In Primary 4, we learn about the 3 states of matter (in actuality there’s more, but that’s outside of the PSLE syllabus). This is a crucial foundational topic, as it is linked to other topics like heat, and later on the water cycle in primary 5. So, let’s explore the key points in Properties of Matter!
Firstly, the definition. What is matter?
Matter is anything that has mass and volume!
Volume is the amount of space that an object occupies. Think about size!
Who has more volume? Obviously it’s Ms Elephant- she occupies way more space than Mr Ant! If we place both of them in a bathtub, Ms Elephant will displace more water (occupy the space previously occupied by water) and cause a bigger splash. Whereas Mr Ant will barely displace any water. No water flows out of Mr Ant’s tub.
Now, think about what apparatus we can use to measure volume. Clue: think about water when it comes to volume.
We use measuring cylinders and beakers! The unit(s) for volume is:
Liquids → Mililitres (ml), litres (l)
Solids → Cubic centimetres (cm³)
On to mass!
Mass is the amount of matter/ substance in an object. Think about how heavy the object is.
Ten tonnes has more mass than a feather.
To measure mass, we use weighing scales and balance scales. The unit(s) for mass is: Grams (g), kilograms (kg), tonnes (t).
Even in ancient days, the Egyptians believed that a balance scale would be used to weigh your heart against the feather of truth! They believed that the heart recorded all of the good and bad deeds of a person’s life and was needed for judgment in the afterlife. If the heart was heavier (had more mass) than the feather, the person would be condemned. Whereas if they were of the same mass, that person could enter paradise.
Solid, Liquid and Gas
There are three states of matter: Solid, Liquid and Gas. To categorise them, the properties students should know are:
- Does it have a fixed/ definite shape?
- Does the shape stay the same with no push force applied?
- Does it have a fixed/ definite volume?
- Does the amount of space occupied stay the same even with force applied?
- Can it be compressed?
- Does the space occupied decrease with force applied?
Properties of Matter: Solid, Liquid and Gas
(please remember this table!)
By “fixed shape”, what do we mean? If you leave the item alone on a table, will its shape change? If no pressure/ force is applied and the shape stays the same, we can conclude that the object has a fixed shape. Only solids have a fixed shape. (The words “fixed” and “definite” are interchangeable)
A common misconception is that sponges are not solids. This is not true! Sponges are solids as they have a definite shape and definite volume. The reason it can be compressed is due to the air spaces in the sponge.
Syringe Compression Experiment: Properties of Matter
Only solids and liquids have a definite volume. The space they occupy is fixed. However, gases do not have a definite volume. How can we tell? We do the syringe compression experiment:
- Take a syringe and pull the plunger to fill the syringe with air.
- Cover the nozzle with your finger
- Push the plunger to see air being compressed!
- Repeat steps 1-2. But this time, pull the plunger to see air expanding.
The air molecules are so far apart that they can be forced together. The distance between its molecules makes gas unique, so it is the only state of matter that can change its volume/ amount of space occupied. So whenever a question states that a substance can be compressed, it must be gas.
You can try the compression experiment with a syringe filled with water, and a syringe filled with salt! Both do not compress, showing that liquids and solids have a fixed volume.
Let’s go through some common exam questions and misconceptions!
Question 1: Gases can be compressed. Explain why.
Wrong answer: Gases have no fixed shape. ✖
Correct answer: Gases have no fixed volume. ✔
Liquids have no fixed shape, yet cannot be compressed. Liquids have a fixed volume. They occupy a fixed amount of space. (Remember, think about size!)
Question 2: taken from Nanyang 2023 SA2
Recall that gases have no definite volume, while liquids have definite volume. The reason why the plunger can move inwards is due to the compression of air.
The answer is (4) ! Did you get it right?
Question 3 (i):
No matter how much air is pumped in or removed, the volume of air in the container will stay the same. Please ignore the addition/ subtraction of air! It is a distractor.
The formula to solving such questions is:
Total container volume – Liquid/ solid volume = The volume of air in the container
So 500- 50 = 450. The answer is (2) !
Question 3 (ii):
Based on part (i), what happens to the mass of air in the container?
Answer: The mass increases. Air has mass, so more air pumped in means more mass.
Question 4: Bob inflates two balloons and balances them on a balance scale.
He pops the balloon on the right. What happens to the scale? Explain your answer.
Do take note that students must describe the direction of movement carefully.
Answer: The balloon on the left moves downwards as it has more mass.
The balloon on the right moves upwards as it has less mass.
Many students tend to just write “the pole tilts at the left balloon” ✖✖✖
“Tilts” is a very ambiguous word. Please be specific!
Question 5: In which container can 100cm³ of air be pumped into?
Answer: all of the above! Air can be compressed as it has no definite volume.
Question 6: taken from Nanyang 2023 SA2
Clue: Students must be able to identify the invisible “ghost” in the bottle, and whether that substance can escape.
Answer: When he lifts the funnel, air in the bottle can escape. (please state “in the bottle”. There is air in the surroundings as well, be specific!)
Soy sauce can flow in to occupy space previously occupied by air.
(remember this key phrase!)
Just like how on buses or the MRT– imagine people squeezing in to enter while you are trying to get out. It’s so difficult for you to exit, and it’s difficult for them to enter!
You occupy space, just like air in the bottle occupies space.
So people trying to enter will enter with great difficulty, just like how the soy sauce drips slowly into the bottle.
The solution? Create another exit door! This is similar to how he lifted the funnel.
I hope this article helped you understand the properties of matter more clearly, and remember the key phrase “occupy space previously occupied by” (also known as displace).
Till next time! 😊
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