Name_________________________________
Flame Test for Metals Lab
Purpose
To observe and identify metallic ions using flame tests.
Background
By placing atoms of a metal into a flame, electrons 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 visible light, increasing energy through the rainbow of orange yellow green blue indigo, and finally
violet for the highest energy visible light. Photons outside the visible spectrum may also be emitted, but we
cannot see them.
The arrangement of electrons in an atom determines the sizes of the quantum jumps, and thus the energy and
colors of the collection of photons emitted, known as emission spectrum. In this way the emission spectrum
serves as a ‘fingerprint’ of the element to which the atoms belong. We can view the emission spectrum of
colors all at once with the naked eye. It will appear to be one color, which we will carefully describe.
Cobalt blue glass filters are often used when viewing solutions of metals that produce yellow light. Yellow light
is right in the middle of the visible spectrum. Colors at the edge of the visible spectrum, such as violet are more
difficult to see. Cobalt blue glass absorbs light at yellow wavelengths. But it is transparent to light of higher
energy (this is why it looks blue). Viewing the flame through cobalt blue glass will allow us to see if there is
any higher energy light present.
SAFETY
Avoid skin contact with all chemicals used in this experiment.
Wear safety goggles at all times while in the laboratory.
Use care when using the gas Bunsen burner. All long hair should be tied back!!!!
Dispose of all materials following instructions from the instructor.
Procedure
1. Dip wooden splint into labeled salt solution.
2. Hold wet wooden splint in flame; do not let it burn.
DO NOT DIP WOOD SPLINT INTO MORE THAN ONE SOLUTION
3. Record your observations; repeat for all available salt solutions.
(Note: View the flame colors produced by the Na and K salts with and without cobalt blue glass; record your
observations.)
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Observations
Use the “proper” names (i.e., red, orange, yellow, green blue, indigo, violet) when describing each flame
color. Feel free to use a hyphenated color name if it appears to be a blend of two adjacent colors.
Element
Flame Color
Sodium
Potassium
Calcium
Strontium
Lithium
Copper
Sodium with Cobalt Glass
Potassium with Cobalt Glass
Post Lab Questions
1. What color flame was emitted and observed by your eye when you used the cobalt-blue glass? What color is
responsible for hiding the hard to see colors?
2a. Determine the approximate frequency (Hz or s-1) for the color emitted by the excitation of copper atoms.
2b. Calculate the energy associated with the same color from 2a (honors only).
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