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.