Download Modified copy of Flame Tests 2013

Flame Tests
Background
While Rutherford's experimentation and model helped to explain the inner structure of the atom, it did very
little to explain the chemical behavior and periodicity of the elements. The next clue toward understanding the
nature of atoms was to come from a very different study of chemistry-spectroscopy.
Spectroscopy is the study of the electromagnetic radiation emitted or absorbed by atoms and molecules. Several
scientists in the early 1900's used spectroscopy as an important tool for investigating the nature of the different
elements. As you will learn later in this module, spectroscopy also supported Rutherford's model, in part by
providing evidence that the electron does not spiral into the nucleus.
In this experiment, you will observe the light emitted by several different elements. Keep in mind that at one
time, this was the most advance evidence available to scientists who were searching to understand the inner
workings of the atom.
The beautiful colored flames that you observe in this experiment are put to work commercially in the form of
fireworks. Most fireworks incorporate metal ions used in this lab to produce the common fireworks colors: blue
(copper), green (barium), red (strontium), and orange (calcium). Magnesium is also used to produce white
light.
Although the color of a flame is said to be particular to the kind of metal atom, the color of the fireworks flame
is considerably different from that seen in the laboratory. This effect is primarily due to the presence of
oxidizers and fuels that produce unwanted colors or otherwise mask the light given off by the coloring agents.
Sodium is often viewed as an impurity because a small amount of sodium can cause a significant change in
flame color. The metal ions are usually bound to an anion (a negative ion), forming a solid at room temperature.
The anions influence the temperature of the flame. For example, a flame containing barium nitrate will burn at
a higher temperature than barium chloride. This difference in temperature sometimes causes different hues to be
emitted from the same metal ions.
Objectives
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Observe the characteristic emission spectra of several gases and metallic ions.
Identify the metallic component(s) of an unknown solution based on flame color and spectrum.
Materials/Equipment
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Samples of the following metallic salts
o calcium chloride
o copper chloride
o iron chloride
o lithium chloride
o potassium chloride
Bunsen burner and accessories
Safety goggles
Lab apron
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o
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o
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sodium chloride
strontium chloride
unknown 1
unknown 2
Splints soaked overnight in distilled water
250 mL beaker half full of distilled water
Pre-Lab
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What is a photon?
Describe how atoms give off light. Be sure to include the following terms in your description: electron,
photon, energy level, excited state, ground state.
How are colors of light related to the electromagnetic spectrum?
How are colors of light related to energy?
Procedure
1. Place the end of one of the toothpicks soaked in a solution into the flame. Note color(s) of the
flame and the duration of each color. Immerse the wooden splint in the distilled water to fully
extinguish it, and then discard it in the trash. Record your results.
2. Repeat step 4 for each of the remaining salts.
3. Repeat step 4 for each of the unknown metals and predict the identity of the unknown metals.
Repeat any of the known metals to help with this prediction.
** Wash hands thoroughly before leaving the lab.**
Some of the salts used are poisonous or irritating to the skin. Keep your hands away from your mouth until
after you have washed them and have left the laboratory.
Data Table: Metallic Salts
Formula
Metal Ion
Color seen
wavelength
Analysis
1. What was (were) the identity of the metal ion(s) in the unknown solutions? Give evidence.
2. Predict the flame color if metallic ions of copper and strontium were mixed.
3. Based on the flame colors in this experiment, which single element would most likely be used to
produce yellow fireworks? Why?
4. Why do the metals give off light?
5. Which of the flames that you observed gave off the most energy?
6. Why do some of the samples give off more than one color flame?