Physical Science

Experiment 8-3

Flame Colors

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Background Information

We humans are blessed with marvelous detectors of much diversity in our environment, our eyes.  While there is a well established common sense understanding of color vision, that understanding is flawed.  (See Primary Colors: Not and Color Vision: a Dialogue in the Style of Galileo.)  But it is accurate that most of our knowledge about the world is gained through vision.  It has long been known that various substances can influence the color of flames.  This experiment will start a careful investigation of that phenomena, an investigation which later reveals the secrets of chemistry and physics evidence about the unexpected behavior of the most basic building blocks of the universe.

Experiment

flame apparatus In this experiment small amounts of several compounds, suspended on small loops of wires with insulating wood handles, were held in the flame of a propane burner.  Each wire glows white when hot but has been chosen to not contribute significantly to color of the flame.  The burning air-propane mixture glows bright blue near the burner, but contributes very little to the higher flame.  The flames were photographed with a Canon S30 digital camera for your viewing.

Camera mechanisms are different from the mechanism used by human eyes to detect colors.  The colors seen by eyes and cameras are approximately the same.  However the eye typically adjusts to bright light by tiring over time resulting in a changing perception of color.  Camera film and charge coupled devices used in digital cameras don't tire, but bright light often appears whiter.  For example, the light coming directly from the middle of the flame to the right looked to the eye like a brighter yellow than the edge of the flame, not white.


Procedure

Look at the photographs below and compare the colors.
  1. Are all flames colored by chloride (Cl) compounds the same color?
  2. What part of the chemical compounds seems responsible for contributing most of the color?
BaCl2
BaCl2
CaCl2
CaCl2
CuCl2
CuCl2
KCl
KCl
LiCl
LiCl
NaCl
NaCl

Record your results in your science journal.  Write a Formal Report if you need to earn credit.


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5/31/2003
revised 6/1/2003
by D Trapp
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