Answer Key
with target levels
Sugar and Water
Particulate Explanations of Physical Change, Strand A Molecular Models of Physical Change
Level 3: Phase change and heating: Can explain that when a solid or liquid is heated, it occupies more volume because of the faster movements of molecules.
Level 2: Mixing of gases: Knows that, when two different gases are mixed, the molecules of the mix together at random. Compression of gases: Knows that when a volume of gas is compressed (or expanded), the molecules move closer together (or further apart) and are still distributed at random, but the molecules do not change their size or their mass. Phase change and heating: Knows that in phase changes, the molecules speed up - from solid to liquid and from liquid to gas.
Level 1: Compression of gases: Knows that when a gas is compressed (or expanded), the number of molecules in that gas does not change.
Level 0: Notions - naive conceptions.
Target level: EPC strand A, level 2
A. Two students pour sugar grains into a glass of hot water. Once the sugar is poured into the water, it is stirred. After stirring, the sugar can no longer be seen.
Why can we no longer see the sugar?
We can’t see the sugar any more because…
Target level: EPC strand A, level 1
B. A picture of the sugar and water particles before they are mixed together is given below.
Which of the pictures below best represents the water and sugar particles after they have been thoroughly mixed together?
A
B
C
D
Target level: EPC strand A, level 2
C. Why do you think the picture you chose is best?
Target level: Argumentation 0d
D1. Two students discuss what they think happened to the sugar.
Laura says: I think the sugar is gone.
Mary says: I think the sugar is still there.
Laura and Mary made two additional observations of the sugar and water.
Evidence #1. After stirring, each student tastes the water. They both agree that the water tastes sweet.
Who does this piece of evidence support? (sugar_d1)
A. Laura
B. Mary
C. Both
D. Neither
Target level: Argumentation 0d
D2. The weight of the sugar, water, and glass before it was added to the water is the same as the weight of the weight of the mixture and glass after the sugar was stirred in.
Whom does the evidence support?
A. Laura
B. Mary
C. Both
D. Neither
Target level: Argumentation 0d
D3. Laura and Mary’s teacher also tells them some information.
Matter cannot be created or destroyed. Whom does this evidence support?
A. Laura
B. Mary
C. Both
D. Neither
Target level: Argumentation 0d
D4. Sometimes a substance breaks into very small pieces when mixed with another substance. Whom does this evidence support?
A. Laura
B. Mary
C. Both
D. Neither
Target level: Argumentation 1c
E. You said that evidence 1 supports: Mary
Complete the last sentence below to explain how the evidence supports Mary’s idea.
Mary says: I think the sugar is still there.
Evidence 1: After stirring, each student tastes the water. They both agree that the water tastes sweet.
This evidence supports Mary’s idea because…
Target level: Argumentation 0c
F. At the end of the class, Mary makes the following argument:
Mary’s argument: The sugar is still there. The total mass stays the same. If the sugar disappeared, the mass would have changed.
What is the evidence in Mary’s argument?
The evidence in Mary’s argument is…
Not scored
G1. Earlier, we showed you a picture of the sugar and water particles before they are mixed together.
Which piece of evidence best supports your answer?
A. After stirring, each student tastes the water. They both agree that the water tastes sweet.
B. The weight of the water glass and the sugar before it was added to the water is the same as the weight of the water glass after the sugar was stirred in.
C. Matter cannot be created or destroyed.
D. Sometimes a substance breaks into very small pieces when mixed with another substance.
Target level: Argumentation 1a
G2. Explain how this evidence supports your answer.
Not scored
H1. You will be asked to explain why one of the other pictures is not as good as the one you chose. Which one do you want to write about?
A
B
C
D
Target level: Argumentation 2a
H2. Evidence
● After stirring, each student tastes the water. They both agree that the water tastes sweet.
● The weight of the water glass and the sugar before it was added to the water is the same as the weight of the water glass after the sugar was stirred in.
● Matter cannot be created or destroyed.
● Sometimes a substance breaks into very small pieces when mixed with another substance.
Why do you think this picture is not as good? Using the evidence above, your own knowledge of mixing sugar and water, or both.