In our previous articles on the topic of Matter, we have discussed that all matter has mass and occupies space. Students tend to understand the concept of the properties of matter but encounter difficulty in applying the concept when answering questions.

In this article, we will be going through the thought process on how to tackle a different type of application questions testing on the properties of matter. Additionally, we will also analyse a bonus question that has confused many students.

## Background Information

Firstly, let’s recall what are the properties of the three different states of matter: solid, liquid and gas.

When an object is said to have no definite shape, it means that the object takes the shape of the container that it is placed in and is either a gas or a liquid. On the other hand, an object that is in the solid state has definite shape and does not take the shape of the container that it is placed in.

So, what does it mean by “gases can be compressed”?

To put it simply, what this statement actually means is that gases can be squeezed. Many of you know that compression of gases is caused by applying a force onto the gas.

Did you know that we can also cause gases to be compressed by adding more gas into the same container?

To understand the concept of compression of gases better, here are some diagrams to help you visualise:

### Here’s What A Solid Looks Like:

Let’s take one black ball as one unit of solid particle. As seen in the diagram above, solid particles are closely packed to each other.

There is no “space” for the solid particles to move. In this case, even when a force is applied to the solid particles (as seen above), the solid cannot be compressed.

### Here’s What A Liquid Look Like:

As seen from the diagram, although the liquid particles (blue balls) are not as closely packed compared to the solid particles, there is still not much “space” for the liquid particles to move.

Hence, similarly, the liquid particles would not be able to compress even when a force is applied to them.

### Now, Here’s What A Gas Looks Like:

As seen from the diagram, there is plenty of “empty space between the 4 units of gas particles (orange balls). With this “empty space” between the 4 units of gas particles, the gas particles have space to move. Thus, this allows the gas particles to be compressed.­

As mentioned earlier, compression can occur in two scenarios for gases.

## Scenario #1: Applying a Force on the Gas

This scenario occurs when the container of the gas becomes smaller, as seen in the diagram below. This pushes the gas particles closer to each other, reducing the “empty space” between the gas particles, which is also known as COMPRESSION.

## Scenario #2: Adding More Gas into the Same Container

This scenario occurs when the container remains the same size, however, more units of gas particles are placed into the container. This reduces the “empty space” between each unit of gas particles, creating the effect of COMPRESSION, as shown in the diagram below.

Now that we’ve revisited the properties of the different states of matter and delved deeper into the concept of compression, let’s take a look at the following question!

## Let’s Try A Question

Source: St. Nicholas Girls’ School – 2017 P5 SA2 Science Examination Paper [Q35]

Part (A): Air can still be pumped into the inflatable mattress even when it is fully inflated. State a property of air that allows this to take place.

### Thought Process

Firstly, we need to identify that the state of matter of air is gas.

One property of gas is that it has no definite volume and can be compressed. Hence, even when the mattress is fully inflated, air can still be pumped into the mattress as there are “empty spaces” between the air particles, just like in the aforementioned Scenario #2.

Air does not have a definite volume and can be compressed.

Part (B): Will the mass of the inflatable mattress increase, decrease or remain the same after more air is pumped into it? Give a reason for your answer.

### Thought Process

Air is matter, which has mass and occupies space. By pumping more air into the inflatable mattress, it means that more matter is being introduced into the inflatable mattress. With more matter, there will be more mass, thus the mass will increase.

The mass of the inflatable mattress will increase. When more air is pumped into the mattress, there will be more matter in it, causing the mass of the inflatable mattress to increase.

Part (C): When the inflatable mattress is left in the hot sun for a few hours, it became firmer. Explain why.

### Thought Process

The presence of the hot sun indicates the presence of heat. The air in the mattress will gain heat from the hot sun and expand. As the fully inflated mattress has a definite volume, the volume of the mattress did not change. This causes the expanded air to exert a greater push force against the inner walls of the mattress, causing the mattress to become firmer.

The air in the mattress gained heat from the sun and expanded and increased in volume. The expanded air will exert a greater push force against the inner walls of the mattress, causing the mattress to become firmer.

## How Would Volume & Mass Change Under Different Conditions?

Let’s now take a look at the following conditions and determine under what situations would the volume and/or mass of gases change or remain the same!

### Condition #1

• Mass of the gas remains the same
• Volume of the gas decreases

This can occur when you decrease the size of the container but do not add or remove any matter from the container.

One common example is the action of pushing the syringe filled with air.

As seen from the diagram above, the syringe was filled with air with its tip sealed so that no air can escape. When a force is applied by pushing the plunger in, the air becomes compressed. Hence, the space taken up by the air is now smaller (as seen below).

This shows that there is a decrease in the volume of the gas (although the mass of the gas remains the same). This is an example of COMPRESSION, by applying force on the gas.

### Condition #2

• Mass of the gas increases
• Volume of the gas remains the same

When the mass increases, it means that more matter has been put into the container. However, as the container (solid – has a definite volume) did not change its size, the volume of the gas would remain the same.

This is also another example of COMPRESSION by adding more gas into the same container. This is similar to Part (B) of the question we’ve just analysed.

### Condition #3

• Mass of the gas remains the same
• Volume of the gas increases

As the mass of the gas remains the same, we’re able to conclude that there is no addition or removal of gas from the container. How can the volume increase with no increase in mass?

A classic example of this will be one of the Heat Energy questions in the from our CCI™ (Complete Concept Integration) course.

“How do we remove the cork from the bottle without touching the bottle?”

As seen from the above diagram, the cork can be removed from the bottle by applying heat to the bottle! When the air in the bottle gains heat from the heat source, it expands and increases in volume.

The expansion of air in the bottle would exert a push force on the cork, pushing it out of the bottle (as indicated by the arrow). This is an example of EXPANSION.

### Condition #4

• Mass of the gas increases
• Volume of the gas increases

A common example of this can be seen when you hold parties at home!

When you try to inflate a balloon, you blow air into the balloon (as indicated by the arrow in the diagram below). This causes more air to enter the balloon, increasing the amount of matter in the balloon. Thus, the mass of the gas in the balloon increases.

As the balloon is made out of an elastic material, the balloon gets larger as more air is blown into the balloon. As the size of the balloon increases, the volume of gas in the balloon also increases. This is another example of EXPANSION.

After reading this article, I hope you are now more confident in answering questions that involve applying the concept of the properties of matter.

Before you go, why not try the following question?

## Let’s Try A Bonus Question!

If I take 100 cm³ of air out from a container with a capacity of 500 cm³, what is the volume of air left in the container?

Students tend to think that the answer is 500 – 100 = 400 cm³ of air left in the container. But this is INCORRECT!

The correct answer is 500 cm³! This is because air has no definite volume. Air would expand to occupy the extra space in the container, causing the volume of air in the container to remain the SAME at 500 cm³.

Note: The MASS of the gas decreases as air is taken out since matter is being removed from the container.

Stay tuned for more articles! 😀

If you like our methodology, please click here to explore our Matter Techniques™ Masterclass for P5 & P6 students.