Textbook-based subjective questions

On a bright summer afternoon, Aavi and Thirav enjoy their shikanji (lemonade).

So, they must be different substances.

Activity 8.1: Let us observe Put an ice cube in a cup, leave it on the table and observe. What can you conclude from the observations?

Yes, ice and water are the two forms of the same substance. These different states of water show many differences in their behaviour.

While going to school, Aavi and Thirav observe that there are a lot of water puddles in the playground. That evening, when they go to play, they are surprised to observe that some of the water in the puddles had disappeared. Have you ever noticed water I think the water has in the puddles disappearing? been absorbed by the soil on Where does it go?

Have you ever noticed water I think the water has in the puddles disappearing? been absorbed by the soil on Where does it go? What do you your friends. think about it? Where else have you seen water disappearing?

Can you think of a possible reason why this happens?

to explain water disappearance apply in this case also?

Design an activity to investigate whose idea is correct. Activity 8.2: Let us investigate Take a tablespoon of water on a steel plate as shown in Fig.

Is this activity enough to come to the conclusion that water does not seep through a steel plate? If water does not seep through the steel plate.

This water gets converted into gaseous state called water vapour. 8.1: Steel plate with another state of water. Let us think of another a tablespoon of water observation where you notice the water disappearing.

While making dosa, we sprinkle some water on the hot pan and it disappears. Water vapour is actually invisible Let us draw but the Draw a detailed sketch (with labels and presence of caption) about what happens to the water. tiny droplets of water in the The water which is sprinkled on the hot steam makes it pan gets converted into steam. Steam is visible. actually water vapour, some part of which Do you converts into water droplets. know?

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

Can you think of other examples of evaporation?

Is it due to: (i) seeping of water into the ground or (ii) evaporation of water or (iii) both of these? Hand sanitiser disappears as you rub it on your hands.

8.2 Another Mystery Next day, Aavi, Thirav and their friends decide to make lemonade. During the preparation, they take cold water in a glass tumbler and add ice cubes into it.

Let us find out by conducting a similar activity ourselves. Activity 8.3: Let us experiment Take cold water in a glass tumbler. Add a few ice cubes into it as shown in Fig. 8.2. Leave it undisturbed for five minutes and observe it. Record your observations and the questions that arise in your mind in Table 8.1.

You can also touch the outer surface of the glass tumbler to Fig. 8.2: A glass tumbler containing cold water and ice cubes feel if there is any change. You may have many observations and questions here.

You may have many observations and questions here.

You may be curious about where the water droplets come from.

You may agree or disagree with the reasons of others. Aavi and Thirav argued with a chain of reasons.

What do you think about the possible reasons mentioned in Fig. I think that some of the water may have seeped out of the glass No, it cannot seep tumbler. out.

It might have decreased, but may With a tall and narrow not be significant bottle, even a slight change enough to be seen. We can take water at room temperature in another tumbler and find out whether any water seeps out. Continue the discussion on the given reasons or conduct activities to find evidence for the reasons given to help in this discussion.

Continue the discussion on the given reasons or conduct activities to find evidence for the reasons given to help in this discussion. Where else have you seen water droplets like this? You might have seen dew drops on plants.

Why do we see dew drops more in the morning?

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

Could the water appearing on the outer surface of the glass tumbler in Activity 8.3 also be due to condensation of water vapour present in the air? Activity 8.4: Let us measure Aavi and Thirav conduct an activity to find evidence for their reasons.

Record your data in Table 8.2. Take a glass tumbler half-filled with water containing a few ice cubes. Weigh it on a digital weighing balance.

Record your observations in Table 8.2. 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?

Will it increase or decrease or remain the same? Do your findings match with your predictions? The amount of water vapour in You may observe some water the air is also known as humidity. droplets on the glass tumbler.

The daily humidity data for your area is reported in the Water vapour from the air newspapers and other sources. comes in contact with the cold Compile the data for the year and More to surface of the glass tumbler study any patterns, if present. and gets converted into water do! droplets on the glass tumbler through condensation.

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

What more can you do to show that water A Journey through States of Water is not seeping from the glass tumbler?

Repeat Activity 8.4 with the following modifications— Mark the water level on the glass tumbler with a permanent marker or a visible tape. Water level in the glass tumbler does not go down but the extra water gets collected on the outer surface of the glass tumbler.

This activity shows that water is not seeping from the glass tumbler and the extra water is getting collected because of condensation. 8.3 What are the different States of Water? Water is a substance that can be observed in three different states in our daily life.

On heating, the ice melts and gets converted into its liquid state. On further heating, water gets converted into its gaseous state. Let us perform Activity 8.5 to identify the properties of different states of water.

Activity 8.5: Let us identify Put an ice cube in one container and transfer it to another container of different shape.

Record your observations in Table 8.3. Pour water from one container to another container of a different shape.

What happens to its shape? Pour water on a clean surface and observe how it spreads. When water gets converted into water vapour, how does this water vapour spread? Compare this with the spreading behaviour of water.

What are the differences in the properties of water in solid, liquid and gaseous states? Ice (solid state) retains its shape irrespective of the container in which it is placed while water takes the shape of the container.

It takes up the shape of the container in which it is kept, but the volume of water remains constant. Does water also possess the property to spread? Yes, water also has the property to spread while keeping the volume constant.

Water vapour (gaseous state) exhibits a property of spreading out in the entire available space. Water vapour exists even at room temperature; though it is invisible to us. The water that evaporates during processes like drying of clothes or mopping of floors contribute to the water vapour in the air around us.

The water that evaporates during processes like drying of clothes or mopping of floors contribute to the water vapour in the air around us.

Let us look at some more examples of solids, liquids and gases.

What are the other examples of liquids you can think of? Have you ever noticed that you can smell the food being cooked even without entering the kitchen?

It is because the smell of yummy food from cooking spreads through the air and reaches our nostrils, even if we are not in the kitchen. What are the other examples of gases you can think of?

So far we have learnt that water can exist in solid, liquid and gaseous states. How can you change the state of water? Atmospheric Water Generator (AWG) How can you quickly change ice machines collect water from humid air to its liquid state, water? to produce drinkable water.

Atmospheric Water Generator (AWG) How can you quickly change ice machines collect water from humid air to its liquid state, water? to produce drinkable water. This is done If we have to change ice into through condensation of water vapour water, and water into water by cooling the air. This process vapour, we have to supply is similar to the formation of heat to it.

If we want to change drops of water outside the water into ice, what should be glass tumbler filled with ice done?

If we take the ice out of the freezer, it melts and is converted into water.

A candle, which is made of wax, is one such example. How can we turn candle wax into liquid state?

We should cool the liquid wax to change it into a solid. What are the other liquids you have seen which get converted into a solid?

Hence, we can see that water and other substances change their states on heating or cooling. The process of conversion of a solid into liquid state is called melting. The process of conversion of liquid into solid state is called freezing.

The process of conversion of liquid into solid state is called freezing. Let us check the connection between different states of water through Activity 8.6. Activity 8.6: Let us complete the diagram

8.5 marked as A, B, C and 1, 2, 3, 4 for conversion of different states of water using the words given in the box.

8.5 How can Water be Evaporated Faster or Slower?

What differences do you see in evaporation on a cold day versus a hot day? The following words may help in your discussion—fan, drying cloth, sweating, windy day, hot day, rainy day.

Activity 8.7: Let us investigate Take water in a small cap of a bottle (you may use sanitiser in place of water). Take the same amount of water in a plate. The exposed area of water in the bottle cap and the plate are different. Keep both of them near each other. Record the time taken for the water to completely evaporate in each case in Table 8.4.

What What conditions did did we change in What did we we keep the same? this investigation? measure? Reflect on what you Time taken for Exposed area of water did really complete evaporation well in this activity. What can you conclude from this investigation?

If you spread out water on a plate, its area exposed to air is larger. What would happen if milk is taken instead of water in the above activity? Other conditions which affect how fast water evaporates Design an activity similar to Activity 8.7 to find out what are the other conditions which can affect how fast water will evaporate.

Perform this activity, use Table 8.5 to record the data and discuss your observations.

Other than the conditions you have explored to find how water can be made to evaporate faster or slower, you can also conduct Activity 8.8 to explore it further.

What conclusions can you draw from Activity 8.8 and other similar experiences? Water evaporates faster from the cap kept in sunlight compared to the cap kept in shade. It is a common observation that clothes dry faster on a hot sunny day.

Do clothes dry faster or slower on a windy day? It is once again a common observation that clothes dry faster on a windy day.

It is also a common observation that clothes dry slowly on a The amount of water rainy day. On a rainy day, water vapour in the air is evaporates slowly. If the amount more on rainy days of water in the air is already and hence rainy days high (more humidity), water are more humid. evaporates slowly.

Do you If you want to dry your clothes on a know? rainy day, how can you make it faster? 8.6 Cooling Effect Aavi’s mother purchased a new matka (earthen pot) to replace the stainless steel pot for storing drinking water. Upon returning from school, Aavi notices the earthen pot and drinks water from it.

Upon returning from school, Aavi notices the earthen pot and drinks water from it.

Water seeps through the surface of the Now, I can understand earthen pot and evaporates, which imparts why we feel cooler if we sit a cooling effect on the water.

How do you feel when you rub sanitiser on your hands? Let us perform Activity 8.9 to observe the cooling effect by making a simple and electricity-free model of pot-in-pot

Activity 8.9: Let us make a model Take two earthen pots of different sizes. Fill the bottom of the larger pot with a layer of sand. Place the smaller pot into the centre of the larger one as shown in Fig. 8.7. Fill the gap between the pots with more sand. Pour water in the sand area.

Large pot You can also make a drawing of the Lid 8.7: A pot-in-pot cooler Allow 4–5 hours for the mini pot-in-pot cooler to cool down. The time range can be influenced by many conditions.

The time range can be influenced by many conditions. Observe and discuss how it creates a cooling effect inside the pots. Keep some vegetables and fruits in it and observe for a week on a daily basis to check for the freshness of the vegetables and fruits kept inside the cooler.

You will have to add water regularly to keep the sand moist.

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

In summers, surahi is used to keep the water cold. Condensation plays a significant role in the process of bringing Why does air containing evaporated water back to the water vapour go up in the Earth’s surface.

When air moves that surrounds the Earth)? higher above the Earth’s As we know, gas balloons surface, it becomes cooler and containing lighter gases go A Journey through States of Water At certain heights, the up in the air.

These small droplets float in the air and form clouds. Many droplets join together to form bigger drops of water. Some drops get so heavy that they start falling.

Some drops get so heavy that they start falling. These falling water drops are what we call rain. Under special conditions, it might also fall as hail or snow.

Aavi enjoys the rain and creates a poem.

I wonder so, Which path does water choose to go?

Activity 8.10 demonstrates the role of dust particles in the formation of clouds. Activity 8.10: Let us engage in a group activity Take an empty discarded one litre plastic bottle.

Handle burning Close the lid tightly. Now quickly squeeze and release paper carefully. the bottle continuously for about 2–3 minutes.

Observe the space above the water in the bottle. Repeat the same activity after adding a small burnt piece of newspaper into the water. What will you observe? In this case, you will observe some haziness (clouds) above the water in the bottle. The burnt newspaper provides very small invisible dust particles, around which water vapour condenses and forms clouds. Let us perform Activity 8.11 to represent our understanding of how water changes its state and its movement.

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. 8.9: Change of states and movement of water Was I able to label all the parts of the water

The water from the ocean and the Earth’s cycle?

This circulation of water is known as the water cycle.

Most of the water is in the oceans and it cannot be used directly. We use water for drinking and also for many other activities.

The number of people using water is increasing with a rise in population. The increasing demand for water causes its shortage in many parts of the world.

Let us keep our water bodies free from pollution. You will learn more about water and its conservation in the chapter ‘Nature’s Treasures’. 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.

The water vapour in the air 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. We have used the process of observation, questioning, possible reason and experimenting to find out the concepts of evaporation and condensation. Which of the following best describes condensation?

Which of the following best describes condensation?

(iii) The formation of clouds from tiny water droplets.

We see green coloured plastic grass at many places these days. Space around natural grass feels cooler than space around the plastic grass.

Give examples of liquids other than water that evaporate. Fans move air around, creating a cooling sensation.

Normally, when water evaporates, it requires heat, not cold air. 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

Afterward, it is transported to a garden or a field where it can be used as This approach reduces transportation cost of the sludge and enhances the safety of individuals handling it. Observe the activities in your house for a day.

Identify the activities that involve evaporation.

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

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