PALS - Examples of Student Work

Soiled Again

Examples of Student Work

Contributed by: Connecticut Academic Performance Test (CAPT)

A group of students prepared a vinegar-and-water solution to simulate acid rain. After determining its pH, they poured the solution through cups that contained various earth materials (sand, potting soil and crushed limestone). The students measured the amount of solution that percolated (passed) through a hole in the bottom of each cup in a set amount of time, and they tested the pH of the drippings.

The results of the group's experiment are shown in the following table.

Earth Materials	pH of "acid rain" before percolation	Amount of "acid rain" percolated in 3 minutes	pH of percolated "acid rain"
sand	3.0	30ml	3.5
potting soil	3.0	20ml	3.5
crushed limestone	3.0	90ml	5.0
all three Earth materials	3.0	50ml	5.5

Question 1 - Event Score = 2

What is one problem that this group is investigating? State the problem in your own words.

Component	Score	Commentary
Question 1	(2)	This response correctly identifies the independent variable ("earth material") but the dependent variable is poorly stated ("absorb acid rain.") It is less elaborated than the score 3 responses.

Question 2 - Event Score = 2

What are the variables that need to be controlled in this experiment? Explain why it is important to control them.

Component	Score	Commentary
Question 2	(2)	This response discusses two variables that are important to control ("percent of acid in the acid rain solution" and "amount of acid rain poured"). The discussion of why these variables need to be controlled is incorrect.

Question 3 - Event Score = 2

Do you have enough information to replicate this group's experiment? If you think you do, tell what information you have. If you think you do not, tell what other information you would need.

Component	Score	Commentary
Question 3	(2)	This response discusses the need to keep the amounts of acid rain and earth material constant, but does not mention the need to know the amounts used. It is not as elaborated as the score 3 responses.

Question 4 - Event Score = 2

The group concluded that sand and potting soil have the same ability to neutralize acidity because in each case the pH went from 3.0 to 3.5. Based on this group's experiment and results, do you think the group's conclusion is valid? Explain why or why not.

Component	Score	Commentary
Question 4	(2)	The response correctly questions the validity of the results because the amount of earth materials used is not stated. There is no discussion of the percolation rates of the materials and its relationship to the materials' neutralizing ability.

Question 1 - Event Score = 2

Question 2 - Event Score = 2

Question 3 - Event Score = 2

Question 4 - Event Score = 2

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