Chemistry Experiments: Colors (surface active agents and pH indicator)

Our new MEL Chemistry box arrived, containing tons of color fun! We have already tried two experiments. In the Color changing milk experiment, the soap touches the milk creating a very thin film of soap on the milk’s surface and causing the colors to spread along with it, producing a mesmerising effect. Molecules of soap and other similar substances lower the surface tension of different liquids and thus are called surface-active agents (SAA). Simon took it a notch further and created antibubbles that glide on the film of soap:

 

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We thought this one looked like a nuclear explosion:

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The second experiment we did was called Magic Liquid and felt like performing a magic trick: a yellowish liquid poured in five different cups turned five different colors, almost all the colors of the rainbow! The secret was putting a tiny bit of a different chemical substance on the bottom of every cup beforehand. The yellowish stuff was actually Thymol blue, also known as thymolsulfonephthalein (chemical formula C27H30O5S ), a pH indicator, and changed color according the acidity of the substances that were already in the cups. The larger the quantity of protons H+, the higher the acidity of the medium, while the OH ions are responsible for the basic medium:

 

Thymol blue molecule visible on the iPad screen:

We also checked the pH of the substances using indicator standard teststrips:

The pH rainbow:

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Simon had already been busy with colors for a few days, revisiting his Magformers collection to build this gorgeous color wheel:

We later repeated the MEL Science demos for Simon and Neva precocious friend:

 

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