Flame Tests
Emily Ma, James Haber
Date Completed: November 23rd 2010
Date Due: November 24th 2010
Pre-lab:
The normal electron configuration of atoms or ions of an element is known as being in
the ground state. In this most stable energy state, all electrons are in the lowest energy
levels available. When atoms or ions in the ground state are heated to high
temperatures, some electrons may absorb enough energy to allow them to jump to
higher energy levels. The element is then said to be in the excited state. This excited
configuration is unstable and the electrons fall back to their normal positions of lower
energy. As the electrons return to their normal levels, the energy that was absorbed is
emitted in the form of electromagnetic energy. Some of this energy may be in the form
of visible light. The color of this light can be used as a means of identifying the elements
involved. Such crude analyses are known as flame tests. Only metals, with their loosely
held electrons, are excited in the flame of a laboratory burner. Thus, flame tests are
useful in the identification of metallic ions. Many metallic ions exhibit characteristic
colors when vaporized in the burner flame. In this experiment, characteristic colors of
several different metallic ions will be observed, and an unidentified ion will be identified
by means of its flame test.
Purpose/Aim/Objective:
The purpose of this lab is to observe the characteristics colors produced by certain
metallic ions when vaporized in a flame. Identify an unknown metallic ion by means of
its flame test.
Equipment/Materials:
See Lab
Safety:
-
Always wear goggles during this lab
-
Wash your hands after the lab
-
Don’t eat any of the materials
-
Tie back long hair and tuck in loose clothing
-
Handle concentrated chemicals with care
Procedure:
1.
Take out all the needed materials
2.
Put on goggles for safety purposes
3.
Tie back hair; tuck in clothes if needed
4.
Place eight clean tubes into a test tube rack
5.
Into the first seven tubes, pour 5 mL of a different nitrate solution; pour 5 mL of the
unknown solution into the eighth tube
6.
Pour about 10 mL of concentrated hydrochloric acid into a 50 mL beaker
7.
Clean the wire loop by dipping the loop into the acid and heating the loop in the outer
edge of the burner flame until no color is observed in the flame
8.
Dip the clean wire loop into one of the nitrate solutions by placing the loop in the outer
edge of the burner flame and moving the loop up and down
9.
Note the color of the flame and record it
10. Repeat steps 7,8,9 for the other nitrate solutions and the unknown and record it
11. Clean up after yourself
Observations/Data:
Metallic Ion
Color in Flame
Na+
Bright Orange
K+
Light pink/ purple
Li+
Red
Ca2+
Red-orange
Sr2+
Red
Ba2+
Yellow green
Cu2+
Bright green
Unknown- K
Light purple pink
Questions:
1.
What inaccuracies may be involved in using flame tests for
identification?
Inaccuracies may be involved in using flame tests for identification
because chemicals could be not cleaned off properly, and end up
messing up the identification of another chemical, they could be
misinterpreted as different colors by different people, and they are
short, so you have to look closely in order to identify colors properly.
Also, there are many that emit similar colors of light, so they could be
mixed up during identification.
2.
Which pairs of ions produce similar colors in the flame tests?
K and the unknown, Ba and Cu, and Li and Sr produced similar colors
in the flame tests.
3.
Explain how the colors observed in the flame tests are produced.
When an atom or ion is heated, it moves from a ground state to an
excited state. As the atom or ion is now in an unstable electron
configuration, the electrons fall back into their normal positions of
lower energy known as the ground state. As they fall back to their
normal positions, the energy absorbed is emitted in the form of visible
light.
4.
5.
Define these terms:
a)
Quanta- the fundamental unit of electromagnetic energy
b)
Ground state- the normal electron configuration of atoms or ions
of an element; the most stable energy state where all electrons in
the lowest energy levels are available
c)
Excited state- when atoms or ions in the ground state are heated
to high temperatures and some electrons absorb enough energy
to allow them to jump up to higher energy levels; unstable
What is a spectroscope? What is observed if the flame tests are
viewed through a spectroscope?
A spectroscope is an optical device for producing and observing a
spectrum of light or radiation from any source. If the flame tests are
viewed through a spectroscope, then you can see several bright
colored lines on a black background. By comparing the positions of
said lines to the known emission spectra of compounds, we can
identify the element.
Conclusion:
This lab allowed us to observe the characteristic colors produced by certain
metallic ions when vaporized in a flame. We used a Bunsen burner to heat the metallic
ions, and the color of the light observed would be recorded. An atom or ion would be
heated to move it from the ground state to the excited state. When said atom or ion
moves from the excited state back to the ground state, the energy absorbed initially, is
released in the form of light. This color can be used to characterize different elements
and help identify unknowns. The unknown chemical in this lab turned out to be a light
purple pink. Another element that turned out about the same color was K +, or
potassium. Using these tests, we can find out what color of light is produced by different
metallic ions and can use the results to identify unknowns.
--