Flame Test Lab Introduction
By placing a metal sample into a flame, the electrons in the metal atoms can be induced to absorb
energy and jump to an excited energy state, a “quantum jump.” They then return to their ground state by
emitting a photon of light. The law of conservation of energy indicates that the photon emitted will
contain the same amount of energy as that absorbed in the quantum jump. The amount of energy in the
photon determines its color; red for the lowest energy, longest wavelength light, and then increasing in
energy through the rainbow of orange, yellow, green, blue, indigo, and finally violet for the highest
energy, shortest wavelength light. Photons outside the visible spectrum (which are part of the much
broader electromagnetic spectrum) may also be emitted, but we cannot see them.
The arrangement of electrons in an atom determines the size of the quantum jumps. The size of
the quantum jump dictates the energy and colors of the photons emitted. Since the electrons can jump to
a finite number of levels in an atom, only a relatively few quantum jumps are possible. Therefore, only a
few different colored photons are emitted as electrons move from an excited state back to the ground
state. This collection of photons is known as the atom’s emission spectrum.
Each element has a unique emission spectrum which can serve as a ‘fingerprint’ of the element.
We can view the emission spectrum of colors all at once with the naked eye. It will appear to be one
color, which you will carefully describe. It is also possible to view the separate colors of the emission
spectrum by using a spectroscope, which acts like a prism by refracting light depending on its
wavelength. Low energy, long wavelength light (red) bends the most and high energy, short wavelength
(violet) bends the least. This allows us to see the various distinct colors in an emission spectrum of an
element as separate lines.
In this lab, you will examine the line emission spectrum for seven different elements and predict
the color of the flame produced by those metals when a small sample is placed in a flame. After making
your prediction, you will record the flame test color after placing a q-tip soaked in a saturated solution of
the metal ion into a flame.
Finally, you will examine the line emission spectrum for five elements in the gaseous state. You
will be expected to draw and label the spectrum and calculate the energy associated with the highest and
lowest energy photons emitted by those elements.
Purpose:
To determine the emission spectrum of various elements using a flame test technique and
observe the line emission spectrum of five elements.
Flame Test Colors
COMPOUND METAL COLOR PREDICTION/Explanation
SYMBOL
potassium
copper
boron
strontium
calcium
lithium
sodium
Unknown 1
Unknown 2
COLOR OBSERVED
Calculations:
1) Pick one of the metals and find the line emission spectrum for that metal on-line. Metal: __________
a. Identify the wavelength of the lowest energy transition visible in the line emission
spectrum for this metal.
b. Calculate the frequency of the photon emitted when an electron makes the transition you
identified in a.
c. Calculate the energy of the photon you identified in b.
Conclusions
1) Compare the flame test color and emission spectrum for CaCl2, BaCl2, and SrCl2. All three
compounds contain chloride ions (Cl). Is there a difference between the flame color and emission
spectrum for the three compounds? Explain your answer.
2) You conduct a flame test on several unknown metals and observed that they were all shades of
red. Can you identify the metal? If not, what additional experiment would you propose to identify
the metal?
3) During a flood, the labels from three bottles of chemicals were lost. The three unlabeled bottles
contain white solids. You know the three bottles contained strontium nitrate, ammonium
carbonate, and potassium sulfate. Explain how you could easily test the substances and relabel the
bottles.
Examining the Line Emission Spectrum of Gaseous Elements
There are four stations set up for you to view the line emission spectrum of gaseous elements.
At each station, there is a spectroscope for you to examine the line emission spectrum in detail.
Compare the line emission spectrum you observe with the line emission spectrum from the power point
discussed in class. Can you relate the bulb color to the line emission spectrum for each gas?
Atomic Line Emission Spectrum for Gaseous Elements
Element Name: _________________________ Color observed: _______________________________
Relate color observed to line emission spectrum:
Element Name:_________________________
Relate color observed to line emission spectrum:
Color observed: ___________________________
Element Name: __________________________
Relate color observed to line emission spectrum:
Color Observed: ______________________