CBSE Class 6- Science Chapter 8: A Journey through States of Water – Study Notes (PDF)

Study Notes: A Journey through States of Water (Class 6-NCERT(Curiosity) Science

1. Introduction: The Nature of Water and Ice

Water is a substance that can be observed in different forms, also known as states. The text begins with a discussion between two characters, Aavi and Thirav, about whether ice and water are the same substance. While ice feels hard and can be held, and water flows and cannot be held in the same way, they are ultimately two different forms of the same substance. An experiment of placing an ice cube in a cup and observing it melt into water confirms this relationship.

• Ice: The solid state of water. It is hard, does not flow, and does not splash.
• Water: The liquid state of water. It flows, splashes, and takes the shape of its container.

2. Evaporation: Water’s Disappearing Act

The phenomenon of water seemingly disappearing from surfaces like puddles, washed utensils, or a hot pan is explained by the process of evaporation.

• Definition: Evaporation is the process of conversion of water (liquid) into its vapour state (gas).
• Water Vapour: The gaseous state of water. It is generally invisible.
• Steam: Steam is water vapour, which becomes visible due to the presence of tiny droplets of condensed water within it.
• Continuous Process: Evaporation occurs continuously, even at room temperature.
• Examples:
  • Drying of wet clothes.
  • Drying of a mopped floor.
  • Drying of sweat from the body.
  • Disappearance of hand sanitiser when rubbed on hands.
  • Water from puddles disappears due to a combination of evaporation and seeping into the ground.

3. Condensation: The Formation of Water Droplets

When a glass tumbler is filled with cold water and ice, tiny water droplets appear on its outer surface. This phenomenon is caused by condensation.

• Definition: Condensation is the process of conversion of water vapour into its liquid state.
• Mechanism: Water vapour, which is always present in the air, comes into contact with a cold surface (like the outside of the glass). This cooling causes the vapour to change back into liquid water droplets.
• Experimental Proof:
  • An experiment shows that the level of water inside the glass does not decrease, and the total mass of the glass with water increases over time. This proves the water is not seeping out but is being added to the outside from the air.
• Examples:
  • Dew drops seen on plants, especially in the morning.
  • Water drops accumulating on the inner side of a steel plate used to cover a utensil of boiling water.

4. The Three States of Water and Their Properties

Water can exist in three different states: solid, liquid, and gas. Each state has distinct properties. Other substances, like wax, oil, and ghee, also exhibit these states.

Property	Ice (Solid State)	Water (Liquid State)	Water Vapour (Gaseous State)
Shape	Retains its shape; does not change with the container.	Takes the shape of the container. Has no fixed shape.	Spreads out to fill the entire available space. Has no fixed shape.
Ability to Flow	Does not flow.	Flows from one container to another.	Flows and spreads through the air.
Ability to Spread	Does not spread.	Spreads on a surface, but its volume remains constant.	Spreads out to fill the entire available space.

• Examples of Solids: Stones, wood, glass.
• Examples of Liquids: Milk, oil.
• Examples of Gases: Oxygen, carbon dioxide, the smell from cooking food which spreads through the air.

5. Changing the States of Water

The state of water and other substances can be changed by heating or cooling.

• Melting: The process of converting a substance from a solid state to a liquid state by supplying heat. (e.g., Ice melting into water).
• Freezing: The process of converting a substance from a liquid state to a solid state by cooling. (e.g., Water freezing into ice in a freezer).
• Evaporation: The process of converting a substance from a liquid state to a gaseous state by supplying heat. (e.g., Water turning into water vapour).
• Condensation: The process of converting a substance from a gaseous state to a liquid state by cooling. (e.g., Water vapour turning into liquid water).

Cycle of State Changes: Solid (Ice) → (Melts) → Liquid (Water) → (Evaporates) → Gas (Water Vapour) → (Condenses) → Liquid (Water) → (Freezes) → Solid (Ice)

6. Factors Affecting the Rate of Evaporation

The speed at which water evaporates can be influenced by several conditions.

• Exposed Surface Area: Evaporation is faster when the surface area exposed to the air is larger. Water in a plate evaporates faster than the same amount of water in a bottle cap.
• Temperature (Heat): Evaporation is faster on a hot, sunny day. Water evaporates more quickly when placed in direct sunlight compared to the shade.
• Air Movement (Wind): Evaporation is faster on a windy day. The movement of air helps carry away the water vapour, allowing more water to evaporate. This is why clothes dry faster on a windy day.
• Humidity: Humidity is the amount of water vapour in the air. Evaporation is slower when the humidity is high (e.g., on a rainy day) because the air is already saturated with water vapour.

7. The Cooling Effect of Evaporation

Evaporation has a cooling effect because the process requires heat energy from the surrounding environment.

• Earthen Pots (Matka/Surahi): Water stored in earthen pots remains cool because water seeps through the tiny pores of the pot and evaporates from the outer surface, drawing heat from the water inside and thus cooling it.
• Other Examples:
  • Sprinkling water on a roof or floor during summer cools the surface.
  • Hand sanitiser feels cold when rubbed on the hands as it evaporates quickly.
  • We feel cooler under a fan because the moving air increases the rate of evaporation of sweat from our skin.
• Pot-in-Pot Cooler: A simple, electricity-free refrigerator model made of two earthen pots and sand. Water poured into the sand between the pots evaporates, creating a cooling effect in the inner pot, which can keep vegetables and fruits fresh.

8. The Water Cycle: Cloud Formation and Rain

Evaporation and condensation are key components of the water cycle, which describes the continuous movement of water on, above, and below the surface of the Earth.

1. Evaporation: Water from oceans, lakes, rivers, and the Earth’s surface heats up and evaporates, turning into water vapour. Being lighter than air, this water vapour rises into the atmosphere.
2. Condensation & Cloud Formation: As the air containing water vapour moves higher, it cools down. At certain heights, the air becomes so cool that the water vapour condenses back into tiny liquid water droplets, typically forming around invisible dust particles in the air. These clusters of small droplets float in the air and form clouds.
3. Precipitation: Many of these tiny droplets join together to form bigger, heavier drops of water. When these drops become too heavy to float, they fall back to Earth as rain. Under special, colder conditions, this precipitation can also fall as hail or snow.
4. Collection: The fallen water flows back into rivers, lakes, and oceans, or seeps into the ground (groundwater), completing the cycle.

Water Conservation: Only a small portion of Earth’s water is freshwater fit for use. Due to increasing population and demand, it is crucial to use water wisely, avoid wastage, and keep water bodies free from pollution.

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Quiz Section

Part A: Short-Answer Questions (25 Questions)

(Answer in 2-3 sentences)

1. Explain why ice and water are considered two different states of the same substance.
2. What is evaporation? Provide two examples from daily life.
3. Describe the process of condensation.
4. Why do water droplets form on the outside of a glass filled with ice water?
5. What is the primary difference in shape between a solid (ice) and a liquid (water)?
6. How does a gas (water vapour) behave in terms of shape and spreading?
7. Define the process of melting. What is required for it to occur?
8. Define the process of freezing. How is it achieved?
9. Explain how increasing the surface area affects the rate of evaporation.
10. Why do wet clothes dry faster on a hot, sunny day?
11. What is humidity, and how does it affect the drying time of clothes?
12. Explain the cooling effect of evaporation using the example of an earthen pot (matka).
13. How does a fan make us feel cooler, especially when we are sweating?
14. What are the key steps involved in making a pot-in-pot cooler?
15. What is the role of condensation in the formation of clouds?
16. Why does water vapour rise into the atmosphere?
17. What role do dust particles play in the formation of clouds?
18. What is precipitation? Name three forms it can take.
19. Briefly describe the water cycle.
20. Why is steam visible while water vapour is generally invisible?
21. What happens to the mass of a covered glass of ice water over time, and why?
22. Name three substances other than water that can exist in solid, liquid, and gaseous states.
23. How does the smell of cooking food reach us from the kitchen?
24. If you wanted to dry your clothes quickly on a rainy day, what could you do?
25. Why is it important to use water wisely?

Part B: Multiple-Choice Questions (20 Questions)

1. The process of a liquid turning into a gas is called: a) Condensation b) Evaporation c) Freezing d) Melting
2. Water droplets on the outside of a cold glass are formed by: a) Water seeping through the glass b) Ice melting and overflowing c) Condensation of water vapour from the air d) Evaporation of water from inside the glass
3. Which state of water has a fixed shape and does not flow? a) Liquid b) Gas c) Solid d) Vapour
4. The amount of water vapour in the air is known as: a) Temperature b) Precipitation c) Humidity d) Condensation
5. Evaporation happens faster when: a) The surface area is small b) The air is very humid c) It is a windy day d) It is a cold day
6. The conversion of a solid into a liquid is known as: a) Freezing b) Condensation c) Evaporation d) Melting
7. Earthen pots keep water cool due to which phenomenon? a) Condensation b) Freezing c) Evaporation d) Melting
8. In the water cycle, what happens immediately after evaporation? a) Precipitation b) Condensation c) Collection d) Freezing
9. Clouds are formed from: a) Smoke and dust b) Pure water vapour c) Tiny water droplets condensed around dust particles d) Light gases rising from the Earth
10. Which of the following is an example of a solid? a) Milk b) Oxygen c) Wood d) Oil
11. The conversion of a liquid to a solid is called: a) Melting b) Freezing c) Evaporation d) Condensation
12. Water in which container would evaporate the slowest? a) A wide plate b) A shallow bowl c) A tall, narrow bottle with a small opening d) A mopped floor
13. What provides the energy for melting and evaporation? a) Cold b) Pressure c) Heat d) Wind
14. Water vapour is _______ than air, which causes it to rise. a) Heavier b) Denser c) Colder d) Lighter
15. On a rainy day, evaporation is slow because: a) The temperature is low b) There is no sunlight c) The humidity is high d) The air is not moving
16. What is the continuous circulation of water between the Earth’s surface and the atmosphere called? a) The rain process b) The humidity cycle c) The water cycle d) The atmospheric cycle
17. Steam is visible because it contains: a) Dust particles b) Tiny droplets of water c) Carbon dioxide d) Smoke
18. Sprinkling water on a roof on a hot day cools it down. This is an example of: a) The cooling effect of condensation b) The cooling effect of evaporation c) The heating effect of water d) The insulating property of water
19. Which of the following is NOT a form of precipitation? a) Rain b) Hail c) Cloud d) Snow
20. Which substance mentioned in the text becomes solid during the winter? a) Milk b) Hand sanitiser c) Coconut oil d) Ghee in the fridge

Part C: Essay Questions (For Teachers)

(Provide a detailed, paragraph-length answer)

1. Describe the complete water cycle in detail, explaining the roles of evaporation, condensation, and precipitation.
2. Compare and contrast the physical properties of water in its three states: solid (ice), liquid (water), and gas (water vapour).
3. Explain the three main factors that can speed up the process of evaporation. For each factor, provide a real-world example.
4. Describe the experiment conducted to prove that water droplets on a cold glass come from the air and not from inside the glass. What were the observations and conclusions?
5. What is the “cooling effect of evaporation”? Explain the scientific principle behind it and describe two different examples where this effect is used or observed.
6. How are clouds formed? Explain the entire process from water vapour rising to the formation of visible clouds in the sky.
7. Imagine it is a hot, sunny, and windy day. Now imagine it is a cool, calm, and rainy day. Explain how the rate of evaporation would differ between these two scenarios and why.
8. Describe how to construct and use a “pot-in-pot cooler.” Explain the scientific principle that allows it to keep fruits and vegetables fresh without electricity.
9. Water is described as essential, yet only a small portion is available for use. Discuss the importance of water conservation based on the information provided in the text.
10. The text uses a narrative with characters (Aavi and Thirav) to explore scientific concepts. Choose one “mystery” they investigate (e.g., disappearing puddles or droplets on a glass) and explain how their discussion and activities lead to a scientific understanding of the phenomenon.

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Answer Keys

Answer Key: Part A (Short-Answer Questions)

1. Ice and water are considered different states because they have different physical properties. Ice is solid, hard, and holds its shape, while water is a liquid that flows and takes the shape of its container. However, they are the same substance because ice melts to become water, and water can be frozen to become ice.
2. Evaporation is the process where a liquid, like water, converts into its vapour state (a gas). Two examples are wet clothes drying on a line and water from a puddle disappearing on a hot day.
3. Condensation is the process where water vapour (gas) turns back into its liquid state. This typically happens when the water vapour comes in contact with a cold surface and cools down.
4. Water droplets form on a cold glass because water vapour present in the surrounding air touches the cold outer surface of the glass. The cold surface cools the vapour, causing it to condense into tiny liquid water droplets.
5. A solid like ice has a fixed shape that it retains regardless of the container it is in. A liquid like water does not have a fixed shape and will take the shape of the container it is poured into.
6. A gas like water vapour has no fixed shape and exhibits the property of spreading out to fill the entire available space. It flows freely and is not confined by a container unless it is sealed.
7. Melting is the process of converting a solid into a liquid. This process requires the supply of heat to the substance, which causes its state to change.
8. Freezing is the process of converting a liquid into a solid. This is achieved by cooling the substance, such as by placing water in a cold environment like a freezer.
9. Increasing the surface area allows more of the liquid to be exposed to the air at once. This increases the rate of evaporation, so water spread out on a plate will evaporate much faster than the same amount in a narrow bottle.
10. Wet clothes dry faster on a hot, sunny day because the heat from the sun provides more energy for the water to evaporate. Higher temperatures increase the speed of the evaporation process.
11. Humidity is the amount of water vapour already present in the air. High humidity slows down evaporation because the air is already saturated, making it harder for more water to turn into vapour. This is why clothes dry slowly on humid or rainy days.
12. An earthen pot has tiny pores through which a small amount of water seeps to the outer surface. This water then evaporates, drawing heat from the pot and the water inside, which results in a cooling effect that keeps the stored water cool.
13. A fan moves air across our skin, which increases the rate of evaporation of our sweat. As the sweat evaporates, it draws heat away from our body, creating a cooling sensation.
14. To make a pot-in-pot cooler, you place a smaller earthen pot inside a larger one. The gap between them is filled with sand, which is then made moist by pouring water on it. A lid or wet cloth is placed on top.
15. Condensation is crucial for cloud formation. As warm, moist air rises and cools, the water vapour in it condenses into tiny liquid water droplets around dust particles, which then cluster together to form a visible cloud.
16. Water vapour is lighter than the surrounding air. Similar to how a balloon filled with a light gas rises, the less dense water vapour rises up into the atmosphere.
17. Dust particles in the atmosphere act as surfaces for water vapour to condense upon. The vapour cools and turns into liquid droplets around these tiny, invisible particles, which is a necessary step for cloud formation.
18. Precipitation is water falling from clouds back to Earth. It can take the form of rain (liquid), snow (solid ice crystals), or hail (solid ice pellets).
19. The water cycle is the continuous movement of water between the Earth’s surface and the atmosphere. It involves water evaporating from the surface, rising as vapour, condensing to form clouds, and falling back to Earth as precipitation.
20. Water vapour itself is an invisible gas. Steam, which we see when water boils, is visible because as the hot, moist air rises and mixes with cooler air, some of the vapour condenses back into a cloud of tiny liquid water droplets, which we can see.
21. The mass of a covered glass of ice water increases over time. This is because water vapour from the air condenses on the cold outer surface of the glass, adding the mass of this new liquid water to the total weight.
22. The text mentions wax, oil, and ghee as examples of other substances that can be observed in different states.
23. The smell of cooking food is composed of gaseous particles that spread out from the kitchen through the air. These particles travel and eventually reach our nostrils, allowing us to smell the food even from a distance.
24. To dry clothes on a rainy day, one could increase air movement by using a fan or increase the temperature by placing them in a warmer room. Both actions would help speed up the rate of evaporation despite the high humidity.
25. It is important to use water wisely because only a very small portion of the water on Earth is freshwater that is suitable for use by humans, plants, and animals. With a rising population, the demand for this limited resource is increasing, leading to shortages.

Answer Key: Part B (Multiple-Choice Questions)

1. b) Evaporation
2. c) Condensation of water vapour from the air
3. c) Solid
4. c) Humidity
5. c) It is a windy day
6. d) Melting
7. c) Evaporation
8. b) Condensation
9. c) Tiny water droplets condensed around dust particles
10. c) Wood
11. b) Freezing
12. c) A tall, narrow bottle with a small opening
13. c) Heat
14. d) Lighter
15. c) The humidity is high
16. c) The water cycle
17. b) Tiny droplets of water
18. b) The cooling effect of evaporation
19. c) Cloud
20. c) Coconut oil

Answer Key: Part C (Essay Questions)

1. The water cycle is the continuous circulation of water between the Earth’s surface and its atmosphere. It begins with evaporation, where heat from the sun causes water in oceans, lakes, and rivers to turn into water vapour and rise into the air. This water vapour, being lighter than air, ascends into the atmosphere. As it goes higher, the air becomes cooler, leading to condensation. During condensation, the water vapour cools and turns back into tiny liquid water droplets, which form around microscopic dust particles. These droplets gather to form clouds. When the droplets in the clouds combine and become too large and heavy to remain suspended in the air, they fall back to Earth as precipitation, which can be rain, snow, or hail. This water is then collected in bodies of water or as groundwater, and the cycle begins again.
2. Water’s three states have distinct physical properties. In its solid state (ice), it has a fixed shape and volume; it is rigid and does not flow. In its liquid state (water), it has a definite volume but no fixed shape; it takes the shape of its container and has the ability to flow and spread on a surface. In its gaseous state (water vapour), it has neither a fixed shape nor a fixed volume; it expands to fill the entire space of its container and spreads freely in the air.
3. Three main factors that speed up evaporation are temperature, surface area, and air movement.
   • Temperature: Higher temperatures provide more energy for water molecules to escape as vapour. A real-world example is wet clothes drying much faster on a hot, sunny day than on a cool, cloudy day.
   • Surface Area: A larger exposed surface area allows more water molecules to be in contact with the air simultaneously. For example, water spilled on a floor as a wide puddle will evaporate faster than the same amount of water in a narrow glass.
   • Air Movement: Wind or moving air carries away the humid air near the water’s surface, replacing it with drier air, which encourages more evaporation. This is why clothes on a line dry quicker on a windy day.
4. The experiment to prove the origin of water droplets on a cold glass involved observing both the water level inside and the total mass of the system. First, the water level inside the glass was marked; it was observed that this level did not decrease, proving water was not seeping out. Second, the glass of ice water was placed on a digital weighing balance. The mass was recorded over 30 minutes and was observed to increase. The conclusion was that the extra mass came from water vapour in the air condensing onto the cold outer surface of the glass, adding water (and thus mass) from the outside.
5. The “cooling effect of evaporation” is the phenomenon where a surface becomes cooler as a liquid evaporates from it. The scientific principle is that the process of evaporation requires energy, which it takes in the form of heat from its surroundings. When the liquid evaporates, it carries this heat away, leaving the original surface cooler. One example is an earthen pot (matka), which stays cool because water seeps through its pores and evaporates from the outside, drawing heat from the water inside. Another example is feeling cold after applying hand sanitiser; the alcohol in the sanitiser evaporates very quickly, drawing heat from the skin and creating a cooling sensation.
6. Clouds are formed through the process of condensation in the atmosphere. It begins when water evaporates from the Earth’s surface, turning into invisible water vapour. Because water vapour is lighter than air, it rises. As the moist air ascends to higher altitudes, it expands and cools. When the air cools to a certain point (the dew point), the water vapour can no longer stay in its gaseous form and condenses back into microscopic liquid water droplets. This condensation process happens on tiny, invisible dust particles suspended in the air. Millions of these tiny droplets then cluster together, becoming visible from the ground as a cloud.
7. The rate of evaporation would be drastically different between the two scenarios. On a hot, sunny, and windy day, evaporation would be very fast. The high temperature provides ample energy, the wind constantly removes humid air from the surface, and the sun provides direct heat, all of which accelerate evaporation. Conversely, on a cool, calm, and rainy day, evaporation would be very slow. The low temperature provides less energy for evaporation, the lack of wind means the air near the surface remains humid, and the rain indicates that the air is already saturated with water vapour (high humidity), making it very difficult for more water to evaporate.
8. A pot-in-pot cooler is constructed by placing a small earthen pot inside a larger one and filling the space between them with sand. Water is then poured onto the sand to make it constantly moist. Fruits and vegetables are placed inside the smaller, dry pot, which is then covered with a lid or a wet cloth. The scientific principle is the cooling effect of evaporation. The water from the moist sand continuously evaporates from the outer surface of the larger pot, drawing heat energy away from the inner pot and its contents. This process acts as a natural, electricity-free refrigerator, keeping the produce cool and fresh for a longer period.
9. The text highlights that although the Earth is covered in water, most of it is saltwater in oceans and cannot be used directly. The amount of freshwater available for drinking, agriculture, and daily use by humans, animals, and plants is very small. The text also states that the demand for this limited resource is increasing as the global population rises. This combination of a finite, small supply and growing demand leads to water shortages in many parts of the world. Therefore, water conservation—using water wisely, avoiding waste, and preventing pollution—is a critical responsibility to ensure this essential resource remains available for everyone.
10. One mystery Aavi and Thirav investigated was the appearance of water droplets on the outer surface of a cold glass of lemonade. Thirav initially hypothesized that the water might have seeped out of the glass. Aavi countered this by noting the water level inside hadn’t decreased. To test this further, they designed an experiment to see if a change in water level would be noticeable in a tall, narrow bottle, and ultimately weighed the glass to see if its mass changed. The observation that the mass increased while the internal water level remained constant led them to the scientific understanding of condensation: the droplets were not coming from inside the glass but were formed from water vapour in the surrounding air cooling and turning to liquid on the cold surface.

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Glossary of Key Terms

Term	Definition
Condensation	The process of conversion of water vapour into its liquid state.
Cooling Effect	The phenomenon where a surface becomes cooler as a liquid evaporates from it, because the process of evaporation removes heat.
Evaporation	The process of conversion of water into its vapour state.
Freezing	The process of conversion of a liquid into a solid state.
Gas	A state of matter with no fixed shape or volume, which spreads out to fill any available space (e.g., water vapour).
Humidity	The amount of water vapour in the air.
Liquid	A state of matter that flows, has a constant volume, and takes the shape of its container (e.g., water).
Melting	The process of conversion of a solid into a liquid state.
Precipitation	Water falling from clouds back to the Earth’s surface, such as rain, hail, or snow.
Solid	A state of matter that retains its shape and does not flow (e.g., ice).
States	The different forms in which a substance can exist, such as solid, liquid, and gas.
Steam	Water vapour that is made visible by the presence of tiny condensed water droplets.
Water Cycle	The continuous circulation of water between the Earth’s surface and the atmosphere, involving evaporation, condensation, and precipitation.
Water Vapour	The gaseous state of water, which is generally invisible.