Burple and the ‘pop’ test

In my last blog I described the colour of hydrated cobalt (II) chloride, CoCl2.6H2O as deep purple, but the more I look at it, the more burgandy red it appears. So I think I’ll settle for a burgandy-purple or ‘burple’ colour. Of course, I just made that up, but it does illustrate the problem of describing in words the colours we see with our eyes. For the chemist, this includes the problem of describing the many varied colours of transition metal salts.

I also asked last time what was the standard test for hydrogen gas in the school chemistry laboratory. It is of course, the burning splint test. More often this is referred to as the hydrogen “pop” test, because introduction of a burning splint into the gas causes it to burn with a small explosive “pop” and this is shown below.

A burning splint causes the gas to ignite with an explosive "pop"

A burning splint causes the gas to ignite with an explosive “pop”

The hydrogen was generated by adding a small length of magnesium ribbon to dilute hydrochloric acid.

Another way to ignite the hydrogen is to use a piece of platinum foil that has been heated red hot in a Bunsen burner flame. This is shown below. Unfortunately, the flame produced was still coloured orange, presumably due to trace amounts of sodium and other contaminants. Hydrogen is reputed to produce a colourless flame.

Hydrogen ignited by red hot platinum foil

Hydrogen ignited by red hot platinum foil

In both of the above explosions the hydrogen gas is reacting with oxygen gas in the surrounding air.

Oxygen can be generated in the school laboratory by the decomposition of hydrogen peroxide solution, catalysed by manganese (IV) oxide. The test for oxygen is to use a glowing splint which rekindles in the oxygen gas and bursts into flames.

A glowing splint bursts into flames in oxygen

A glowing splint bursts into flames in oxygen

What is the test for carbon dioxide gas in the school chemistry laboratory?

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