Matter and its Three States
Properties of Gas
This science revision note aims to help your child
– identify the correct setup based on the properties of the air
– proper scientific keywords to explain the concepts clearly.
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Paul had two identical syringes. One was completely filled with air and one was completely filled with sand. He pushed his thumb securely against each nozzle and tried to push the plunger down. An example of his setup is as shown.
He then plotted a graph of the distance travelled by the plunger with the force exerted on the plunger.
Which graph (graph A or graph B) represents which syringe (syringe containing air or syringe containing sand)? Explain your answer.
STEP 1
Decipher the two graphs.
- In graph A, the distance travelled by the plunger increases more. This means that the plunger was able to be pushed down the syringe more.
- In graph B, the distance travelled by the plunger increases much less. This means that the plunger was able to be pushed down the syringe only very slightly.
STEP 2
What does pushing the plunger down the syringe mean?
When the plunger is pushed down the syringe, the space inside the syringe decreases. This means that the volume of the substance inside the syringe decreases as the substance is able to be compressed.
STEP 3
Which substance, air or sand, is able to be compressed? To identify this, consider whether each substance has a definite volume or not.
- Air is a gas and does not have a definite volume. This means that it can be compressed.
- Sand particles are solid and have a definite volume. This means that they cannot be compressed. However, sand has a lot of tiny air pockets in between the sand particles. The air pockets are gas and do not have a definite volume, meaning they can be compressed. Hence, the sand can be compressed slightly.
FINALLY, put your answer together
Question: Which graph (graph A or graph B) represents which syringe (syringe containing air or syringe containing sand)? Explain your answer.
Answer:
Graph A represents the syringe with air while graph B represents the syringe with sand.
The distance travelled by the plunger increases much more in graph A than in graph B.
Sand particles are solid and cannot be compressed. However, the air pockets between the sand particles are gas and do not have a definite volume, meaning they can be compressed. Hence, the sand in syringe B can only be compressed slightly compared to the syringe in graph A which contains air only.
Common mistakes
Wrong explanation: Graph A represents the syringe with air because air does not have a definite mass, while graph B represents the syringe with sand because sand has a definite mass.
Mass is not relevant to this question. The volume of a substance refers to how much space the substance takes, while the mass of a substance refers to the amount of matter in the substance. When the plunger is pushed down the syringe, this affects the amount of space the substance takes, and does not affect the amount of matter in the substance. Hence, whether the plunger is able to be pushed down or not depends on the volume and not the mass of the substances.
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Andy Ling
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