Flame Test Experiment

by kamranbadboyhotmailcom (student)

Flame Test

Flame tests are used to identify the presence of a specific metal within a substance. Metals change the colour of a flame when they are heated, different metals give different colors.

Flame tests are useful for confirming the results of a precipitate test. For example, an unknown solution that produced a pale blue precipitate with sodium hydroxide solution, and a green-blue flame test, must contain a copper compound. The test helps confirm which Metal it is.

To identify an alkali metal, a flame test must be used instead of a sodium hydroxide precipitate test. This is because the alkali metals do not form precipitates with sodium hydroxide.

Science behind flame tests

By providing heat energy (flame) to the substance, the electrons within the substance gain a higher energy level from ground state energy; this is due to the heat which is provided. As the energy increases the electrons become unstable and begin to move around more, when the electrons move back to state energy the energy taken in is given out within specific wavelength which gives out different colours. Depending on the substance, the colours of the flame vary which is then measured using the emission spectrum.

Apparatus

Goggles
Splints dipped in metal salts
Matches
Bunsen Burner
Safety (heatproof) Mat

Risk assessment

Method

This is a preview of the whole essay

Method

Before stating the experiment I would first start off by preparing a results table for my experiment, then I would take safety precautions such as wearing goggles. After the safety precautions I would then setup my equipment carefully. After setting up my equipment I will then be ready to start the experiment. To start my I would then light up the Bunsen burner using the matches, when I am finished with my matches I would then make sure that the fire on the match has gone out. After that I would turn the flame on the Bunsen burner to blue, this is done to stop confusion about the colour therefore the metal present in the salt/splint. Then I would get the different splints and hold them on the flame this will cause a change in the colour. I would record the results on a table that I will have drawn out. I would then repeat the experiment with different splints. The splints contain the following metal salts:

Calcium Carbonate
Potassium Chloride
Sodium Chloride
Copper Carbonate

In the experiment the dependent variable is the colour of the flame.
The independent variable is the different splints.

Hypothesis

If I change the wooden splints, which contain different salts of metals, this will cause a change in colour of the flame when I slightly burn the splint.

Results

Conclusion

My hypothesis was correct it was relevant to my results after the experiment. When you burn different metal salts they will give you different flame colour. During my experiment I found out that when you burn Copper Carbonate it will give you blue/green colours. I did the experiment very well because my results were correct and according to the original colours. For example Ca is red. Overall the experiment had given me relevant results which I then was able to see if they were correct, the experiment is quick, easy and cheap. During the experiment my aim was achieved which was to try and identify the unknown substances present in the sample. When I put unknown A in the flame it turned yellow from this I could tell it was Sodium, I had confirmed this when I had looked at the internet webpage. This helped me identify unknown A, when I did the same for B I got the colour pink/ lilac, from this I could tell that substance B was Potassium.

Evaluation

Flame tests are used to identify the presence of a specific metal within a substance. Flame test can be used quickly and easily. Flame tests are very cost effective and are very efficient.

Limitations of the flame tests are that it cannot detect low concentrations of most ions. Some compounds do not change the colour of the flame at all. The brightness of the colour varies so there could be a mix up between the colours.

During my test I found out that I had an anomaly which was potassium which gave me an orange colour which wasn’t correct compared to other results. To fix this anomalous result I would repeat the experiment again doing only the potassium to see if this can get fixed. I would do this to get more reliable results. This anomaly may have been caused by many different reasons, this may be because I may have used the wrong splint or the metal was contaminated. To fix this result I would repeat my experiment again to get accurate results.

Limitations of a flame test

The first limitation of the test is that the test cannot detect low concentrations of most ions.
The brightness of the flame varies for example the colour of barium is pale green whilst the colour of copper is green/blue as well which means that it will be hard to tell which metal the colour of test represents.
There could be another metal mixed in with the mixture/solution. A compound is an example and this could result in the change of the colour.
Some compounds do not change the colour of the flame