Last week was the week before senior exams. My L1 class had just finished an internal the week before, as had my L2. I felt assessmented out before assessment week had even begun.
Luckily, my year 10’s have been doing good old acids and bases. A big part of how I deliver this unit is based around acids and bases in nature, so ocean acidification due to increasing CO2 is something we spend some time on. Shells in acid go quite porous after a while, and different types of shells react differently in acid.
To this end, I picked up some dry ice on my way to school to show what happens when CO2 bubbles through solutions. And then, we had fun – so here is some ways I used the dry ice with my classes
Water Acidification (Ocean acidification)
A very easy demo – fill a gas jar (or any biggish jar) with a dilute alkali solution (I used NaOH). Add some universal indicator, drop in a chunk of dry ice, and watch the colours change due to the decreasing pH of the solution. For all of my classes, this was a good revision of the pH scale, indicator colours, relative ion concentrations and for the L2 & 3 chem, strong and weak acids.
This also lead to really good discussions with all of my classes that day (Yr10, L1, L2 & L3) about why the gas was ‘cloudy’. Carbon dioxide is colourless, the cloudiness actually comes from water vapour (think steamy breathe on a frosty morning) and also about why the gas rises when the dry ice sinks with my Yr 10s… density is a weird concept that some still aren’t quite comfortable with yet.
Just add dry ice to water for instant awesome
just the cauldron look is memorising. Swishing your hands through the cold gas is creepy, a year 10 asked if this was what a ghost would feel like. The container eventually froze to the bench, which lead to a discussion around condensation and water vapour in the air.
For my seniors, we got into quite an involved discussion around enthalpy change. It requires energy for the bonds to break in the dry ice to release the gas. This cools the temperature of the water. Which can then result in the water freezing (ice), which means that the water is making bonds and releasing energy.
If you want to go a step further, add some dishwashing liquid
And you get lovely water vapour filled misty bubbles. There is something every satisfying in popping these bubbles, but they are also intriguing to look at, as usually bubbles are transparent and colourless, not cloudy and white.
Normally I’d do this with latex gloves, but balloons were on hand so we used those. It was a really nice reminder about solids vs gases for most of my classes and how the gas particles are more spread out. But with the my L3, I talked briefly about entropy, and how the gas particles are more disordered, so even though it was an endothermic reaction, it was still spontaneous.
What dry ice lesson would be complete without blowing stuff up. When I was at university, a lab mate and I were constantly filling little Eppendorf tubes with dry ice and putting them under each others chairs. Old camera film canisters are perfect, or a berocca tube will work quite well too.
Putting out a candle
Didn’t get a pick of this one, but a really nice, easy thing to do is to leave some dry ice in a container for a while. Light a candle and pop it in a bowl. Then pour the CO2 gas over the candle and it will go out. It is really cool – and convinces the non-believers that there really is something going on.
If you can get some methanol or ethanol, you can make a really good slurry with the dry ice. Which you can then freeze stuff like flowers in – all of my students loved this, and the poor old spring daffodils in the garden took a bit of a hit 😦 It was especially good for my L2 Chemo students to talk about boiling points and melting points of different substances, and why does water freeze when the alcohols didn’t.
So, I got a whole lot of ‘exam revision’ out of my seniors by simply having something for them to play with. I had some of the best learning conversations I have had all year with students looking to make a mess. Some of my students who were really struggling with concepts around enthalpy and bond energies had some good light bulb moments. On a terribly selfish front, I had such a fun day playing with dry ice. Even after 4 lessons in a row, it didn’t get old, and the ideas are adaptable for different levels.
Which reminded me of the need to play. Learning through play is really nagging at me at the moment – Mr 2 almost 3 is a daily example. But even with my knowledge around how useful, important and enjoyable it is, I still don’t always make time for it. So I need to MAKE the time.
So, my next project will be for L1 Science exam revision – we are going to make one of these 🙂 hopefully we can get it to work – and do some tinkering and playing around on the way.
NB. If you are going to use dry ice in your class and want some safety tips, feel free to get in touch. But do be aware that dry ice burns can be serious, and HURT!!
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