. It doesn't have to be a large idea, but simply a new idea. I'll be the first to admit that I'm not successful in reaching this goal every day. But when I get bogged down marking labs and writing comments, it helps me find inspiration to try new ideas.

So that's just what I did today with my seniors. The students are learning about oxidation of alcohols within the organic chemistry unit. Dichromate is a typical oxidizing agent, and the product of oxidation - for primary alcohols - is either an aldehyde or a carboxylic acid. The choice of distillation or reflux determines the specific product. For preparing aldehydes, distillation is used; reflux will produce carboxylic acids. And teaching the difference between distillation and reflux and why it makes a difference in the product formed is a concept I've always found difficult to get across successfully. I've spent many a lesson in previous years drawing diagrams on the board, showing my students the pictures of the apparatus, and explaining the process. And yet the disconnect between the two methods remained.

Today I decided to show my students the difference. With the help of my school's lab assistant, I set up a distillation and a reflux yesterday in preparation for today. Then I posted the photo below on my Twitter feed to get my students thinking about the concept before class.

 

Oxidation of Alcohols using Reflux and Distillation

 

Then in class, we started the reactions and watched the outcome. For most of the students, this was the difference for them. The actually got to see the chemistry in action. They got to see the aldehyde drip out of the distillation apparatus and compare this with the reflux, where the aldehyde is condensed and returned to the reaction flask for additional oxidation to become the carboxylic acid.  And while this was more of a hands-on demonstration rather than a complete lab experience, the students were engaged in the chemistry going on in the reaction vessels much more than they were in the theoretical discussions we'd had previously about this topic.

As with most new things I try - and even recycled ideas - I polled my students at the end of class about the learning strategy. As a closure activity, students had to answer the following two questions:

  1. On a scale from 1-4, how useful was the demonstration in helping you to understand the difference between distillation and reflux?
  2.  What are the products – under reflux – of the oxidation of the following:

Primary, Secondary and Tertiary Alcohols

 

Question 1 is inherently about getting feedback on the teaching strategy I chose for the day. Question 2 is a chance to collect formative assessment data and see if they got one of the main ideas from the day. And while this question focused on the difference between primary, secondary and tertiary alcohols and their products of oxidation rather than the demo, it gave me a chance to evaluate their learning and make informed decisions about whether to revisit this concept.

The average score for question 1 was 3.32. While there were two students that were below 3, I was pleased with the overall result. A few students added some comments which highlighted the benefit of seeing the reaction take place to understand the difference. And for question 2, I learned that students need a bit more explanation for why tertiary alcohols don't undergo oxidation in the same way as primary and secondary alcohols. That will be the start of my lesson on Thursday.

I guess the take home message I'm trying to share is the idea that really hit home with me today. I need to continue to give my students more opportunities to see and do chemistry, rather than just talk about chemistry. This is always a goal of mine, but sometimes it can get lost in the day-to-day rhythm of the year. This was a good reminder for me.

Do you have a concept that you've adapted to be more engaging or interactive? Please share it here in the comments to keep the discussion going.

 

 

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