Author(s): Denise Agapoff & Harold Collier
Discrepant Event - Teacher's Guide
SED 695B; Fall 2005
Detailed Explanation of Discrepant Event

Principles illustrated

  • bleaching agents
  • oxidation/reduction
  • chemical change
  • chemical reaction

By burning the sulfur, sulfur dioxide gas (SO2) is formed.
The red coloring in the rose is being reduced and turns white. Therefore, the sulfur dioxide is acting as a bleaching agent as well.

SO2 + red rose pigment---> SO42- + reduced pigment (white)

Going further: the reduced pigment (white) can be oxidized again by putting the rose in nitrogen dioxide gas. See video below.

reduce pigment (white) + NO2---> NO + oxidized pigment (red)




Questioning Script

Prior knowledge & experience:

Root question:

  • What is happening to the color of the rose?

Target response:

  • Burning sulfur must be bleaching out the color

Common Misconceptions:

  • While the rose wilted from the heat produced from the burning sulfur, it did not die yet its color was removed.

Other possible questions:

  • What part of the rose started to change color first?
  • What type of reaction is taking place?
  • What gas is formed when sulfur burns?
  • What other bleaching agents do you know?
  • What is the function of the watch glass over the beaker?



Attach the wire to the stem of the rose

Let it hang from the side of a beaker

Place a small amount of sulfur powder in a crucible

Drop a match into the sulfur

Immediately cover the beaker with a watch glass and place in a fume hood

For best results - keep covered

Safety precautions

The sulfur dioxide produced is a very pungent gas and is also poisonous when inhaled in large doses

This experiment should only be done in a fume hood or outside

References & Links:

Science Inquiry
Discrepant Events
A collection of demonstrations from the 1999 NSTA conference
Video Source