Atomic Spectra/Flame Test Practical
Part A Results: The Flame Test
Salt
NaCl
KCl
BaCl
FeCl
MgCl
CuCl
SrCl
LiCl
Unknown A
Unknown B
Colour
Orange
Violet
Green
Orange
Blue
Green
Red
Red/Pink
Orange
Green
Intensity
Strong
Medium
Light
Light
Light
Strong
Very Strong
Strong
Strong
Light
Part B Results: The Emission Spectrum of Hydrogen
Wavelength
Colour
4500
Blue
5500
Green
6000
Orange
6500
Red
Missing
Discussion:
In Part A, a sample of known metal salts were excited using a Bunsen flame to determine the
different colours and intensities emitted by the electrons. The observations allowed the
identification of two unknown salts by comparing their characteristics with those of the known
sample. Unknown A produced a strong orange light which aligned with the test for NaCl.
Unknown B produced a green coloured result of low intensity which aligned with the results of
the metal salt BaCl. Unknown A is therefore NaCl, and unknown B is BaCl.
From viewing the observations noted about intensity we can see that, in general, the lower the
wavelength of the light, then the stronger the intensity observed. This may only be a
coincidence, however the position of the colour on the continuous spectrum seems to relate to
how strong the colouring is. An example is that SrCl was the most intense colour and red is at
the highest wavelength. SrC was also excited to the highest energy level to begin with, and
therefore had more energy to lose.
In Part B, we can see the different lines that were shown on the spectrometer for the hydrogen
emission spectra. However, these values calculated do not match the official values given for
the element of hydrogen. Part B shows that as the wave length increases, the electrons are
more easily excited and therefore the colours move toward emitting reds or oranges. In
contrast, with the wavelength of 4500 shown, a blue was emitted which is towards the lower
end of the colour spectrum.
Evaluation:
This experiment is not particularly reliable as no repeat tests were conducted. Also, Part A
depended solely on our own observational skills which also decreased the accuracy of the
results. Part B was more scientific and reliable, as proper scientific equipment was used to
measure the results. However, I did not get a chance to calibrate the spectrometer against the
violet or green lines, meaning that the values I recorded at the end were not at the exact
wavelength that they should have been when looking at the official data. If I were to complete
this experiment again, there were many improvements that could have been made. One
improvement would have been to conduct more tests in Part A to ensure that all results were
true and accurate, whereas another would be to use more scientific equipment if possible
rather than relying on our own opinions. Two good design points of this experiment are that it
was relatively simple to discuss and was quite suitable for our ability level, while you could also
through this method see the colours produced very easily. Overall, the validity of the method
was good however as there was no hypothesis for this investigation A further idea that could
be investigated within the same topic is to look at the line spectrums for other elements, which
may be more complex. In relation to the flame test, you could see whether any other elements
produced colours.
Conclusion:
In conclusion, the colours produced through flame tests are the result of initial excitation of
electrons to higher levels followed by a decrease to lower energy levels. When this occurs,
energy is emitted in the form of light. This is only the case with some elements, for example the
alkali metal cations and some other metal cations, as the emission is in the visible region of the
electromagnetic spectrum and appears as a characteristic colour.
Marks