Flame Test Lab
Objective
In this lab students will learn about atomic energy levels, emission spectroscopy, and
flame tests for element identification.
Overview
Students will use small samples of 6 chloride salts of different metals. These they will
place into a flame in order to observe the colors produced. These colors come from the
excitation of electrons which then resume their ground states by emitting light of very
specific colors.
Background
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.
This can happen in two
ways. First, the electron can
absorb a photon of just the
right amount of energy to
move it from one quantum
shell to another. Second,
when atoms are heated or energized with electricity their electrons can gain energy. This
promotes them to the higher-energy shell. 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
(remember: E = hf). The photons emitted precisely match the quantum energy difference
between the excited state and the ground state.
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. Before complex instruments were invented to observe elemental spectra
chemists sometimes identified metals in compounds by doing a 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
