This lesson could fit whilst teaching equilibrium, redox, chemical/physical reactions or just learning about the scientific process. I try to blend scientific thinking in wherever possible, and this is a great one with minimal focus on the “right answer” but instead focusing on thinking like a scientist.

HOW TO SET IT UP

I use the blue bottle recipe from RSC  (make sure you make them fresh that day) to create enough flasks for one per table. I don’t tell the kids what’s inside the flask, but you do need to make sure they keep their goggles on.

I normally let them have a play with the reaction whilst the class is filtering in. Watching it turn blue when you shake it and then turn back to colourless is super mesmerising for most kids.

KEY QUESTIONS

“What do you observe?”

“What hypotheses do you have for your observations”

“What experiments could you do to test your hypotheses?”

HYPOTHESES AND POTENTIAL EXPERIMENTS TO TEST

This is definitely not an exhaustive list… let me know if your kids come up with something different!

1. “The cap of the flask could be reacting with the solution” – could be tested by replacing the lid with your (gloved!) thumb/sellotape across the top of the flask and shaking to test
2. “Shaking it causes the colour change” – can be tested by swirling the solution or shaking it with minimal gas in the flask.
3. “The air is causing the colour change” – can be tested by pouring the solution from a height or by filling the solution almost to the top of the flask and then shaking.
4. “Any gas will dissolve in the solution and cause the colour change” – test by bubbling methane through the solution.
5. “The nitrogen in the air is dissolving in the solution and reacting” – can be tested by bubbling nitrogen through the solution
6. “The oxygen in the air is dissolving in the solution and reacting” – can be tested by generating oxygen (manganese dioxide and hydrogen peroxide) and bubbling through the solution.

This experiment for me isn’t about “right answers” – it’s more about students making a final hypothesis based on the tests that we do in class.  If you’re on the hunt for one then use the RSC link which goes through the actual Chemistry behind the reaction and is really great at explaining the redox behind it all!

Any other suggestions/feedback greatly appreciated!