A Journey through States of Water

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

 

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

Activity 8.1: Let us observe

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

Ice gets converted into water.

What can you conclude from the observations?  

Does this mean that ice and water are the same substance? Yes, ice and water are the two forms of the same substance. These forms are also called states. These different states of water show many differences in their behaviour. Water flows but ice does not. Water splashes but ice does not. 

It is a rainy morning. 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 in the puddles disappearing? Where does it go? Discuss with your friends.

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

You might have observed that after washing the utensils, water left on the surface of the utensils, dries up after some time. Does the reason you thought earlier to explain water disappearance apply in this case also? 

Aavi wonders if water has seeped through the surface of the utensils. 

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 as shown in Fig. 8.1. 
• Observe whether water seeps through to the other side of the plate or not.
• Keep observing this at regular intervals 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? 

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

 This water gets converted into gaseous state called water vapour. The water vapour is another state of water. Let us think of another observation where you notice the water disappearing. 

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

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. After a few minutes, they notice something exciting about the outer surface of the glass tumbler. 

Let us find out by conducting a similar activity ourselves. 

• 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 feel if there is any change.
  

You may have many observations and questions here.  

Table 8.1: Record the observations and questions  

Aavi and Thirav conduct an activity to find evidence for their reasons. You can also conduct the activity by following the steps given below. Record your data in Table 8.2. 

• 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.
• Observe the reading on the balance and record the weight after every five minutes.
• Continue observing for 30 minutes. 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? 

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

You may observe some water droplets on the glass tumbler. Water vapour from the air comes in contact with the cold surface of the glass tumbler and gets converted into water droplets on the glass tumbler through condensation. There is an increase in the reading on the digital weighing balance. Can we conclude that water is not seeping through the wall of the tumbler? Can we also conclude that the water collected outside the tumbler is only due to condensation? No, we cannot say that conclusively from Activity 8.4. What more can you do to show that water is not seeping from the glass tumbler? How would you modify Activity 8.4 to find the answer? 

Repeat Activity 8.4 with the following modifications—  

• Mark the water level on the glass tumbler with a permanent marker or a visible tape.  
  

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? This activity shows that water is not seeping from the glass tumbler and the extra water is getting collected because of condensation.

Water is a substance that can be observed in three different states in our daily life. In the solid state, it exists as ice. 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. 

• Put an ice cube in one container and transfer it to another container of different shape. What changes do you notice in the shape of the ice cube? Record your observations in Table 8.3.
• Pour water from one container to another container of a different shape. Observe how water behaves compared to the ice cube and make a record. Did you notice how water flows from one container to the other? 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.  
  

So far we have learnt that water can exist in solid, liquid and gaseous states. How can you change the state of water? How can you quickly change ice to its liquid state, water?

Fill up the blank boxes in Fig. 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. Two words have been filled for you. 

In section 8.1, we have learnt about evaporation. Let us explore it more! 

Observe your surroundings. What are the conditions that affect how fast water evaporates? What differences do you see in evaporation on a cold day versus a hot day? Discuss with your friends. The following words may help in your discussion—fan, drying cloth, sweating, windy day, hot day, rainy day. 

Let us perform Activity 8.7 to investigate conditions that will affect how fast water will evaporate.  

• 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

Table 8.4: Findings of the investigation  

Condensation plays a significant role in the process of bringing evaporated water back to the Earth’s surface. How does this happen? When air moves higher above the Earth’s surface, it becomes cooler and cooler. At certain heights, the air gets so cool that the water vapour in it turns into droplets which are generally formed around dust particles. 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. These falling water drops are what we call rain. 

 

Activity 8.10 demonstrates the role of dust particles in the formation of clouds.  

• Take an empty discarded one litre plastic bottle. Pour about one cup of water into it. 
• Close the lid tightly. Now quickly squeeze and release 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. 

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 water from the ocean and the Earth’s surface evaporates into the atmosphere as vapour and returns as rain, hail or snow, ultimately flowing back to the oceans. This circulation of water is known as the water cycle.

  Only a small portion of water available on the Earth is fit for use by plants, animals and humans. 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. Hence, it is very important to use water wisely and avoid wasting it. Let us keep our water bodies free from pollution. You will learn more about water and its conservation in the chapter ‘Nature’s Treasures’