Why do we see colors in a flame test?
The electrons in an atom occupy different energy levels,
as you know. When all of the electrons are at the lowest
possible energy level they are said to be in the ground
state. Electrons do not always stay in the ground state.
Sometimes they can be promoted to a higher-energy
electron shell. When an atom is in the flame, an electron
in the outer shell of that atom receives energy from the
flame and jumps up to a higher-energy shell position.
When an electron is in a higher-energy shell it is said to
be in an excited state.
Electrons in excited states do not usually stay in them for
very long. When electrons lose their energy they do so by
emitting a photon of light. Photons are particles with
energy but no mass. Their energy is directly proportional
to the frequency of the light. The photons emitted
precisely match the quantum energy difference between
the excited state and the ground state.
Is the flame test fun? Yes!!!! But… what is/was a flame test used for?
The light produced by very hot atoms in the gaseous state is a unique spectrum for each element. To observe the
spectrum requires the use of a prism, diffraction grating, or spectroscope. (We will look at line spectrum of various
elements using a spectroscope next week.) However, before complex instruments were invented, to observe elemental
spectra chemists sometimes identified metals in compounds by doing a flame test.
Further explanation of the flame test:
Salts are a type of compound that include a metal and a non-metal. Sodium chloride (NaCl) is the most familiar example
of a salt but others include calcium chloride(CaCl2) and copper(II) chloride (CuCl2). In flame tests, salts that are dissolved
in water are evaporated using a hot flame. In the flame, the metal atoms become excited and produce their
characteristic spectrum of light. However, since the observer does not use a spectroscope only one color is observed.
Many metals produce a unique single color under these conditions, while other metals produce very similar colors that
only practiced eye can distinguish. An experienced scientist, based on a comparison between the color observed and the
known colors produced by different metallic salts can identify the salt. We will try our ability to identify an unknown salt
during the flame test lab.
Real world use:
This ability of metal atoms to produce these colors is put to use in the making of fireworks. By including different metal
salts, or mixtures of metal salts, in the exploding shell of a firework, firework manufactures can produce beautiful
displays in nearly all the colors of the rainbow.
Optional: If you are interested in learning more about the chemistry of fireworks refer to the below sites. (Use the
document posted on our website for active links.
 NOVA from WGBH: Fireworks! (http://www.pbs.org/wgbh/nova/fireworks/)
 Chemical of the Week: Fireworks! from the University of Wisconsin
(http://www.scifun.org/CHEMWEEK/fireworks/fireworks.htm)
 A Chemical and Engineering News article about Fireworks
(http://pubs.acs.org/cen/whatstuff/stuff/7927sci3.html)
Limitations of the Flame Test
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The test cannot detect low concentrations of most ions.
The brightness of the signal varies from one sample to another. For example, the yellow emission from sodium is
much brighter than the red emission from the same amount of lithium.
Impurities or contaminants affect the test results. Sodium, in particular, is present in most compounds and will
color the flame. Sometimes a cobalt glass is used to filter out the yellow of sodium.
The test cannot differentiate between all elements. Several metals produce the same flame color. Some
compounds do not change the color of the flame at all
Flame Test Colors:
Symbol Element
Color
Mg
As
Arsenic
Blue
Mn(II) Manganese(II)
Yellowish green
B
Boron
Bright green
Mo
Molybdenum
Yellowish green
Ba
Barium
Pale/Yellowish Green
Na
Sodium
Intense yellow
Ca
Calcium
Orange to red
P
Phosphorus
Pale bluish green
Cs
Cesium
Blue
Pb
Lead
Blue
Cu(I
Copper(I)
Blue
Rb
Rubidium
Red to purple-red
Cu(II)
Copper(II) nonhalide
Green
Sb
Antimony
Pale green
Se
Selenium
Azure blue
Cu(II)
Copper(II) halide
Blue-green
Sr
Strontium
Crimson
Fe
Iron
Gold
Te
Tellurium
Pale green
In
Indium
Blue
Tl
Thallium
Pure green
K
Potassium
Lilac to red
Zn
Zinc
Li
Lithium
Magenta to carmine
Bluish green to whitish
green
Symbol Element
Color
Magnesium
Bright white