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Chemistry of Colour in Fireworks

By JESSETHEBUSH Apr 27, 2014 1143 Words
What is the Chemical Basis of Colour in Fireworks?

Abstract:
The purpose of the first experiment was to see the light spectra of different elements, and confirm that each element shows unique emission spectra, in terms of being able to identify an unknown substance. The analysis is expected to show that elements do indeed have unique emission spectra, allowing elements to be identified by their emission spectra. After burning different chemicals under a Bunsen burner, the colourful light was observed through a light spectrum, giving a reading which was recorded. The chemicals all gave off different colours which, when observed through the light spectra, either had a continuous band or, single stripe. Judging by the matching colours and spectrum readings, it is clear that the unknown substance was calcium. The analysis showed that elements have unique emission spectra; this is significant as it allows elements to be identified by their emission spectra. The online experiment with photo-electric effects displayed the effect light intensity and frequency has when photons are bounced against sodium metal. The analysis is expected to show that electrons will dislodge from the metal when photons hit it, adjusting the intensity and light frequency will affect the quantity of electrons dislodging from the sodium metal. A number of questions were answered backing up the analysis which shows that increasing the intensity will cause more and more electrons to dislodge from the sodium metal. And longer frequencies of light tend to increase the amount of electrons.

Essay
Fireworks have been lighting up our night skies for years. The light and colour of these fireworks can be explained through chemistry after understanding the composition of fireworks, colour, photons, wavelength, frequency, energy levels, white light and wavelengths emitted from compounds.

Fireworks were discovered around 2000 years ago in China; they were originally used in New Year’s celebrations and have slowly been improved over the years. (Anne Marie Helmenstine, 2013)

The human brain and eye turns light into the colour we see. Colour is the perception of all the different wavelengths of light in the visible light spectrum. Infared and ultraviolet light are not defined as colours because they are outside of the visible light spectrum and are not visible to the human eye. A photon is a particle of light with no mass or electric charge. (Conjecture Corporation, 2013) Fireworks have light which makes them visible in the dark.

All elements have varying amounts of electrons which revolve around the nucleus on different shells or energy levels. These fill from the middle, outermost shells being capable of holding more electrons. (Refer to Appendix B)

If an electron absorbs enough photons, it will jump out an energy level, when this happens the electron is in an excited state. Going the other way, when an electron jumps back down an energy level, it must give off some energy; the atom does this by emitting photons. This is what causes the light created from fireworks. (Skyserver, 2013 )

Light Intensity is the rate at which light is delivered to a surface. The light energy depends on both the light intensity and the wavelength (Physics classroom, 2012). If light intensity is higher, the fireworks will appear brighter.

Fireworks are usually made up of: oxidizers, binders, reducing agents and colouring agents. (ORACLE, 2011) When fireworks explode, they produce sound, light and heat. Light is produced because when the colouring agent (a metal/salt) is heated, the atoms of each element take in the energy and then emit it as different coloured light. The colour of the fireworks depends on the length of the waves emitted from the compound, with different elements emitting different wavelengths. (John A. Conkling, 1985) (Rebecca H, 2013) Only the colouring agent is relevant in terms of the colour of fireworks.

A Wavelength is the length of a period in a wave, and a wave is energy that moves through a medium. (Conjecture Corporation, 2013 ) There is a large range of different wavelengths of light; this range is known as the electromagnetic spectrum. (Conjecture Corporation, 2013)

Frequency is defined as ‘the number of periods or regularly occurring events of any given kind in unit of time, usually in one second’ (Dictionary.com, 2012). Frequency is equal to the speed a wave is travelling divided by the length of that wave. (Davison E. Soper, 2007 ) Frequency can be used to find the length of the wave and energy.

Planks theory (E=hv) explains the relationship between light and energy, where E stands for energy, v stands for frequency and h stands for planks constant which is 6.626*10^-34 (F Scullion, 2013)

White light is the colour seen by humans when all the different colours are combined (white). When white light is shone through a prism, it separates the light into separate colours. (Conjecture Corporation, 2013)

If white light is shone on a material, that material will absorb some of that light, and then emit the rest. The wavelengths emitted make up the colour that we see. If something is black, that means that it absorbs all the wavelengths and does not emit any. When heated, chemicals emit different wavelengths showing particular colours (refer to Abstract). Below is a table of the colour and wavelength emitted from different compounds (refer to appendix A). The compounds in this table would be used as the colouring agents mentioned before, to make the fireworks a particular colour.

The wavelength of light can be determined from its frequency. The worked example from the chemistry textbook was used for an example of a problem where the wavelength was found, given the frequency. (Prentice Hall Chemistry) Anthony C. Wilbraham, Dennis D. Staley, Michael S. Matta, Edward L. Waterman) What is the wavelength of the yellow sodium emission, which has a frequency of ? Solution:

The frequency and wavelength related by the formula you rearrange to In which c = speed of light (). Then substitute:

The following is an explanation of what the above example was doing and why: First, the formula was used, in this formula, , and . This was needed to be rearranged due to the variables given, is the variable that is missing so it goes on its own. Then substitute the values for c & v into the new equation and work it out using a calculator. The answer is in m so convert to nm. This could be used to find the frequency as well by rearranging the original equation so v is on its own. This is useful because if you combine the formula it with the table giving the frequencies of different colours, it allows you to find the frequency given a certain coloured fireworks, or vice versa (range of frequencies).

So, when fireworks go off, the colouring agent absorbs photons from the explosion, causing electrons to jump up an energy level, then, when they return back down, the agent emits light, the colour and wavelength depending on what compound the colouring agent was made out of.

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