Nonpolar goodness.

Helping students see the practical applications of chemistry is one of my favorite parts of teaching. It’s easy to forget the concepts of chemistry unless they are integrated into a student’s already-existing schema via connections to real-life experiences. One such connection is the chemistry of making butter.

Making homemade butter provides a convenient application for polarity, and it also allows you to extend upon students’ previous knowledge of phospholipids from biology by applying chemical significance to explain the properties of the parts of those molecules.

To make the connection, I begin by showing students a picture of raw milk taken at the microscopic level. The milk has fat globules that look like cells. We then proceed to talk about what makes a cell membrane—phospholipids. We draw a basic phospholipid on the board with a circular head and zig-zag tails as in the traditional fashion. I then ask students to tell me what they know about each part of the phospholipid. They normally mention that the head is hydrophilic (water-loving) and the tail is hydrophobic (water-fearing). I then ask them to tell me what kind of molecule water is (polar), and we then proceed to talk about how “like interacts with like.” Polar interacts with polar, nonpolar interacts with nonpolar.

For PowerPoint slides with these visuals, click here!

Next, I ask students to make predictions about what kinds of elements we may find in the chemical structure of the phospholipid head if it is polar. They normally predict O, F, N, etc. I then ask them to make the same prediction about the nonpolar tails. They normally predict C and H. We then proceed to examine the chemical structure of the phospholipid. Indeed, as they predicted, there is a phosphate group in the head with several molecules, and the tails are made up of chains of carbon and hydrogen. It is really neat to show students how the chemistry they have been learning explains the properties of molecules they have already studied in Biology.

We then proceed to talk about how fats are nonpolar (They have long chains of carbon and hydrogen.) and therefore are found on the inside of the milk “globules,” with the membrane consisting of a single layer of lipids, heads pointing out, tails pointing in toward the fat molecules inside. We then discuss that we need to break these membranes if we want to get the fat molecules out of the “cells” so they can clump together to form butter in all its nonpolar goodness.

So, we then take some heavy cream and let it sit out at room temperature for about four to five hours. We then fill a pint mason jar halfway with the cream and place a marble or decorative stone inside the jar. We close the lid and then have fun passing it around the class for students to take turns shaking. Up and down, up and down, up and down. :) As we shake, the cream turns into heavy cream (at which point you can no longer hear the marble bouncing around). Then, if you keep shaking long enough, the whipped cream will separate back out into butter and buttermilk. You’ll be able to hear the buttermilk sloshing around along with the sound of the marble.

Next, take the butter out of the jar, rinse it off in cold water and then squeeze it with a cheesecloth to remove excess moisture. If you plan to keep your butter for longer, it will maintain its freshness better the more moisture you can remove.

…and finally, enjoy that nonpolar goodness! I had made homemade sourdough bread for my students to sample it with. :) A memorable time was had by all. I told my students that I knew they would like the concept of polarity all along. :)

Here are a couple of links to homemade butter recipes:

https://thestayathomechef.com/how-to-make-homemade-butter-in-a-mason-jar/

https://happyhooligans.ca/homemade-butter/