administration student task rubric student work technical quality
Identifying Elements
Contributed by: Council of Chief State School Officers (CCSSO)

Item Description:
The content of this event concerns the emission spectrum of elements. When an element in gaseous form is excited by something such as electrical current or heat, it gives off light which can be separated into colors using diffraction glasses. Each element has a distinct spectral pattern and these patterns can be used to identify elements.

For this event, the students are asked, using diffraction glasses, to find the similarities and differences between the observed spectrum of a fluorescent light and an incandescent light. Incandescent lights use an excited solid. Excited solids emit white light which separates into all the colors of the spectrum. Fluorescent lights use a tube of excited gas as a light source. Unfortunately, this gas may vary considerably between different bulbs and may contain one color or many when the light is separated. For this reason, the colors of the spectrum may be a difference or a similarity of the different types of bulbs.

The students are then given several solutions containing various elements. The students dip a nonreactive wire loop into the solutions and place the wire into a flame while observing the color of flame. The solution vaporizes into an excited gas which will give off the spectral colors for that element. The students record the colors they saw in the flame with a colored pen. One of the solutions is a repeat without a label. The student is asked to identify the solution by comparing it's flame color to the other solution flame colors.

The third question asks the student how they would go about finding out the identity of the solutions if the labels were missing. Assume this is after they performed the event with the labeled solution.

Major Content Points:
1. Light can be separated into constituent colors. The student should understand that normal light is actually a combination of many colors. The exact identity and order of these colors isn't as important.

2. When excited, different elements give off different colors of light. The student should realize that emission spectrum of all substances are not the same.

3. An emission spectrum is a trademark of an element. The student should understand that two elemental substances with the same emission spectrum are the same element.

ME130 Rubric

Criterion 1:
In question 1, the student must use colors to compare the two bulbs. Shape or brightness of the colors doesn't fulfill the criterion. Color can be noted as a similarity or a difference.

  1. Both lights had the same basic colors.
  2. One had more colors than the other.

Criterion 2:
In question 2, the student must state that the solutions gave off different colors when heated. This can be done by either mentioning that the solutions gave off different colors or by comparing each solution individually.

  1. The unknown was different from all the other solutions except for sodium.
  2. The unknown was blue and green, the barium was yellow the sodium was . .

Criterion 3:
In question 2, the student must attempt to identify the unknown and use similar colors as a reasoning. The identity can be any of the solution or a mix, but they must mention color matching as a reason.

  1. The unknown is probably sodium because they are both orange.
  2. The unknown is blue and green, potassium is blue and copper is green, so the unknown is a mix of potassium and copper.

Criterion 4:
In question 3, the student must mention finding the flame color of the unlabeled solutions or that they tested the unlabeled solutions. Simply saying they would use the colors of the solutions doesn't demonstrate a grasp of the technique.

  1. I would test to find the colors of the unlabeled solutions.
  2. I could use the flame colors.


©1997-2005 SRI International. All rights reserved. Terms of Use