Devi, what happened to all the ice in the glass?
The ice has melted to become water.
Solid → liquid: meltingWater and its 3 States
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Water is essential to life. We need clean water for our life processes. Although the Earth's surface is mostly covered by water, only a small part of it is clean water, which we can drink and use. How then do we get enough clean water for our life processes?
Water can exist in three states of matter. It can also change from one state to another. The change of water from one state to another during the water cycle helps us obtain clean water.
What I Am Learning
- What are the states of matter that water can exist in?
- How does water change from one state to another?
- What is the water cycle and its importance?
- What is the importance of water to life processes?
- What is the impact of water pollution?
Part 1 · Textbook pp. 31–32
What are the states of matter that water can exist in?
Matter can exist in different states, such as solid, liquid and gas. One example of matter that is readily available to us in all three states is water. We can find water in the solid, liquid and gaseous states around us.
🧩 Let's Connect
In the topic of Matter, you have learnt about three states of matter and their properties.
Water in the solid state is known as ice.
- Ice can be made in the freezer at home.
- In some countries, snow may fall during winter. Snow is made of tiny pieces of ice.
- Large pieces of ice can be found floating in the water in very cold places, such as Antarctica. These large pieces of ice are called icebergs.
Water in the liquid state is often referred to as water.
- Water flows from taps in our homes.
- Rain is water in the liquid state.
- Water can be found naturally in seas, lakes and rivers.
Water in the gaseous state is called water vapour. Water vapour can be found everywhere around us. There is water vapour in the air. Since water vapour is a colourless gas, we cannot see it.
Water vapour that is formed when water boils is also called steam. Steam is also water in the gaseous state.
Key idea
Water can exist in different states, such as solid, liquid and gas.
Answer the quick check to finish this part.
Part 2 · Textbook pp. 33–34
How does water change from one state to another?
Water is matter. It can change from one state to another when it gains or loses heat.
🧩 Let's Connect
In the topic of Heat, you have learnt that matter can change from one state to another when it gains or loses heat.
Let us look at some examples in our daily life where water changes in state.
If we want ice, we can pour some water into the ice tray. Then we place the ice tray in the freezer. The water will become ice again!
Liquid → solid: freezingMother, why is the water in the pot bubbling so much?
MotherThat's because the water is changing into steam. Let me cover the pot.
Liquid → gas: boilingMother, when you lift up the cover, there are water droplets under the cover. How did that happen?
MotherThe steam has changed back into water after touching the cover of the pot.
Gas → liquid: condensationThe four examples on the previous page show that water can change from one state to another.
💭 I wonder…
Water changes in state through different processes. I wonder if there is another process where water changes from liquid to gas without boiling.
Keep this question in mind. You will find the answer in Part 7.
Answer the quick check to finish this part.
Part 3 · Textbook pp. 35–37
Melting
When ice is taken out of a freezer and left on a table, ice will change into water. When ice changes from the solid state to the liquid state, we say that melting has taken place.
ChenI read that ice melts only when it reaches a specific temperature.
AliThat's interesting! Let's find out the temperature at which ice melts.
AliThe graph shows the data collected by the data logger as the ice melts.
ChenLet's analyse the graph to identify the temperature at which ice melts.
Observation · Let's Think and Do: Analysing and interpreting data
Ice is melting, but the temperature stays the same at 0°C.
Explanation
At the start of the investigation, the temperature of ice is 0°C. Ice melts to become water at 0°C. Hence, we observe water dripping down the funnel.
The temperature of ice remains constant at 0°C until all the ice has melted.
The investigation shows that ice melts at 0°C. The temperature at which ice melts is called the melting point of ice.
🔍 Let's Explore
We often add ice cubes into a hot drink to cool it down. Can you explain why the ice cubes are no longer seen after a while?
The temperature of the ice cubes is lower than the temperature of the hot drink. Heat flows from the hot drink to the ice cubes, so the ice cubes gain heat. The heat gained causes the ice to melt at 0°C and become water, which mixes with the drink. That is why we can no longer see the ice cubes. (The drink loses heat to the ice, which is why it cools down.)
Have you ever wondered why ice melts when it is taken out of a freezer and placed on a table? Let's explain this.
Observation:
Ice melts when it is taken out of a freezer and placed on a table.What you have learnt:
Heat flows from a place of higher temperature to a place of lower temperature.Explanation for the melting of ice:
The temperature of ice is lower than the temperature of the surroundings. Therefore, ice will gain heat from its surroundings. The heat gained by ice causes it to melt at 0°C.🌍 Science Around Us
Animals such as polar bears need ice caps to survive. However, due to increasing human activities such as the increased use of transportation and electronic devices, more fossil fuels are burnt to produce more energy. With more fossil fuels burnt, more greenhouse gases are produced. Greenhouse gases trap heat and cause a rise in the Earth's temperature. This causes the ice in the Arctic and Antarctica to melt faster. With fewer ice caps due to melting, the polar bears' survival is threatened.
We can do our part to slow down the rise in the Earth's temperature. For example, we can take public transport and turn off electronic devices when we are not using them.
Answer the quick check to finish this part.
Part 4 · Textbook pp. 38–40
Freezing
Did you know that it is possible to reverse the process of melting? When we put water into a freezer, water becomes ice. When water changes from the liquid state to the solid state, we say that freezing has taken place.
DeviHi, Ali! What are you doing?
AliChen and I found out that ice melts at 0°C. I want to freeze the water now.
DeviUsing this set-up, we can find out the temperature at which water freezes.
AliYes! I have added salt into the ice so that the water in the test tube can freeze faster.
Let's analyse the graph to identify the temperature at which water freezes.
Before freezing
Water remains in its liquid state when its temperature is decreasing.During freezing
Ice starts to form at 0°C. The temperature remains constant throughout freezing.Explanation
At the start of the investigation, the temperature of water is 30°C. The temperature of water decreases until it reaches 0°C.
At 0°C, ice starts to form. The temperature remains constant at 0°C for a period of time. During this time, there is a mix of water in its liquid and solid states. This means that water is changing from the liquid state to the solid state.
The investigation shows that water freezes at 0°C. The temperature at which water freezes is called the freezing point of water. When water is freezing, its temperature remains constant at 0°C.
Have you wondered why water freezes only when it is placed in a very cold environment such as a freezer? Let's explain this.
Observation:
Water freezes when it is left in the freezer for some time.What you have learnt:
Heat flows from a place of higher temperature to a place of lower temperature.Explanation for the freezing of water:
When water is put into the freezer, the temperature of water is higher than the temperature of the freezer. Therefore, water will lose heat to the surroundings in the freezer. The heat lost by water causes it to freeze at 0°C.AliHi, Chen! Guess what Devi and I found out about the freezing point of water. It is the same as the melting point of ice!
DeviYes, both are 0°C!
ChenThat's amazing!
Answer the quick check to finish this part.
Part 5 · Textbook pp. 41–43
Boiling
If you heat water, you will observe bubbles forming in the water after some time. When this happens, we say that water is boiling. When water is boiling, it changes from the liquid state to the gaseous state.
DeviWe have learnt about the temperature at which water freezes and ice melts. Mrs Lim, does water boil at a specific temperature too?
Mrs LimLet's conduct an investigation to find out!
Mrs LimLet's analyse the graph to identify the temperature at which water boils.
Before boiling
Temperature of water increases.During boiling
Water starts to boil at 100°C. Temperature remains constant at 100°C, as bubbles are produced vigorously in the water.Explanation
At the start of the investigation, the temperature of water is 30°C. The temperature of water increases until it reaches 100°C.
When the temperature of water is at 100°C, the temperature remains constant for a period of time. During this time, bubbles are produced vigorously throughout the water. The bubbles contain water in the gaseous state, which is called water vapour. Water vapour that is formed when water boils is also called steam.
The investigation shows that water boils at 100°C. The temperature at which water boils is called the boiling point of water. As water is boiling, its temperature remains constant at 100°C.
Have you wondered why water boils when heated? Let's explain this.
Observation:
Water boils after some time when it is heated over a heat source such as fire.What you have learnt:
Heat flows from a place of higher temperature to a place of lower temperature.Explanation for the boiling of water:
The temperature of water is lower than the temperature of fire. Therefore, water gains heat from the fire. The heat gained by the water causes it to boil at 100°C.Answer the quick check to finish this part.
Part 6 · Textbook pp. 44–45
Condensation
If you place a cool pot cover over a pot of boiling water, you will notice water droplets forming on the underside of the pot cover. Where do the water droplets come from?
Have you ever wondered why water droplets appear on the cold surface of a can of drink that is taken out of the refrigerator? This is because condensation can also happen when water vapour in the air is in contact with a cold surface.
When water vapour in the air comes in contact with the cold surface of the can, the water vapour loses heat to the cold surface. When water vapour loses heat, it changes into water droplets. Water vapour changes from the gaseous state to the liquid state.
🔍 Let's Explore
You will notice mist near the mouth of a kettle when water boils. Think about the heat loss when steam comes in contact with the air outside the kettle. What do you think the mist is made of?
The mist is made of tiny water droplets (water in the liquid state). The steam coming out of the kettle is hotter than the air outside, so it loses heat to the cooler air and condenses into tiny water droplets that we can see as mist. Right at the mouth of the spout there is a small clear gap: that is steam, which is colourless and cannot be seen.
Answer the quick check to finish this part.
Part 7 · Textbook pp. 46–47
Evaporation
Have you observed how wet clothes left out under the Sun become dry after a couple of hours? Or how puddles of water left behind after a heavy rain are not seen after a few hours? These happen because water changes into water vapour during evaporation.
Evaporation involves a change in state from liquid to gas, similar to boiling. However, evaporation can take place at any temperature, unlike boiling. Boiling of water takes place only at 100°C.
What factors affect how quickly evaporation takes place?
Wind, temperature and exposed surface area can affect how quickly evaporation takes place.
💨 Wind
Wind affects how quickly water evaporates. The stronger the wind, the more quickly water evaporates. That is why wet clothes dry more quickly on a windy day.☀️ Temperature
Temperature affects how quickly water evaporates. Water evaporates more quickly if the temperature of the surroundings is higher. That is why wet clothes dry more quickly when hung out on a hotter day.👕 Exposed surface area
Exposed surface area affects how quickly water evaporates. The larger the exposed surface area, the more quickly water evaporates. That is why wet clothes that are spread out dry more quickly than wet clothes that are stacked together.Let's Inquire
- SLS: Water and Its Changes of State
- AB: Activity 2.4
- SLS: Factors Affecting the Rate of Evaporation
Key idea
Water can change from one state to another when it gains or loses heat.
Answer the quick check to finish this part.
Part 8 · Textbook pp. 48–50
What is the water cycle and its importance?
Mother, where does rain come from?
MotherFrom the rivers, lakes and seas.
How does the water in the rivers, lakes and seas become rain?
Condensation and evaporation are two important processes that happen naturally on the Earth so that rain can occur.
This continuous cycle of evaporation and condensation takes place naturally on the Earth at all times. This cycle is known as the water cycle.
🔍 Let's Explore
Imagine that you ran out of clean water while camping. There is a river nearby but the water is not very clean.
How would you make use of evaporation and condensation to get some clean water for use?
The water cycle is very important to our daily life. It helps to provide all living things with a continuous supply of water for survival.
Humans need clean water to survive. While water covers most of the Earth's surface, very little of it is clean water.
During the water cycle, water in water bodies evaporates to form water vapour, leaving behind impurities such as dirt. The water vapour condenses to form tiny water droplets, which gather to form clouds. When rain falls from the clouds, rainwater is collected in reservoirs and has to be treated before it is safe for drinking.
🌍 Science Around Us
Even though Singapore is surrounded by seas, we cannot use the seawater directly for our daily needs. Instead, we need to remove the salt and impurities in the seawater before we can use the water for activities such as drinking, cooking and watering plants. Singapore has desalination plants to produce clean water from seawater. These desalination plants ensure that we have clean water for our daily needs.
Key idea
The continuous processes of evaporation and condensation during the water cycle ensure that there is a continuous supply of water.
Answer the quick check to finish this part.
Part 9 · Textbook pp. 50–51
What is the importance of water to life processes?
All living things need water for their life processes. Let's find out how water is used for our life processes.
Plants also need water for their life processes.
🧩 Let's Connect
In the topic of Plant Transport System, you will learn how different tubes in a plant transport water and food.
As water is important for life processes, we should do our part to conserve water at home and in school!
Key idea
Water is important for life processes. We need to conserve water.
Answer the quick check to finish this part.
Part 10 · Textbook pp. 51–54
What is the impact of water pollution?
Human activity is the most common reason for water pollution. Water pollution causes water in the environment to become unsafe for use.
Rubbish thrown by humans into water bodies causes water pollution.
Oil from ships and boats can spill into the sea, causing the water to be polluted.
Water pollution can damage our environment and harm living things.
Water pollution can cause excessive growth and spread of algae in lakes. These algae then compete with the other living things in the water for oxygen. When the other living things do not have sufficient oxygen, they will die.
Water pollution harms sea creatures. Chemicals and trash thrown into the water may poison and kill the sea creatures.
When we eat fish from polluted water bodies and when we use the polluted water for activities such as farming, harmful substances can be introduced into our bodies.
💡 I'm Inspired
People in many parts of the world do not have access to clean water. Scientists are working hard to find innovative and affordable ways to help the people living in these places to obtain clean water.
Some examples of such inventions are the Fog Catcher and the 'Drinkable Book'. Efforts are still going on to test how well these innovations can solve the problem of lack of clean water in some parts of the world.
Key idea
Water pollution has a negative impact on living things and the environment.
Answer the quick check to finish this part.
Part 11 · Textbook pp. 55–57
Let's Apply
These are the five questions from the end of the chapter. Choose an answer to see whether you are right and why.
Your score
0 / 5
Answer all five questions.
Part 12 · Textbook pp. 58–59
What I Have Learnt
- Water can exist in different states, such as solid, liquid and gas.
- Water can change from one state to another when it gains or loses heat.
- The continuous processes of evaporation and condensation during the water cycle ensure that there is a continuous supply of water.
- Water is important for life processes. We need to conserve water.
- Water pollution has a negative impact on living things and the environment.
Keep going!
Finish every part to complete the topic.