When I was in school I always looked forward to the day when I would finally get to do “real” science. The image in my mind was one of lab coats, Bunsen burners, chemicals, and explosions a la mad scientist:
Science never really lived up to my (unrealistic) expectations. Now, as a teacher, I understand why (not in the curriculum!), but I do want my students to experience that sense of “mad science” wonder whenever possible. Thus, I build up the hype about the chemistry, matter, and energy unit and like to start off with a bang…or at least a few chemical reactions.
This lesson works well as an introduction to chemistry or as a mid-unit bridge between chemical and physical changes (lesson coming soon) and balancing chemical equations. All you need are a few standard chemicals, potassium iodide and lead nitrate being the most unusual, zip baggies, pipettes, and space to set up work stations.
I like to start off the lesson by discussing the term “indicator.” An “indicator” is something that lets you know something else has happened. A few student-friendly examples:
- a red light is an indicator you should stop
- mold is an indicator that your bread is old
- a flash from your phone is an indicator you have a message
- a “thumbs up” on Instagram is an indicator someone likes your post
- a pregnancy test is an indicator you’re going to have a baby
We can’t see individual atoms and molecules interacting, so we have to use other indicators to know when a chemical reaction has occurred.
In today’s lab we will be looking at 4 different indicators of chemical reactions:
- [Unexpected] Change in temperature
- [Unexpected] Change in color
- Production of a Gas
- Formation of a Precipitate
I include [Unexpected] in that list to reinforce the fact that freezing/melting/boiling are PHYSICAL, not chemical changes and painting/dying is a PHYSICAL, not chemical change.
You’ll need to have four stations set up in advance with materials and instructions:
- [Unexpected] Change in temperature – baking soda + citric acid mix, calcium chloride (DampRid), water, pipette, zip bags
- [Unexpected] Change in color – Bromethyl blue, water, test tube, straws
- Production of a Gas – Calcium carbonate (tums), water, pipette, petri dish or beaker
- Formation of a Precipitate – lead nitrate, potassium iodide, chem plate, pipettes
Be sure to review safety rules and have students wear safety goggles!
Students use a foldable to record their observations while going through all the stations:
At the end of the lab rotations I have students meet with people from another group and compare responses. Then we discuss and go back and apply the indicators to a previous activity about chemical vs. physical change to ask for each chemical change which indicators they saw.
Chemistry is fun! Hope you enjoy this activity.