Download 7.3-Flame Test Lab

Flame Test Lab
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Introduction
All metal elements have distinct properties. One of these properties is its own special color when burned in an
open flame. This is caused by the flame exciting the electrons of the metal element in a compound. When the
electrons return from the excited state to the ground state, a photon of energy is released. Some of the energy is
in our visible light spectrum, and therefore we can observe the different colors of the different metals. (The
finger prints of metals) Only the metal in the compound is affected by the flame.
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, and finally violet for
the highest energy visible light. Photons outside the visible spectrum may also be emitted, but we cannot see
them (ie: infrared or ultraviolet EM waves).
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. It is also
possible to view the separate colors of the emission spectrum by using a spectroscope, which bends light of
different energies differently. Low energy red light is bent the least, and high energy violet the most. This
allows us to see the various distinct colors of the emission spectrum of a sample.
Finally, we will use the data we collect to identify a metal in an unknown salt solution. This process is the same
as that used by chemical laboratories to identify the make-up of chemical contamination in chemical spills,
landfills, industrial sites, etc. This must be done to determine the possible threat to human health and the
ecosystem due to contamination.
Purpose
To identify some metals by the color they emit when the electrons are excited by the flame.
Materials
 Goggles
 Bunsen burner
 Wooden stir-sticks
 Water
 7 ionic compounds
 1 Unknown compound
Procedure: In order to obtain reliable results, avoid cross-contamination by using a new wood splint for each
metal solution.
1.
2.
3.
4.
5.
Light your Bunsen burner and adjust it so you have a small blue cone.
Obtain a wood splint and dab it into one of the known metals. *Only a little is required.
Briefly place the wood splint in the flame.
Record the color of the flame in data table 1. Repeat for all 7 metals, getting a new splint each time.
Discard the wood splints in the trash when cool.
Identifying an Unknown
1. Repeat the procedure with the unknown test solution(s).
Name________________________________ Block__________ Date___________________
7.3-Flame Test Lab
Pre-Lab Questions
1. Complete the Formula and Name of Metal columns in the Data Table.
2. When electrons are excited and jump to an excited energy state, it is called a “
3. An emission spectrum is a “
the compound.
“ jump.
“ for the atom and helps us to identify the metal in
4. A spectroscope bends the light of different energies differently. Which color bends the most?
5. Which color is bent the least?
6. Write the main colors of the visible light spectrum in order from the longest wavelength to the shortest.
(You should have 6 colors)
7. Which is highest in energy?
8. Which color has the lowest frequency?
Data Table 1
Name of compound
Barium chloride
Calcium chloride
Copper (II) chloride
Lithium chloride
Potassium chloride
Sodium chloride
Strontium chloride
Unknown # _____
Formula
Name of Metal (cation)
Flame Test Color
Conclusion Questions
1. Which metal is contained in the unknown sample?
2. Most salts contain a metal and a non-metal. Look at the compounds we tested and determine how we
can be sure that it is the metal atoms that emit the light/photons and not the non-metal.
3. What color(s) would you expect to see for a sample of the following compounds: potassium
chloride, potassium nitrate, potassium sulfate?
4. Aerial fireworks contain gunpowder and chemicals that produce colors. What elements would you
include to produce the following colors?
Red:
Green:
Yellow:
5. If milk was boiling on a gas stove and it boiled over, what color would you expect to see? Explain.
http://www.kent.k12.wa.us/staff/carriewattles/chemistry/flametestlab_inst.htm
http://www.creative-chemistry.org.uk/activities/documents/flametests.pdf
http://74.125.113.132/search?q=cache:67WGZoMVx4cJ:teachers.sduhsd.k12.ca.us/jvaldivieso/Assignments/La
b_FlameTest_mod.doc+flame+tests+conclusion&cd=4&hl=en&ct=clnk&gl=us
https://www.msu.edu/~moorean4/TestSite/Chemistry%20Labs/Unit%204%20Labs/flametest.pdf