Science of Fireworks
“Science of Fireworks” – this interesting and educative science experiment and science demonstration was conducted at Science Park, Savitribai Phule Pune University to mark Science Day on 28 February 2020. Please find below a write-up shared by Dr. Supriya Rishikeshi, who conducted this fascinating chemistry experiment and science demonstration along with her team. Here is the video of this chemistry experiment and demonstration.
Mystery behind Fireworks
Why firecrackers give BANG!!!! and light of different colors.
The bright sparkles in fireworks come from burning small bits of metal, such as iron or steel filings. The basic material used for burning is known as “gun powder” Gun powder has its origin in China around 900 years ago. The first script found called as “Essentials of the mysterious way of the true origin” are in Chinese language which says gunpowder is a mixture of Honey + KNO3 + Sulphur.
Here honey was used as a source of carbon. Finally we have used charcoal powder as a source of carbon. Nature of charcoal is very important in burning charcoal. If you prepare gunpowder with chemically very pure carbon like graphite powder, it doesn’t work very well. There is something very special about charcoal made from burning of wood. Electron micrographs of wood charcoal clearly shows sponge-like porous structure.
Optimised ratio of gunpowder is KNO3 : Charcoal : Sulphur as 75 : 15 : 10 ratio. Now to understand how KNO3 is a source of oxygen, we have painted a big K of a solution of KNO3 on paper with a brush and ignited a single point with a incense stick, it burnt painted big K. There is 5% Oxygen available for burning anything in air that too one has to fight to get it. But when we use KNO3 we have Conc. oxygen readily available for burning / combustion, so it is the source of oxygen, called an oxidizer.
We have weighed the proportions already and mixed them in front of the audience in paste and mortar. We burnt various mixtures in a V shaped 2 ft long rod and recorded the burning time. Took the reading on a stopwatch. For comparison we have burnt the commercial gun powder of the same weight and observe the time required to burn it entirely.
Why does commercial gunpowder take less time to burn?
Rate of the reaction depends on the size of the particle. Somehow if we could reduce the particle size and if we get a much better mixing of fuel and oxygen then we will get a much faster combustion. Churning of gunpowder is an important step in activation. Burning of churned gunpowder shows better results. Explained to the audience the details of the gunpowder churning machine.
Third ingredient in gunpowder is Sulphur. S has low boiling point and it helps KNO3 in combustion. For bang, one has to speed up the reaction. There are 2 ways with which one can increase the speed 1) Increase the density, 2) Increase in concentration. When we confine (make pellets) pyrotechnique composition, it burns very fast.
The bright sparkles in fireworks come from burning small bits of metal, such as iron or steel filings. Took fine iron powder in a pinch and put it in a flame to show them sparkles. Aluminium powder will also have the same effect. Different metals give different colors in flame. We have prepared 6 metals salt solutions of SrCl2, CaCl2, NaCl, CuCl2, KCl, LiCl in different beakers and labeled it. Wooden splints have been soaked in the solutions overnight.
We put the point of the splint in the flame one by one and showed the characteristic color that the metal produces.
Khula Aasmaan Videos
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