Colouring of Flames - Flames Reveal Elements

1. Experiment:

You need:

• A burner
• A magnesia rod
• Various powdery substances that contain metals

The Procedure:

At first, our assistant Christian showed us what to do. He lit the burner and took a thin magnesia rod, which he had put into the flames first to remove any possible contamination. This is called annealing. Afterwards, he dipped the rod in one of the powders before putting it in the flames again: We noticed that the flame changed to a strange light green! The reason for this was that the powder contained barium.

Explanation:

But why does the flame turn green? Our assistant explained the experiment as follows: the flame discolours, because the electrons get a lot of energy from the heating and are able to jump from the inner shells to the outer shells. Afterwards, the electrons have to return to their shells. On that occasion, they release energy, which can be seen in the colouring of the flame. The table below shows some components and the colours they yield. It is said that the respective element possesses a characteristic flame colouring.

Our group observed the following colours, although we did not always agree on the actual designation of each colour:

2. Experiment:

After we had studied the characteristic flame colourings of the several powdery substances, we got three samples where we did not know which metals they contained. We had to find out on our own. This was not easy, as some metals have almost the same flame colouring. Therefore, we had to compare them to a reference substance. We did this by putting a rod with our sample and a rod with the presumed substance into the flame next to each other.

Here are our results: