MEL Chemistry Experiments: Flames and Minerals

Monday was a chemistry day as we went to the post office to fetch our brand new delivery from the MEL Science subscription! We set a record of 6 chemistry experiments in one day! We just couldn’t stop, maybe because all of the experiments involved fire.

We started with the Minerals box. The first experiment was about heating up some semiprecious stones, amethysts (a species of quartz widely used in jewellery). The nature of amethyst’s color is still a mystery: some theories suggest that the color is of organic origin because it changes when amethyst is heated. Our purple amethyst became completely white after we heated it!

Simon watching the solid fuel burn (C6H12N4 – hexamethylenetetramine)
solid fuel C6H12N4 – hexamethylenetetramine – burning with the amethyst wrapped in aluminium foil on top of the flame diffuser
Amethysts in their original color
Amethyst has become white

We also repeated the same experiment with a piece of red coral.

Chemically, coral consists almost entirely of calcium carbonate CaCO3—the same compound chalk is made of (plus the red pigments known as carotenoids). When coral is heated, a strong smell should arise, because of the organic remains left in the skeletal structure. We didn’t really smell much, the coral seemed unchanged after heating:

What we did next was dissolve some malachites! We used NaHSO4 (sodium hydrogen sulfate) as an acid that the mineral would react with and heated the solution up to speed up the process. The big question was: will the malachites dissolve? And will a certain metal come free as a result?

Pieces of malachite in a beaker
The solution turned blue when heated
We added K4[Fe(CN)6], or potassium ferrocyanide, to the solution to detect metal ions. The indicator substance turned brown, which indicates copper ions!

Malachite is a mineral that contains copper Cu! In fact, malachite consists of (CuOH)2CO3 – basic copper carbonate. This compound has been used as a source of pure copper since antiquity, the MEL Science website explains. 

What was left of the malachites

Now it was high time for some fireworks!

This one was our favourite! We performed it many times, just to see the mesmerising green sparkles. All one has to do is dip a stick in paraffine, then in CuSO4 (copper(II) sulfate) for 30 seconds, then in paraffine and (very briefly) in water. This creates a kind of homemade sparklers, like the ones popular on New Year’s Eve, spitting spectacular flashes of green.

What made the flame green is its copper Cu2+ component. Metal ions such as copper ions Cu2+ can emit light of a certain color when heated to high temperatures. Copper emits green, while rubidium Rb creates red and sodium Na creates yellow, and so on. You can create colorful fireworks, but you can also detect which metal is present in a sample by examining the color of the flame.

What else should we burn? Magnesium! Because it lights up so pretty:

From a chemistry perspective, burning is the process of giving electrons to oxygen O in the air, releasing a lot of heat and light. One of the most obvious trends in the periodic table is that the elements on the left side of the table are generally more willing to give electrons away than the ones on the right. But, as we learned from our last experiment called Rocket Fuel, not only oxygen can take electrons from the fuel, in other words, there are other substances that can act as the oxidant (the substance that wants to take electrons from the fuel). If you want your fuel to burn without air, you have to include your own oxidant too. This is how space rockets work.

In our experiment, we mixed the oxidant, calcium nitrate Ca(NO3)2 and the fuel, potassium ferrocyanide K4[Fe(CN)6] that doesn’t burn very well in air (used as fuel for small model rockets and fireworks), and heated them up. When we later set the mix on fire, it didn’t quite produce the effect we had hoped for, the flame went out too quickly to take a good picture.

The oxidant and the fuel
A porridge of oxidant and fuel, calcium nitrate Ca(NO3)2 and potassium ferrocyanide K4[Fe(CN)6]
The very end of the rocket fuel flame burning

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