Flame Tests for
Ions
Flame Tests Using an
Improvised Alcohol
Burner
Purpose
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When a metal salt solution is
burned, the metal provides a
colored flame.
Each metal ion gives a different
colored flame.
Flame tests, therefore, can be
used to test for the absence or
presence of a metal ion
From the Demonstration
Procedure taken from: Dragojlovic, V. Flame tests using
improvised alcohol burners. Journal of Chemical Education
(76)7, 929.
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Metal salt
solutions in a
methanol solvent
were burned in
5mL vials with
paper wicks.
Two unknowns
were also tested.
Each solution
provided a
different colored
flame.
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Li
K
Ca
Na
Ba
Red
Violet
Orange
Yellow
Yellowgreen
Unknown A
Red
Unknown B
Yellow
Important Concepts
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Atomic Orbitals
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Energy States of Atoms
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Ions
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Atomic Emission
Atomic Orbitals
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Electrons of atoms reside in concentric
spheres known as energy “shells” in
which they orbit the nucleus of an atom.
Each shell is assigned a principal
quantum number, n.
The value of n is an integer, 1, 2, 3, etc.
This number determines the relative
energy of the orbital and relates the
distance from the shell to the nucleus--the lower the number, the lower the
energy of the electron and the closer it is
to the nucleus
Electrons can be further distinguished
according to their location in atomic
orbitals, specified regions in space that
depend on their energies
Energy States of
Electrons
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A ground state refers to the lowest
energy of system, in this case an
atom. All electrons are in shells with
the least energy.
As energy is applied to the atom, an
electron is promoted from its ground
state (residence in an energy shell) to
a higher energy shell or an excited
state.
The excited state has a higher n
value, has more energy, and is less
stable.
Atomic Emission
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An emission spectra is obtained by
adding energy to a material.
The addition of energy promotes
electrons of that material from the
ground state to the excited state.
As the electrons “fall” from the excited
state to the ground state, they emit the
energy they absorbed in the form of
electromagnetic radiation (heat, light,
etc.)
Ions
• Ions are charged atoms; we use metal
salts in this demonstration which contain
metal cations and some non-metal anion
• For example, sodium chloride has
neither sodium atoms nor chlorine atoms
in it…rather, it is made of sodium ions
Na+ and chloride ions, ClThe sodium ion is the cation and the
chloride ion is the anion
• Ions undergo atomic emission and give
characteristic colors
• This is a way to identify what ion might
be present
Conclusions
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Each metal provides a different
colored flame by which it may be
distinguished from other metals.
The color of the flame is caused by
the demotion of electrons from an
excited energy state to a ground
state.
Electrons fall from higher energy
states to lower energy states which
have smaller n values and are more
stable.
Comments
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Atomic emission is used in street lamps,
fluorescent lights, and neon signs.
Two common street lamps using this are
the mercury lamp and the sodium lamp.
“Neon” signs frequently implement the
emission spectra of other gases such as
argon and krypton.
Very sophisticated instrumental
techniques such as “flame photometry”
and “atomic absorption” are based on
the principles in this demonstration
Miniquiz on Flame Tests
True or False
1 The color of the first unknown was
red, therefore it was calcium.
2 The color of the second unknown
was yellow, therefore it was sodium.
3 When an electron “falls” it emits
energy in the form of electromagnetic
radiation.
4 The greater the n value, the higher
the energy, the more stable the
orbital.
5 The n value corresponds to the
principle quantum number.
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Answers
False. A red flame is
indicative of Li.
True.
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True.
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False. The higher
the n value, the less
stable the orbital.
True.