2. Literature Review

Keywords : Chemicals, fire, atoms, protons, neutrons, electrons, photons, flame photometry, ions, metals, non-metals, spectral lines, atomic spectroscopy.



What is copper sulfate?
Copper sulfate is an inorganic compound that combines sulfur with copper. It can kill bacteria, algae, roots, plants, snails, and fungi. The toxicity of copper sulfate depends on the copper content. Copper is an essential mineral. It can be found in the environment, foods, and water.

How does copper sulfate work?
Copper in copper sulfate binds to proteins in fungi and algae. This damages the cells causing them to leak and die. It also disrupts the normal function of the skin cells and enzymes.

What is strontium chloride?
Strontium chloride is a mixture of strontium and chloride creating a salt. It is also like a typical salt which can form neutral aqueous solutions. Strontium chloride is often used as a red colouring agent in pyrotechnics It imparts a much more intense red colour to the flames than most other alternatives.

What is boric acid?
Boric acid, also known as boracic acid or orthoboric acid, is naturally occurring compound containing the elements boron, oxygen, and hydrogen (H3BO3). In nature, the element boron does not exist by itself. Boron is combined with other common elements, such as sodium to make salts like borax and with oxygen to make boric acid. Boron is considered to be essential micronutrient for plants and perhaps humans. Boron in the diet most commonly comes from the boric acid naturally present in most foods. Fruits, vegetables, grains, and nuts are particularly high in boron. In fact, the average person eats between one to three milligrams of boron each day as part of a normal healthy diet. Boric acid also occurs naturally in water and soil.

How does atoms affect the colour of flames?
Pharmaceuticals and Cosmetics: boric acid is a mild antiseptic as well as a mild acid that inhibits
the growth of microorganisms on the external surfaces of the body. It is commonly used in
contact lens solutions, eye disinfectants, baby powder, anti-aging preparations and similar external applications.

Based on the information by (Stephen Reucroft), being left on their own, the electrons of an atom tend to relax into orbitals that leave the atom with the lowest possible energy--its ground state. Putting atoms into a flame, though, adds energy to the looser electrons farthest from the nucleus and pushes them into other orbitals. Eventually, these excited electrons drop back to where they ought to be, and in so doing, they release the energy they stored up as particles of light, called photons.The color of the light emitted depends on the energies of the photons emitted, which are in turn are determined by the energies required to move electrons from one orbital to another. A flame has lots of different energies existing within it all the time, and every so often, it gets lucky and has the right quantity present to push an electron from one orbital to another. When the electron drops back, it must release the same exact amount energy that it absorbed. Depending on the element you put in the flame, various different energies of photons (colors) will appear.

What is flame spectrometry and how is it used by physicists and chemists?
Based on a research by (Professor H.Y. Aboul-Enein), it is the analytical technique that measures the concentration of chemical elements in a sample. When elements are transformed into atomic vapour at high temperatures, emission or absorption of light may occur and this can be accurately measured at a unique resonant wavelength, which is characteristic of the emission/ absorption lines of the elements concerned.

Using this basic process, the concentrations of most elements may be estimated by measuring the amount of radiation either emitted by the sample (emission spectrometry) or absorbed by the sample following production by a primary radiation source (absorption spectrometry).
In emission spectrometry/flame photometry, a small proportion of the atoms undergo excitation with a subsequent and characteristic emission of radiation, at wavelengths in the ultraviolet or visible regions, which is proportional to the number of excited atoms.
Thus under controlled conditions, it is possible with either technique to relate the measured light intensity (emission or absorption) to the concentration of individual elements in the sample.
The major advantage of emission spectrometry is the relatively low cost and simplicity of instrumentation, since it requires no additional source of primary radiation. The fraction of excited atoms produced by most elements at normal flame temperatures is small and hence, in practice, emission spectrometry is limited to a few elements such as sodium, potassium, lithium, and calcium. Sensitivity may be increased, however, by using higher flame temperatures or other more effective means of excitation.

In comparison, absorption spectrometry offers greater sensitivity, since absorption is proportional to the concentration of ground state atoms, which are produced in sufficient numbers by most elements at normal operating flame temperatures. The disadvantage of this technique is the high initial cost of instrumentation, because of the requirement for a primary source of radiation (an individual hollow cathode lamp, one for each element to be determined).
Both techniques are comparative in nature and require the concomitant preparation and use of standard reference solutions of all elements to be determined.

The emission spectrometer consists essentially of a burner - an atomic generator of the element to be determined (flame, furnace, plasma, arc, etc.), a suitable filter or monochromator, and a detector. The absorption spectrometer also includes a source of radiation (a hollow cathode tube) where the cathode consists of the same element as that to be determined.

Use of solvents
For flame spectrometry, the ideal solvent is one that produces neutral atoms and interferes the least with the emission or absorption processes. Differences in surface tension or viscosity between the test and reference solutions may cause difficulties in the aspiration or atomization rates and significant changes in the signals generated. The solvent of choice for the preparation of test and reference solutions should, therefore, be water, although organic solvents, such as flammable solvents, either alone or mixed with water, may also be used if precautions are taken to ensure that they do not interfere with the stability of the flame. When mineral acids are necessary for the dissolution of the element, care should be taken to avoid interference from the acidic anion. A dilute solution of hydrochloric acid is the preferred solvent for this purpose.

To calibrate the instrument, introduce water or the blank solution into the atomic vapour generator (flame) and adjust the reading of the instrument, either to zero foremission spectrometers or to indicate maximum transmission for absorption spectrometers. For emission measurements, introduce the most concentrated standard solution into the flame and adjust the sensitivity to full-scale deflection. Refer to the manufacturer's instructions for instruments with an absorbance scale.

How does this science project relate to what astronomers do when they are trying to identify the atomic makeup of a star?
It is related as astronomical spectroscopy is part of atomic spectrometry like flame spectrometry which is the technique of spectroscopy used in astronomy. The object of study is the spectrum of electromagnetic radiation, including visible light, which radiates from stars and other hot celestial objects. Spectroscopy can be used to derive many properties of distant stars and galaxies, such as their chemical composition, temperature, density, mass, distance, luminosity, and relative motion using Doppler shift measurements.

Based on a research by Douma, flame tests are useful because gas excitations produce a signature line emission spectrum for an element. In comparison, incandescence produces a continuous band of light with a peak dependent on the temperature of the hot object.

When the atoms of a gas or vapor are excited, for instance by heating or by applying an electrical field, their electrons are able to move from their ground state to higher energy levels. As they return to their ground state, following clearly defined paths according to quantam probabilities, they emit photons of very specific energy. This energy corresponds to particular wavelengths of light and so produces particular colours of light. Each element has a 'fingerprint' in terms of its line emission spectrum.

Based on an essay by (Tega), it says that depending on the kind light an element burns scientist can analyze a star’s light and basically determine its elemental composition. The most important factor to a star’s color has to be its surface temperature. If you have ever seen an open flame you would understand why. A blue flame is flame burning at very high temperatures. A yellow flame has temperatures that are cooler than blue flames and red flames are the coolest of all. The same thing happens with stars. Very hot stars tend to be blue stars. Stars with an average surface temperature become yellow stars like our sun.

As each element has an exactly defined line emission spectrum, scientists are able to identify them by the colour of flame they produce.

Bibliography :

Astronomical spectroscopy - Wikipedia, the free encyclopedia. (n.d.). Retrieved August 16, 2013, from https://en.wikipedia.org/wiki/Astronomical_spectroscopy

Copper Sulfate General Fact Sheet. (n.d.). Retrieved July 10, 2013, from http://npic.orst.edu/factsheets/cuso4gen.html

Flame tests | Causes of Color. (n.d.). Retrieved July 16, 2013, from http://www.webexhibits.org/causesofcolor/3BA.html

Jessa, T. (2010, October 15). Why Are Stars Different Colors. Retrieved July 31, 2013, from http://www.universetoday.com/75839/why-are-stars-different-colors/

Reucroft, S., & Swain, J. (n.d.). Why do certain elements change color over a flame?: Scientific American. Retrieved July 9, 2013, from http://www.scientificamerican.com/article.cfm?id=why-do-certain-elements-c

Rose Mill Company (2008). What is Boric Acid. Retrieved July 9, 2013, from http://www.natbat.com/What%20Is%20Boric%20Acid.pdf

Strontium chloride - Wikipedia, the free encyclopedia. (n.d.). Retrieved July 10, 2013, from http://en.wikipedia.org/wiki/Strontium_chloride

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