class 6 Science Chapter 8 notes

Class 6 Science Chapter 8 A Journey Through States of Water – easy notes, concepts, NCERT book solutions, important questions, worksheet and answers. Learn about ice, water and water vapour, changes of state, evaporation, condensation, melting, freezing and the water cycle in simple language.

Zoom:

Class 6 Science – Chapter 8

States of Water

Chapter at a Glance: Water can exist in three states — solid, liquid and gas. Ice is the solid state, water is the liquid state and water vapour is the gaseous state. Water changes its state when it is heated or cooled.

1. States of Water

Water can be found in three different states:

Solid: Ice
Liquid: Water
Gas: Water vapour

Water changes between different states during the water cycle.

Aavi has a counterview to Thirav. What do you think? Why?

Ice and water are the same substance because ice changes into water when heated and water changes into ice when cooled.

Do you think Thirav is right? How can you find out?

We can put water in a freezer and observe that it changes into ice. We can also leave ice at room temperature and observe that it changes into water.

Activity 8.1: Let us observe

Put an ice cube in a cup, leave it on the table and observe.

Observation: Ice gets converted into water.

What can you conclude from the observations?

Ice changes into water. Therefore, ice and water are different states of the same substance.

Does this mean that ice and water are the same substance?

Yes. Ice and water are two forms, or states, of the same substance.

Remember: Ice is hard and does not flow. Water flows and can splash.

2. Investigating Water’s Disappearing Act

Have you ever noticed water in the puddles disappearing? Where does it go? Discuss with your friends.

Yes. Water in puddles slowly changes into water vapour and mixes with the air. This process is called evaporation.

Where else have you seen water disappearing? Can you think of a possible reason why this happens?

Water disappears from wet clothes, mopped floors and our skin. It happens because water evaporates.

Does the reason you thought earlier to explain water disappearance apply in this case also?

Yes. Water left on utensils can evaporate into the air.

Thirav thinks that water does not seep through the surface of the utensils. Design an activity to investigate whose idea is correct.

Take a tablespoon of water on a steel plate. Observe the other side of the plate and keep watching the water. If no water appears on the other side and the water slowly disappears, it shows that water is not passing through the steel plate.

Activity 8.2: Let us investigate

Take a tablespoon of water on a steel plate.
Observe whether water seeps through to the other side.
Keep observing until the water completely disappears.

What do you infer? Is this activity enough to come to the conclusion that water does not seep through a steel plate?

We infer that water does not seep through the steel plate. However, we should make careful observations and repeat the activity to be more certain.

If water does not seep through the steel plate. Then, where has the water gone?

The water has changed into water vapour and mixed with the air.

While making dosa, we sprinkle some water on the hot pan and it disappears. Where does it go?

It changes into water vapour or steam because of the heat.

Can you think of other examples of evaporation?

Drying of wet clothes, drying of a mopped floor and drying of sweat are examples of evaporation.

Now what do you think is the reason for the disappearance of water from the puddles? Is it due to: (i) seeping of water into the ground or (ii) evaporation of water or (iii) both of these?

It can be due to both. Some water may seep into the ground and some water may evaporate.

Hand sanitiser disappears as you rub it on your hands. What happens to it?

The sanitiser evaporates because it contains liquids that evaporate quickly.

Evaporation: The process of conversion of water into its vapour state is called evaporation.

3. Another Mystery – Water Droplets on a Cold Glass

Activity 8.3: Let us experiment

Take cold water in a glass tumbler.
Add a few ice cubes.
Leave it undisturbed for five minutes.
Observe the outer surface of the glass.

Suggest possible reasons explaining the appearance of water droplets on the outer surface of the glass tumbler.

Water vapour present in the air comes in contact with the cold surface of the glass and changes into tiny water droplets.

Where else have you seen water droplets like this?

We see water droplets on cold bottles, cold glasses and plants as dew drops.

Why do we see dew drops more in the morning?

During the night, surfaces become cool. Water vapour in the air condenses on these cool surfaces and forms dew drops.

When we boil the water in a half-filled utensil and cover it with a steel plate, some water drops accumulate on the inner side of the steel plate. Where do these water drops come from? What do you think?

Water changes into water vapour while boiling. When the vapour touches the cooler steel plate, it condenses into water droplets.

Condensation: The process of conversion of water vapour into its liquid state is called condensation.

Evaporation and condensation are opposite changes of state.

Activity 8.4: Let us measure

Take a glass tumbler half-filled with water containing a few ice cubes.
Cover it with a small steel plate.
Weigh it on a digital weighing balance.
Record the mass every five minutes for 30 minutes.

Predict what will happen to the mass of cold water kept on the digital weighing balance. Will it increase or decrease or remain the same?

The mass may increase slightly because water vapour from the air condenses on the cold outer surface of the glass.

Do your findings match with your predictions? Explain your observations.

The findings may match the prediction. Water droplets form outside the glass because water vapour from the air condenses on the cold surface.

Can we conclude that water is not seeping through the wall of the tumbler?

Not conclusively from this activity alone.

Can we also conclude that the water collected outside the tumbler is only due to condensation?

No. We need further evidence.

What more can you do to show that water is not seeping from the glass tumbler?

Mark the water level inside the tumbler and observe whether the level decreases.

How would you modify Activity 8.4 to find the answer?

Mark the water level with a permanent marker or visible tape and check the level after some time.

What do you observe? Water level in the glass tumbler does not go down but the extra water gets collected on the outer surface of the glass tumbler. What can you conclude from this?

Water is not seeping through the glass. The water outside is formed mainly by condensation of water vapour from the air.

Humidity

Humidity is the amount of water vapour present in the air.

4. What are the Different States of Water?

Water exists in three states:

State	Example	Main Property
Solid	Ice	Fixed shape; does not flow
Liquid	Water	Flows and takes the shape of its container
Gaseous	Water vapour	Spreads throughout available space

Activity 8.5: Let us identify

What changes do you notice in the shape of the ice cube?

The ice cube retains its shape when moved to another container.

Did you notice how water flows from one container to the other? What happens to its shape?

Yes. Water flows and takes the shape of the container.

What are the differences in the properties of water in solid, liquid and gaseous states?

Solid water has a fixed shape. Liquid water flows and takes the shape of its container. Water vapour has no fixed shape and spreads through available space.

Does water also possess the property to spread?

Yes. Water spreads on a surface while its total volume remains the same.

Look around and find some examples of solid substances.

Stones, wood, glass, books and ice.

What are the other examples of liquids you can think of?

Milk, oil, juice, ink and honey.

Have you ever noticed that you can smell the food being cooked even without entering the kitchen? How does this smell reach us?

The smell spreads through the air and reaches our nose.

What are the other examples of gases you can think of? What about oxygen and carbon dioxide?

Oxygen, carbon dioxide, nitrogen and water vapour are examples of gases.

5. How Can We Change the States of Water?

How can you change the state of water?

We can change the state of water by heating or cooling it.

How can you quickly change ice to its liquid state, water?

Heat the ice. It melts and changes into water.

If we have to change ice into water, and water into water vapour, we have to supply heat to it. If we want to change water into ice, what should be done?

Water should be cooled, for example, by keeping it in a freezer.

Can you think of any other example, besides water, that can change from solid to liquid?

Candle wax can change from solid to liquid when heated.

How can we turn candle wax into liquid state? How can we change the liquid wax back into solid state?

Heat the candle wax to make it liquid. Cool the liquid wax to make it solid again.

What are the other liquids you have seen which get converted into a solid?

Coconut oil, butter and ghee can become solid when cooled.

Have you ever seen coconut oil getting converted into its solid state during the winter season?

Yes. Coconut oil can become semi-solid or solid during cold weather.

Melting: Conversion of a solid into a liquid state.
Freezing: Conversion of a liquid into a solid state.

Activity 8.6: Let us complete the diagram

Conversion of different states of water:

Change	Process
Solid → Liquid	Melting
Liquid → Solid	Freezing
Liquid → Gas	Evaporation
Gas → Liquid	Condensation

6. How Can Water Be Evaporated Faster or Slower?

What are the conditions that affect how fast water evaporates?

Exposed surface area, temperature, movement of air and humidity affect evaporation.

What differences do you see in evaporation on a cold day versus a hot day?

Water evaporates faster on a hot day and slower on a cold day.

Activity 8.7: Let us investigate

What conditions did we keep the same?

The amount of water and the surrounding conditions are kept as similar as possible.

What did we change in this investigation?

We changed the exposed surface area of water.

What did we measure?

We measured the time taken for the water to completely evaporate.

What can you conclude from this investigation?

Water evaporates faster when a larger surface area is exposed to air.

What would happen if milk is taken instead of water in the above activity?

Milk would also evaporate, but it may leave some substances behind because milk contains dissolved substances.

Factors affecting evaporation:

Larger exposed surface area → faster evaporation
Higher temperature → faster evaporation
More air movement → faster evaporation
Higher humidity → slower evaporation

Activity 8.8: Let us explore

What conclusions can you draw from Activity 8.8 and other similar experiences?

Water evaporates faster in sunlight and on hot days. Moving air also makes evaporation faster.

Do clothes dry faster or slower on a windy day?

Clothes dry faster on a windy day because moving air increases evaporation.

If you want to dry your clothes on a rainy day, how can you make it faster?

Keep the clothes in a well-ventilated place, spread them out and use a fan if possible.

7. Cooling Effect

Why is the water in the earthen pot so cold? I never observed water getting cold in a stainless steel pot. What do you think is the reason?

Some water seeps through the tiny pores of the earthen pot and evaporates. Evaporation produces a cooling effect.

What are the other examples of cooling effect?

Sprinkling water on floors or roofs in summer and sweating are examples of cooling by evaporation.

How do you feel when you rub sanitiser on your hands?

Our hands feel cool because the sanitiser evaporates and takes heat from the skin.

Pot-in-pot cooler: evaporation of water from the moist sand produces cooling.

Activity 8.9: Let us make a model

Pot-in-pot cooler:

Take two earthen pots of different sizes.
Put sand at the bottom of the larger pot.
Place the smaller pot inside it.
Fill the gap with sand.
Pour water into the sand.
Cover the smaller pot with a lid or wet jute sack.
Allow 4–5 hours for cooling.

For how many days can the vegetables and fruits be kept fresh in it?

It depends on temperature, humidity, the type of food and how moist the sand remains. Observe and record the result.

What are the conditions which can affect the number of these days?

Temperature, humidity, ventilation, amount of water and type of food can affect it.

What else can be used in place of sand for better cooling?

Other porous materials that can hold water may be tested, but sand is commonly used because it holds moisture well.

8. How Do Clouds Give Us Rain?

Water vapour rises into the atmosphere. At higher and cooler levels, it condenses into tiny droplets around dust particles. These droplets form clouds. When many droplets join and become heavy, they fall as rain.

Why does air containing water vapour go up in the atmosphere?

Water vapour is lighter than air, so it rises upward.

If you want to dry your clothes on a rainy day, how can you make it faster?

Spread the clothes properly and keep them where there is good air movement. A fan can also help.

The water cycle: evaporation, condensation and precipitation.

Complete the poem

I wonder, oh! I wonder so,
Which path does water choose to go?
I wonder, oh! I wonder so,
When does it snow?
I wonder, oh! I got a wonder call,
How does rain fall?

Possible completion:

Water rises as vapour high,
Condenses to clouds across the sky.
Droplets join and become rain,
And water reaches Earth again.

Activity 8.10: Let us engage in a group activity

What will you observe?

After adding the burnt newspaper and squeezing the bottle, some haziness or cloud-like formation can be observed above the water.

What role do the tiny dust particles play?

Water vapour condenses around tiny particles and forms small water droplets.

9. Water Cycle

Water cycle: The continuous circulation of water between the Earth’s surface and the atmosphere is called the water cycle.

Activity 8.11: Let us understand the process

Label Fig. 8.9 using arrows shown and the words given in the box to show where water is stored, how water changes its state and where it moves.

The important labels are: Cloud, Lake, Ocean, River, Groundwater, Evaporation, Condensation, Rain and Snow.

Water cycle in simple steps:

Water evaporates from oceans, lakes and Earth’s surface.
Water vapour rises into the atmosphere.
Water vapour cools and condenses to form clouds.
Water falls as rain, hail or snow.
Water flows into rivers, lakes, groundwater and oceans.
The cycle continues.

What did I do well?

I was able to understand and label the main parts of the water cycle.

Was I able to label all the parts of the water cycle?

Yes, I can label the main parts such as evaporation, condensation, rain, clouds, rivers, lakes, ocean and groundwater.

Which parts of the water cycle were unclear to me?

This depends on my understanding. I can ask my teacher about any step that I find difficult.

10. Easy Concepts to Remember

Water exists as solid, liquid and gas.
Ice is the solid state of water.
Water is the liquid state.
Water vapour is the gaseous state.
Solid changes to liquid by melting.
Liquid changes to solid by freezing.
Liquid changes to gas by evaporation.
Gas changes to liquid by condensation.
Evaporation causes cooling.
Heat makes evaporation faster.
Moving air makes evaporation faster.
Larger exposed area makes evaporation faster.
High humidity slows evaporation.
Clouds form when water vapour condenses.
Rain, hail and snow return water to Earth.
The continuous movement of water is called the water cycle.

11. Summary

The process of conversion of water into its vapour state is called evaporation.
The process of conversion of water vapour into its liquid state is called condensation.
Water is found in different states—solid, liquid and gas.
Water changes its state on heating or cooling.
Conditions which make the evaporation faster or slower are exposed area, humidity, air movement, etc.
Evaporation causes cooling effect.
Water vapour condenses to form tiny droplets of water, which appear as clouds.
Many tiny water droplets come together and fall down as rain, hail or snow.
The circulation of water between the Earth surface and atmosphere is known as the water cycle.
Observation, questioning, possible reasons and experiments help us understand evaporation and condensation.

12. Keywords

Experiment Record Observe Investigate Reason Question Predict Condensation Freezing Evaporation Gas Solid Liquid Water cycle Water vapour Melting Humidity

13. Let Us Enhance Our Learning – Book Solutions

1. Which of the following best describes condensation?
(i) The conversion of water into its vapour state.
(ii) The process of water changing from a liquid into gaseous state.
(iii) The formation of clouds from tiny water droplets.
(iv) The conversion of water vapour into its liquid state.

Answer: (iv) The conversion of water vapour into its liquid state.

2. Identify in which of the given processes, evaporation is very important—
(i) Colouring with
(a) crayons (b) water colours (c) acrylic colours (d) pencil colours
(ii) Writing on paper with
(a) pencil (b) ink pen (c) ball point pen

Answer:
(i) (b) water colours
(ii) (b) ink pen

3. We see green coloured plastic grass at many places these days. Space around natural grass feels cooler than space around the plastic grass. Can you find out why?

Natural grass contains water. Water evaporates from the grass and causes cooling. Plastic grass does not provide the same evaporative cooling.

4. Give examples of liquids other than water that evaporate.

Examples include alcohol, sanitiser and perfume.

5. Fans move air around, creating a cooling sensation. It might seem strange to use a fan to dry wet clothes since fans usually make things cooler, not warmer. Normally, when water evaporates, it requires heat, not cold air. What do you think about this?

A fan moves air over wet clothes. Moving air carries away water vapour, so more water can evaporate. Evaporation uses heat from the surroundings and helps the clothes dry.

6. Usually, when sludge is removed from drains, it is left in heaps next to the drain for 3–4 days. Afterward, it is transported to a garden or a field where it can be used as manure. This approach reduces transportation cost of the sludge and enhances the safety of individuals handling it. Reflect upon it and explain how.

Leaving sludge in the open allows some water to evaporate. The sludge becomes lighter and easier to transport. It also becomes easier and safer to handle.

7. Observe the activities in your house for a day. Identify the activities that involve evaporation. How does understanding the process of evaporation help us in our daily activities?

Examples include drying clothes, drying utensils, drying a mopped floor, sweating and using sanitiser. Understanding evaporation helps us dry things faster and understand cooling.

8. How is water present in the solid state in nature?

Water is present as ice and snow in glaciers, ice caps, mountains and very cold regions.

9. Reflect on the statement “Water is our responsibility before it is our right.” Share your thoughts.

We all depend on water, so we should use it carefully. We should avoid wasting water, prevent pollution and protect water sources for present and future generations.

10. The seat of a two-wheeler parked on a sunny day has become very hot. How can you cool it down?

Cover the seat with a wet cloth or sprinkle a little water on it. As the water evaporates, it takes heat away and cools the seat.

14. Learning Further – Easy Answers

Wet one hand with water and leave the other dry. Blow air across both hands and feel the cooling effect. Find out the reasons for it.

The wet hand feels cooler because water evaporates from it. Evaporation takes heat from the hand and produces a cooling effect.

Make a game to navigate through different states of water and water related concepts to reach the finish line. Challenge cards with questions related to water cycle, evaporation, condensation, etc., can be some game elements.

Activity idea: Make a board with three sections—Solid, Liquid and Gas. Players move forward by answering questions about melting, freezing, evaporation, condensation and the water cycle.

Discuss with your teacher and act out the stages of the water cycle through a role-playing activity in your school assembly.

Activity idea: Students can act as the Sun, water, water vapour, clouds, rain, rivers and oceans to show evaporation, condensation, rainfall and collection of water.

15. Quick Revision

Question	Answer
Solid state of water	Ice
Liquid state of water	Water
Gaseous state of water	Water vapour
Solid → Liquid	Melting
Liquid → Solid	Freezing
Liquid → Gas	Evaporation
Gas → Liquid	Condensation
Continuous movement of water	Water cycle
Amount of water vapour in air	Humidity
Evaporation produces	Cooling effect

“`1 Download Class 6 Science Chapter 8 Notes PDF

Practice Class 6 Science Chapter 8 Looking for extra practice? Use the worksheet below to revise Chapter 8 with easy questions, extra practice questions and revision exercises.