by Srinivas Rao – Hooray!! We are in the week of celebration of Diwali – the festival of lights, bursting crackers and fireworks!
Nowadays we get varieties of crackers from different manufacturers. Whenever you burst crackers you see different colors, right? Ever wonder why?
There’s also a lot of chemistry behind the colors that fireworks produce. Here, we take a brief look at what causes the fascinating colors in fireworks.
Fireworks color is determined by the chemicals mixed with the metal:
Red: Strontium nitrate, Strontium carbonate, Strontium sulfate
Orange: Calcium carbonate, Calcium chloride, Calcium sulfate
Yellow: Sodium nitrate, Sodium oxalate
Green: Barium nitrate, Barium carbonate Barium chloride, Barium chlorate
Blue: Copper chloride, Copper carbonate, Copper oxide
Purple: Copper and Strontium compounds.
It reminds me of my undergraduate class, when I was working in a Chemistry lab doing qualitative analysis of organic compounds. We used to identify the compounds by taking a pinch of compound on a spatula and introducing it to the Bunsen flame resulting in different colors with respect to each element. This is the key characteristic feature of alkali metals (left red column), alkaline earth metals (orange column), and a few transition metals (rust color) in periodic table shown below.
If an atom or an ion is excited by very strong heat, electrons will be promoted from their normal unexcited state into a higher excited state or level. As they fall back down to lower levels either in one go or in several steps, energy is released as light. Each of these jumps involves a specific amount of energy being released as light energy, and each corresponds to a particular wavelength. As a result of all these jumps, a spectrum of lines will be produced, some of which will be in the visible part of the spectrum. The color we see will be a combination of all these individual colors.
So let’s celebrate this Diwali with Chemistry!