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.
- •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?
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? You might have observed that after washing the utensils, water left on the surface of the utensils, dries up after some time.
Water does not seep through the steel plate. The water gets converted into gaseous state called water vapour. The water vapour is another state of water.
- •Take a tablespoon of water on a steel plate (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.
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.
There are water droplets (tiny drops) appearing on the outer surface of the glass tumbler. Initially, water droplets are deposited and these droplets combine together to form bigger drops.
- •Take cold water in a glass tumbler.
- •Add a few ice cubes into it (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.
Table 8.1: Record the observations and questions
| I observe | I wonder |
|---|---|
You might have seen dew drops on plants. Why do we see dew drops more in the morning? 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. These water drops come from condensation of water vapour.
Water vapour from the air comes in contact with the cold surface of the glass tumbler and gets converted into water droplets through condensation. There is an increase in the reading on the digital weighing balance. Modify this activity by marking the water level inside the tumbler — water level inside does not go down but extra water gets collected outside because of condensation.
- •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?
Table 8.2: Measurement of mass in condensation experiment
| Time | Mass of water |
|---|---|
| 0 min | |
| 5 min | |
| 10 min | |
| 15 min | |
| 20 min | |
| 25 min | |
| 30 min |
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.
- •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. 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.
Table 8.3: Compare different states of water
| Property | Ice (Solid state) | Water (Liquid state) | Water vapour (Gaseous state) |
|---|---|---|---|
| Shape | |||
| Ability to flow | |||
| Ability to spread | |||
Ice (solid state) retains its shape irrespective of the container in which it is placed while water takes the shape of the container. Ice does not flow or spread. Water (liquid state) flows and changes its shape. Water does not have a fixed shape. It takes up the shape of the container in which it is kept, but the volume of water remains constant. 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. Gases do not possess a fixed shape. Water vapour exists even at room temperature though it is invisible to us.
Some other substances also exhibit these states. For example, wax, oil and ghee. Compare examples of solids (stones, wood, glass), liquids (milk, oil), and gases (oxygen, carbon dioxide).
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, it can be done by placing water in a cold environment, such as a freezer. Water freezes and is converted into ice.
- •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.
- •Words to use: Liquid, Freezes, Evaporates, Gas, Condenses
- •Two words have been filled for you: A = Solid, 1 = Melts
- •B = [Liquid], C = [Gas], 2 = [Evaporates], 3 = [Freezes], 4 = [Condenses]
Let us explore the conditions that affect how fast water evaporates. What differences do you see in evaporation on a cold day versus a hot day? Discussion words: fan, drying cloth, sweating, windy day, hot day, rainy day.
If you spread out water on a plate, its area exposed to air is larger. Therefore, evaporation is faster.
- •Take water in a small cap of a bottle.
- •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.
- •Think: What conditions did we keep the same? What did we change? What did we measure?
Table 8.4: Findings of the investigation (exposed area vs. evaporation)
| Exposed area of water | Time taken for complete evaporation |
|---|---|
| Less (bottle cap) | |
| More (plate) |
Water evaporates faster from the cap kept in sunlight compared to the cap kept in shade. Clothes dry faster on a hot sunny day. With the increase in the movement of air (wind), water evaporates faster. On a rainy day (high humidity), water evaporates slowly.
- •Take identical caps of two bottles.
- •Pour equal amount of water in each cap.
- •Place one cap in sunlight and keep the other in shade (Fig. 8.6).
- •Observe the two caps after every 15 minutes.
- •Record the time taken for the water to completely evaporate in each case.
- •You can also repeat this activity on a windy or a rainy day, and record your observations.
Table 8.5: Record data of investigation with one condition changed
| Condition that is changed | Time taken for complete evaporation |
|---|---|
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. Why is the water in the earthen pot so cold? Water seeps through the surface of the earthen pot and evaporates, which imparts a cooling effect on the water. Sprinkling water on the floor or the roof during summer to cool it is another example of evaporation's cooling effect.
Allow 4-5 hours for the mini pot-in-pot cooler to cool down. You will have to add water regularly to keep the sand moist. This traditional clay pot is called a Surahi and is used in summers to keep water cold.
- •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 (Fig. 8.7).
- •Fill the gap between the pots with more sand.
- •Pour water in the sand area.
- •Place a lid or wet jute sack to cover the top of the smaller pot.
- •Observe and discuss how it creates a cooling effect inside the pots.
- •Keep some vegetables and fruits in it and observe for a week to check for freshness.
Condensation plays a significant role in the process of bringing evaporated water back to the Earth's surface. 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.
Under special conditions, water may also fall as hail or snow.
- Handle burning paper carefully.
- •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.
- •In the second 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.
- •Label Fig. 8.9 using arrows and the words given in the box to show where water is stored, how water changes its state and where it moves.
- •Words to use: Cloud, Lake, Ocean, River, Groundwater, Evaporation, Condensation, Rain, Snow
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. 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.
Keywords
- 1The process of conversion of water into its vapour state is called evaporation.
- 2The process of conversion of water vapour into its liquid state is called condensation.
- 3Water is found in different states—solid, liquid and gas.
- 4Water changes its state on heating or cooling.
- 5Conditions which make the evaporation faster or slower are exposed area, humidity, air movement, etc.
- 6Evaporation causes a cooling effect.
- 7The 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.
- 8The circulation of water between the Earth surface and atmosphere is known as the water cycle.
- 9We have used the process of observation, questioning, possible reason and experimenting to find out the concepts of evaporation and condensation.
- 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.
