This item assesses the students' abilities to:

• successfully perform a simple paper chromatography experiment
• interpret the results, and
• infer how the technique might be used by professional scientists

A good response will correctly identify the dyes used in yellow, green, and brown M&M candies and will explain, using an example, how and why the results of this type of analysis are useful.

An excellent response will show precision in the recording of experimental data and will display an understanding of the process and/or its applications beyond what is required for this experiment.

Rubric

Criterion 1:		The response makes a statement about the movement or color of dyes on at least one of the chromatography strips, even if the statement is likely incorrect (e.g., "The brown dye produced black and yellow bands.") (Question 1) OR The response suggests one way such an analysis could be used, even if chromatography could not actually be used for that purpose. The suggestion must, however, indicate that the student understands that chromatography is used to determine the composition of something, or to separate components. (Question 2) Acceptable: "You could use it to see how much sugar is in the candy." Unacceptable:"You could use the strips to find out if the yellow dye will stain clothing."
Criterion 2:		The response correctly identifies the dyes used in at least two of the candies (yellow = yellow; green = blue and yellow; brown = red (rust, orange) blue and yellow). The response may identify an additional color intermediate between two correct colors (e.g. green = blue, green, and yellow) as long as it includes the correct colors. (Question 1) AND The response suggests at least one way that the results of such an analysis could conceivably be used (e.g. "to make accurate food labels",) "to see if it might contain something someone is allergic to.") The response "to see if it contains poison" is acceptable for this criterion, as are responses that rephrase portions of the question such as "to see if a chemical reaction has occurred" or "to separate a mixture." (Question 2)
Criterion 3:		The response includes a careful and detailed record of experimental observations and results, including either the relative distances that the different colored dyes travelled for all three M & M colors or the relative speeds at which they travelled, AND the response correctly identifies the dyes used in all three candies. (Question 1).
Criterion 4:		The response displays a level of scientific understanding beyond that demanded by the prompt. This understanding may be evidenced in several ways: (Question 2) The response may explain how chromatography is used to determine whether a chemical reaction has occurred. Chemical reactions from new substances with different physical properties than the starting materials. One of these physical properties is the speed and distance of the substance's travel along the chromatography paper. The response relates the speed and distance of the substance's travel to its affinity for the paper phase; the component with the lowest affinity for the paper will travel fastest and farthest. The response names and briefly describes at least one other method of chromatography, such as gas chromatography. The response cites at least one real use of any method of chromatography within the scientific community. For example, chromatography is used to selectively cleave and purify peptides.