In chemistry we sometimes use ‘ flame tests‘ to identify metal ions from their colour. Fireworks contain metal salts, to create the brilliant colours that we see in the sky. As they fall back down to lower levels (either in one go or in several steps), energy is released as light. When metal salts are heated, they can emit light if you excite an atom or an ion by very strong heating, electrons can be promoted from their normal unexcited state into higher orbitals. Have you ever seen a saucepan boil over on a gas hob? If there is salt in the water, you see the colour of the flame change colour. If you have a pair of transition lens glasses, this can be demonstrated with a UV torch.Ģ) Using heat to produce light from metal ions When we go outside and UV light from the sun irradiates on these lenses, a reversible chemical reaction happens, which changes colour to make the lenses go dark. In this demonstration, there are 4 different concepts to introduce: transition lensesġ) Using light to drive a chemical reactionĬan you think of an example where we use light to drive a chemical reaction? This is called photochromism, and is used in colour-changing lenses. Do not look directly into the UV-torch and be careful not to shine it directly into the eyes of the audience. It is advised that the demonstrator wears goggles for these demonstrations, and that the experiments are conducted at a distance from the front row. Please download and read the Safety Card before trying this activity. metal salts (NaCl, CaCl 2, CuSO 4, K 2CO 3, FeCl 2).Bunsen burner (you can buy burners that attach to camping gas canisters, for venues without gas taps!).inexpensive UV LED torch from Moobom, online retailer) From primary school pupils through to adults, this demo lecture relates to everyday examples of light and chemistry, including fireworks, colour-changing glasses, glow sticks and security markings on bank notes!įor this lecture you will need the following: A short demonstration about the interaction of light and chemistry can be appreciated by all age groups.
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