Name: ______________________________________
Date: _______________
Flame Test Lab
Chemists began studying colored flames in the 18th century and soon used "flame tests"
to distinguish between some elements. Different elements burn with different colored flames.
Although some of the flames you will be seeing will appear similar in color, their light can be
resolved (separated) with a prism into distinctly different bands of colors on the electromagnetic
spectrum (ROYGBIV). These bands of colors are called atomic line spectra, and they are
UNIQUE to each element.
Violet indigo
blue
green
yellow
orange
red
Niels Bohr studied the line spectrum for hydrogen, and wondered what the specific line
spectrum had to do with the structure of the atom. He postulated that an electron can have only
specific energy values in an atom, which are called energy levels. Bohr believed that the
energy levels for electrons were quantized, meaning that only certain, specific energy levels
were possible. Also, the further away from the nucleus, the more energy the electrons have.
How does an electron move between energy levels? By gaining the right amount of
energy, an electron can move, or undergo a transition, from one energy level to the next. We
can explain the emission of the light by atoms to give the line spectrum like this:
1. An electron in a high energy level (excited state) undergoes a transition to a low energy level
(ground
state).
The transition is instantaneous & complete.
2. In this process, the electron loses energy, which is emitted as a photon of light (a particle
which
behaves like a wave)
3. The energy difference between the high energy level and the low energy level is related to
the
frequency (color) of the emitted light.
Pre-Lab Questions:
1. Bohr's important discovery was that energy levels of electrons are quantized (only existing in
certain,
specific levels). In what year was this discovery made?
2. What happens to an electron when energy is added?
3. What is released when an electron loses energy?
4. What determines the frequency (color) of photons?
The Flame Test
Objective: To identify atoms in solutions using the colors they emit when heated.
Safety:
1. Follow all lab safety rules.
2. Place only the wire loop in the flame.
3. Wear apron and safety goggles at all times.
4. Do not knock over the flame, reach over it, or clutter your lab area with paper
Instructions for flame tests:
1. You are going to find out what color flame six different known samples make. Then, you will
use
your results to determine which metal is in the “unknown” sample.
2. Clean the metal loop in the hottest part of the flame. Be sure not to cross-contaminate the
samples.
3. Dip the wire loop in the solution and hold it over the flame. Observe and record the color.
4. Once you have collected your data for the “known” samples, test your unknown solution.
Record the
unknown sample number, color and element in the data table.
Solution
Strontium
Calcium
Lithium
Sodium
Copper
Potassium
Unknown #____
Color of Flame
Which atom is it?
Sr2+
Ca2+
Li+
Na+
Cu2+
K+
Post Lab Questions:
1. Why do atoms give off light energy when heated? (Use “electrons” somewhere in your
answer.)
2. Explain what could happen if the wire is not properly cleaned?
3. Explain why different atoms give off different colors of light?
4. Write the isotopic notation, Lewis dot structure, and the electron configuration for all the
elements tested (except copper) on the back of this page.
5. Is the change observed in this lab a physical change or a chemical change? Explain your
answer.
6. Why do you think that we used the metal salts instead of the pure metals? (Think about the
properties of the pure elements)
What do the street lamp, salt, and fireworks have in
common?
They all contain SODIUM, which gives off a unique
ORANGE flame when heated.
You are going to find out what color FLAME six different known samples make. You will then
use your results to work out which metal is in the unknown sample.
Your first Job is to make sure that your flame test wire is CLEAN. Do this by holding
the metal loop in the hottest part of the Bunsen burner
flame. If
it is clean there should be no change in the color of the
flame
when the metal loop is put into the flame.
If the metal loop is NOT CLEAN, clean it by dipping it into
the HCl
solution provided then holding it in the burner flame until
there is
no change in the color of the flame. You should have different loops for each
sample. DO NOT cross contaminate samples by using different loops then the ones
assigned to the sample.
Your next job is to do the flame tests. Dip the wire loop into one of the known
solutions. Then hold the metal loop in the hottest part of the Bunsen burner flame.
Make a note of the color in the FLAME TEST CHART.
Continue to test the other known solutions. Keep going until you have recorded the
color of al of the known solutions.
Repeat job 2 but use the unknown solution. Can you figure out what metal is in
this solution(don’t forget to record the sample # in your chart)
Post-Lab Question #4:
Element
Example:
Nitrogen
Isotopic Notation
Calcium
Lithium
Sodium
Potassium
Electron Configuration
14
7
Strontium
Lewis Dot Structure
N
1s22s22p3
1.