|
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 = 1
What is one problem that this group is investigating? State the problem
in your own words.
|
Component
|
Score
|
Commentary
|
|
Question 1
|
(1)
|
Some understanding of one of the problems investigated
is indicated ("They wanted to see if the pH stayed in the earth
or passed through."). However, the problem is stated incorrectly
in the first sentence; ("This group is investigating the problem
of acid rain and how it affects the soil of the earth.") The
problem is actually how different earth materials affect the
pH of the acid rain solution. |
Question 2 - Event Score = 1
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
|
(1)
|
This response mentions only one variable that
needs to be controlled ("amount of materials") and the explanation
for why it should be controlled is poor. |
Question 3 - Event Score = 1
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
|
(1)
|
This identifies some of the important information
that is provided, however, fails to identify any of the missing
information that is needed to replicate the experiment. |
Question 4 - Event Score = 1
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
|
(1)
|
This response indicates some understanding that
the conclusion should be questioned because different amounts
of solution percolated through the two earth materials. However,
it contains a misconception ("it dissolves into the sand")
and is poorly elaborated. |
|
|
