Slow motion chemistry: A real storm in a teacup

Following on from my slow motion combustion reactions, which were really popular for classroom teaching, I thought I’d try the same formula with another crowd pleasing reaction: Neutralisation with universal indicator on magnetic stirrer.

First reaction was a real beauty, but there was lots of turbulence due to air bubbles caused by the height of the liquid in the conical flask and the high speed of the stirrer.

I decided to film portrait orientation. Although this gives large black bars when viewed online, it gave a really good view of the conical flask and the beautiful swirling purple colours as I added the sodium hydroxide.  It’s a really good talking point for classroom discussions about neutralisation.  -What’s going on?  Why doesn’t it all change at the same time? -Why don’t the liquids mix instantly?  What will happen? Why did it go Blue?

This was the least successful in terms of colour changes, but the vortex is really beautiful and engulfs the stirring bar. I love the final colour.

Genie in a bottle. 

I looked up a recipe from the RSC demonstration handbook for ‘dancing flames‘, which is a reaction between aluminium foil and copper chloride. The acidified solution eats away at the oxide layer, exposing the aluminium for reaction and then generating sweet hydrogen gas for the exploding. Watch the video for the burn:

This is a great experiment that allows a really good and deep discussion of reactivity, and also flame tests.  It’s applicable to KS3-5, and is a great point of focus as a demonstration with the lights off.

Slow motion combustion experiments.

Wanting to illustrate combustion for GCSE chemistry using a classic demo with a new twist, I did a Whoosh bottle experiment filmed at 240fps.  The standard experiment involves setting light to methanol, ethanol or propanol in a polycarbonate water cooler bottle, and the rapid exit/entrance of gases through the neck causes a whoosh.

Filming in slow motion allowed us to discuss in much greater detail what was going on during the reaction, and to work out that the actual reaction is far more complicated than a simple equation.

The experiment was beautiful, filmed on an iPhone 6, and then slowed down in-app using SlowPro.

As an extra experiment, I then tried methanol in a volumetric flask, behind a safety screen in an empty lab, just in case.

A talking point and a teaching point.


Getting the lighting and safety aspects correct! (This is against CLEAPPS advice – never do this in an occupied lab)

Next Steps:

Using a TriggerTrip to take a high-res photo during the combustion process.

Simultaneous combustion of methanol, ethanol and propanol to compare burn rates and completeness of combustion.