Below are my group's observations of the colours of the flame when different elements were used:
Barium - Yellow
Calcium - Red-Orange
Copper - Green
Lead - White-Pink
Potassium - Pinkish-Orange
Sodium - Orange-Yellow
And here are the answers provided by Ms Tan as to what the colours should be:
Barium - Pale/Yellow-Green
Calcium - Orange-Red
Copper - Blue-Green
Lead - White/Blue
Potassium - Lilac to Red
Sodium - Intense Yellow
Magnesium - Bright White
Possible reasons for the differences could be due to:
- The contamination of the bunsen burner, where other elements could have dropped into the bunsen burner, causing the flame colour to change
- My group's perception of the colour of the flame could have been different
QUESTIONS and ANSWERS
1. How and what is it (flame test) used for in "crime scene investigations/forensic science"?
They are used to identify different elements found in a sample collected at a crime scene. Since the sizes of the possible jumps in energy terms vary from one metal ion to another when heated, different ions will have a different pattern of spectral lines, and so different flame colours. These different flame colours are used to identify elements. The flame colours of the elements in the sample collected at the crime scene can then be compared to the known colours of different elements, thus identifying the elements found in the sample and narrowing the search for the culprit.
2. If there are more than one trace metal present, is the flame test still a suitable technique to identify the trace metals?
No. There would be a mix of colours, making it difficult to identify the different elements. We would be unable to tell if the colour was produced as a combination of colours produced by different elements (e.g. Sodium that is yellow combined with Lead that can be white or blue may produce a green flame)
3. Is a flame test sufficient to identify the trace metal(s) present?
Although it may help to narrow down the spectrum of elements involved, it is not sufficient to identify the trace metals present solely based on a flame test. This is because some elements produce highly similar colours and others do not change the colour of the flame. Furthermore, the colour of the flame produced by the trace element is subject to our perception, making it very relative and not completely accurate.
4. What is a "Mass Spectrometer"?
The mass spectrometer is an instrument which can measure the masses and relative concentrations of atoms and molecules. It makes use of the basic magnetic force on a moving charged particle.
In order to measure the characteristics of individual molecules, a mass spectrometer converts them to ions so that they can be moved about and manipulated by external electric and magnetic fields. The three essential functions of a mass spectrometer, and the associated components, are:
1. A small sample is ionized, usually to cations by loss of an electron. The Ion Source
2. The ions are sorted and separated according to their mass and charge. The Mass Analyzer
3. The separated ions are then measured, and the results displayed on a chart. The Detector
This website is very useful for understanding the basic principle behind the mass spectrometer as well as how it works: http://www.chemguide.co.uk/analysis/masspec/howitworks.html
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