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A Journey through States of Water

NCERT Class 6 · Science Based on NCERT Class 6 Science textbook · Free CBSE study kit

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Chapter Notes

Overview
This chapter explores the three states of water—solid (ice), liquid (water), and gas (water vapour)—and how water changes from one state to another through processes like melting, freezing, evaporation, and condensation. It is included in the syllabus to help students understand the water cycle and the everyday phenomena around them, such as drying of clothes, formation of dew, and cooling by earthen pots. The one big idea a student must walk away with is that water is the same substance in different forms, and its state changes with heating or cooling, driving the continuous circulation of water on Earth.
Key Concepts (13)
States of water
Water exists in three different states: solid (ice), liquid (water), and gas (water vapour).
e.g. Ice cubes in lemonade are solid, the lemonade itself is liquid, and the steam from a hot pan is gas.
Evaporation
The process of conversion of water into its vapour state.
e.g. Water puddles disappearing on a sunny day; drying of wet clothes.
Condensation
The process of conversion of water vapour into its liquid state.
e.g. Water droplets appearing on the outer surface of a glass tumbler containing ice-cold water; dew drops on plants in the morning.
Melting
The process of conversion of a solid into liquid state.
e.g. Ice cube left in a cup at room temperature turns into water.
Freezing
The process of conversion of liquid into solid state.
e.g. Water placed in a freezer turns into ice.
Water vapour
The gaseous state of water, which is invisible and present in the air around us.
e.g. The steam from boiling water is water vapour; the invisible gas that makes the air humid.
Humidity
The amount of water vapour present in the air.
e.g. On a rainy day, humidity is high; on a dry summer day, humidity is low.
Water cycle
The circulation of water between the Earth's surface and the atmosphere, involving evaporation, condensation, and precipitation.
e.g. Water from oceans evaporates, forms clouds, and returns as rain, which flows back to the oceans.
Cloud
Tiny water droplets formed when water vapour in the air condenses around dust particles, floating in the air.
e.g. White fluffy clouds in the sky are made of tiny water droplets.
Cooling effect of evaporation
When water evaporates, it absorbs heat from the surroundings, causing a cooling sensation.
e.g. Water in an earthen pot (matka) feels cold because water seeps through and evaporates; rubbing sanitiser on hands feels cool.
Solid state
A state of matter that has a fixed shape and does not flow or spread.
e.g. Ice cube retains its shape even when transferred to a different container.
Liquid state
A state of matter that flows, takes the shape of its container, and can spread while keeping volume constant.
e.g. Water poured from a glass into a bowl takes the shape of the bowl.
Gaseous state
A state of matter that has no fixed shape and spreads out to fill all available space.
e.g. Water vapour spreads throughout the room; smell of cooking food reaches us through air.
How It Works
Melting of ice
  1. Ice (solid) is taken out of the freezer and kept at room temperature.
  2. Heat from the surroundings is absorbed by the ice.
  3. Ice changes into water (liquid).
💡 Melting requires heat; it is not the same as dissolving.
Freezing of water
  1. Water (liquid) is placed in a cold environment, such as a freezer.
  2. Heat is removed from the water.
  3. Water changes into ice (solid).
💡 Freezing is the opposite of melting; it occurs when temperature drops below 0°C.
Evaporation of water
  1. Water is exposed to air at any temperature (even room temperature).
  2. Water molecules gain enough energy to escape into the air as invisible water vapour.
  3. The water disappears from the surface.
💡 Evaporation happens continuously, even at room temperature, not only when water boils.
Condensation of water vapour
  1. Water vapour in the air comes in contact with a cold surface.
  2. The vapour loses heat and changes into liquid water droplets.
  3. Droplets appear on the cold surface.
💡 Condensation requires a cold surface; the water droplets come from the air, not from inside the container.
Formation of clouds and rain
  1. Water from oceans, lakes, and rivers evaporates into the atmosphere.
  2. Water vapour rises because it is lighter than air.
  3. As the air rises higher, it becomes cooler.
  4. At certain heights, the cool air causes water vapour to condense around dust particles, forming tiny water droplets.
  5. These tiny droplets float in the air and form clouds.
  6. Many droplets join together to form bigger drops.
  7. When drops become heavy, they fall as rain.
💡 Dust particles are essential for cloud formation; without them, condensation is much slower.
Cooling by evaporation (earthen pot)
  1. Water seeps through the porous surface of the earthen pot (matka).
  2. This water evaporates from the outer surface of the pot.
  3. Evaporation absorbs heat from the pot and the water inside.
  4. The water inside the pot becomes cool.
💡 The cooling effect is due to evaporation, not because the pot itself is cold.
Factors affecting evaporation rate
  1. Exposed area: Larger surface area (e.g., water in a plate) evaporates faster than smaller area (e.g., water in a bottle cap).
  2. Temperature: Higher temperature (sunlight) increases evaporation rate; lower temperature (shade) decreases it.
  3. Air movement: Windy conditions increase evaporation; still air decreases it.
  4. Humidity: High humidity (rainy day) slows evaporation; low humidity (dry day) speeds it up.
💡 All these factors work together; changing one factor can speed up or slow down drying.
Exam Traps — Don't Make These Mistakes
⚠ Confusing evaporation with boiling
✗ Evaporation only happens when water is heated to 100°C.
→ Evaporation occurs at all temperatures, even at room temperature, as seen in drying of wet clothes or puddles disappearing.
✓ Evaporation is the conversion of water into water vapour at any temperature, not just at boiling point.
⚠ Thinking water droplets on a cold glass come from inside
✗ The water droplets on the outside of the glass come from the ice or water inside the glass seeping through.
→ The water level inside the glass does not decrease, and the glass is non-porous, so water cannot seep through. The droplets come from water vapour in the air condensing on the cold surface.
✓ The water droplets form because water vapour in the air condenses on the cold outer surface of the glass.
⚠ Mixing up melting and freezing
✗ Melting is when water turns into ice.
→ Melting is the change from solid to liquid (ice to water). Freezing is the change from liquid to solid (water to ice).
✓ Melting is the conversion of a solid into a liquid (e.g., ice to water). Freezing is the conversion of a liquid into a solid (e.g., water to ice).
⚠ Believing steam is water vapour
✗ Steam is water vapour.
→ Steam is actually a mixture of water vapour (invisible) and tiny visible water droplets. Pure water vapour is invisible.
✓ Steam contains water vapour and tiny water droplets; water vapour itself is invisible.
⚠ Thinking evaporation only happens on hot days
✗ Water evaporates only when it is sunny or hot.
→ Evaporation happens continuously at all temperatures, even on cold days, though it is slower.
✓ Evaporation occurs at all temperatures, but it is faster on hot, windy, or dry days.
Compare & Contrast
Direction of state change
Evaporation
Condensation
Evaporation is the change from liquid water to water vapour (gas); condensation is the change from water vapour (gas) to liquid water.
Direction of state change
Melting
Freezing
Melting is the change from solid (ice) to liquid (water); freezing is the change from liquid (water) to solid (ice).
Shape and flow
Solid state (ice)
Liquid state (water)
Ice has a fixed shape and does not flow; water takes the shape of its container and flows.
Spreading behaviour
Liquid state (water)
Gaseous state (water vapour)
Water spreads but keeps its volume constant; water vapour spreads out to fill the entire available space.
Exam Focus
Marks pattern: 2 MCQs (1 mark each), 1 Very Short Answer (1 mark), 1 Short Answer (3 marks), 1 Long Answer (5 marks) — total 10-12 marks
Most asked: Evaporation and condensation definitions and examples · Water cycle diagram and explanation · Factors affecting evaporation rate · Cooling effect of evaporation (earthen pot, sanitiser) · Differences between states of water (solid, liquid, gas)
Don't skip: Explain the water cycle with a labelled diagram (5 marks); Describe an activity to show condensation (3 marks); Why does water in an earthen pot become cool? (3 marks); List three factors that affect evaporation and give examples (3 marks)
One-Line Revision (read aloud before the exam)
  1. Water exists in three states: solid (ice), liquid (water), and gas (water vapour).
  2. Evaporation is the change of water into water vapour at any temperature.
  3. Condensation is the change of water vapour into liquid water on a cold surface.
  4. Melting is the change of solid ice into liquid water on heating.
  5. Freezing is the change of liquid water into solid ice on cooling.
  6. Water vapour is invisible; steam contains tiny visible water droplets.
  7. Evaporation causes a cooling effect because it absorbs heat from the surroundings.
  8. Water in an earthen pot (matka) becomes cool due to evaporation of water seeping through the pot.
  9. Factors that speed up evaporation: larger exposed area, higher temperature, wind, and low humidity.
  10. Clouds form when water vapour condenses around dust particles in the cool upper air.
  11. Rain falls when cloud droplets join together and become heavy.
  12. The water cycle is the continuous circulation of water between the Earth's surface and the atmosphere.
  13. Humidity is the amount of water vapour in the air; high humidity slows evaporation.
  14. Ice has a fixed shape and does not flow; water takes the shape of its container and flows.
  15. Water vapour spreads out to fill all available space, unlike liquid water which has a fixed volume.
  16. Dew drops on plants in the morning are formed by condensation of water vapour from the air.

MCQs — 10 Questions with Answers

Q1. What happens to an ice cube when left on a table at room temperature?

  • A. It melts and becomes water ✓
  • B. It remains as ice forever
  • C. It turns into salt
  • D. It breaks into smaller pieces

Answer: A — Heat from room temperature causes ice to melt and convert into liquid water.

Q2. Which of the following is an example of evaporation?

  • A. Ice melting in the refrigerator
  • B. Water droplets forming on a cold glass
  • C. Wet clothes drying on a rope ✓
  • D. Water freezing in the freezer

Answer: C — Evaporation is when water converts into water vapour and disappears; wet clothes drying is a clear example.

Q3. The process of conversion of water vapour into liquid water is called _________.

  • A. Evaporation
  • B. Melting
  • C. Condensation ✓
  • D. Freezing

Answer: C — Condensation is when water vapour (gas) converts into liquid water droplets on cold surfaces.

Q4. Why do water droplets appear on the outside of a cold glass tumbler containing ice water?

  • A. Water seeps through the glass
  • B. Ice melts and spills over
  • C. Water vapour in air condenses on the cold glass surface ✓
  • D. Glass attracts moisture from inside

Answer: C — The cold glass surface causes water vapour in the surrounding air to condense into visible water droplets.

Q5. Which of the following statements is true?

  • A. Ice and water are different substances
  • B. Ice and water are the same substance in different states ✓
  • C. Water cannot change into ice
  • D. Ice is heavier than water

Answer: B — Ice and water are the same substance (H₂O) but in different physical states — ice is solid, water is liquid.

Q6. Dew drops on grass in the early morning are formed due to _________.

  • A. Evaporation
  • B. Rain
  • C. Condensation of water vapour ✓
  • D. Melting of frost

Answer: C — At night, water vapour in the cool air condenses on cold grass leaves forming dew drops.

Q7. What is the main difference between steam and water vapour?

  • A. Steam is colder than water vapour
  • B. Water vapour is invisible while steam appears visible ✓
  • C. Steam is only produced from boiling water
  • D. Water vapour is only formed in hot areas

Answer: B — Water vapour is pure invisible gas, while steam is water vapour mixed with tiny visible water droplets.

Q8. If you sprinkle water on a hot dosa pan, the water quickly disappears. This process is called _________.

  • A. Melting
  • B. Freezing
  • C. Evaporation ✓
  • D. Condensation

Answer: C — The heat from the hot pan causes water to rapidly evaporate and convert into invisible water vapour.

Q9. Water puddles disappear from the playground after rain mainly because of _________.

  • A. Only seeping into the ground
  • B. Only evaporation
  • C. Both evaporation and seeping into the ground ✓
  • D. Water being absorbed by air

Answer: C — Puddle water both evaporates into the air as water vapour and seeps into the soil below.

Q10. When water boils in a covered pot and water droplets appear on the inner side of the lid, this demonstrates _________.

  • A. Evaporation only
  • B. Melting process
  • C. Both evaporation and condensation ✓
  • D. Freezing process

Answer: C — Water evaporates from the boiling liquid, and the water vapour condenses back into droplets on the cold lid surface.

Flashcards

What happens to ice when left at room temperature?

Ice melts and converts into water.

Define evaporation.

Evaporation is the process where water converts into its invisible gaseous state called water vapour.

Why do wet clothes dry when hung on a rope?

Water in wet clothes evaporates and becomes invisible water vapour in the air.

What is water vapour?

Water vapour is the invisible gaseous state of water formed when liquid water evaporates.

Define condensation.

Condensation is the process where water vapour in air converts into liquid water droplets when it touches a cold surface.

Why do water droplets appear on the outside of a cold glass tumbler with ice?

Water vapour in the air condenses into liquid water droplets when it comes in contact with the cold glass surface.

Give one example of evaporation from daily life.

Water disappearing from puddles after rain, or sweat drying from our skin, or mopped floor drying.

What is the difference between steam and water vapour?

Steam is visible because it contains tiny water droplets, while water vapour is invisible pure gas.

Does evaporation happen only on hot days?

No, evaporation happens continuously even at room temperature, though it happens faster on hot days.

Where do dew drops come from on plants in the morning?

Water vapour in the cool night air condenses on the cold plant leaves forming dew drops.

Important Board Questions

What are the three states of water? [1 mark]

Name the three physical forms of water: one solid (freezing temperature), one liquid (room temperature), one gas (high temperature). Example from puddle activity.

Explain the difference between evaporation and condensation with one example each from your daily life. [2 marks]

Evaporation = liquid to gas (example: drying of wet clothes). Condensation = gas to liquid (example: water droplets on cold glass). Use the words 'water' and 'water vapour' in your answer.

Why do we see water droplets on the outside of a glass tumbler containing cold water and ice cubes? Explain the process with a reason. [3 marks]

The process is condensation. Water vapour from the air comes in contact with the cold glass surface and converts into liquid water droplets. Connect this to the concept that water vapour is always present in air but is invisible until it condenses.

Describe Activity 8.2 (steel plate with water) and explain what conclusion you draw from it. Draw and label a diagram showing the disappearance of water from the steel plate. [5 marks]

Activity: place water on steel plate, observe, water disappears. Conclusion: water does NOT seep through the steel plate; instead it evaporates and becomes water vapour (invisible gas). Diagram: Show steel plate with water at Day 1, partially disappeared at Day 2, completely gone at Day 3, with arrow showing 'evaporation' or 'water vapour rising into air'.

True or False: Ice and water are different substances. Give one reason to support your answer. [2 marks]

False. Ice and water are the same substance (water/H₂O) in different states. When ice is heated, it melts into water. This proves they are the same substance, just in different physical forms (solid and liquid).

Assertion-Reason Questions for A Journey through States of Water

Q1. Assertion (A):

Ice and water are two different substances.

Reason (R):

When ice melts, it forms water, which shows they are the same substance in different states.

Answer: D — A is false but R is true — The assertion is false. Ice and water are the same substance (H₂O) in different states. The reason is correct—when ice melts it becomes water, proving they are the same substance, not different ones.

Q2. Assertion (A):

Evaporation is the process by which water turns into water vapour.

Reason (R):

Evaporation happens only when water is heated to boiling point.

Answer: C — A is true but R is false — The assertion is true—evaporation is when water turns to vapour. However, the reason is false because evaporation happens even at room temperature (like wet clothes drying or puddles disappearing).

Q3. Assertion (A):

Water droplets appear on the outer surface of a cold glass tumbler because water seeps through the glass.

Reason (R):

Condensation of water vapour from the air on the cold surface explains the appearance of these droplets.

Answer: D — A is false but R is true — The assertion is false because water cannot seep through glass. The reason is true—the droplets form due to condensation, but since the assertion is false, the overall answer is D.

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Case-Based Questions (CBQ) for A Journey through States of Water

Case Study:

Meera's mother prepared chai (tea) in a kettle on the stove. After a few minutes, steam started coming out of the kettle's spout. Meera noticed that when this steam came near a cold mirror hanging on the wall, water droplets appeared on the mirror's surface. She wondered why this happened.

Q1. What is the steam coming out of the kettle spout?

  • A. Frozen water
  • B. Water vapour with tiny visible water droplets ✓
  • C. Pure air with no water content
  • D. Ice particles

Answer: B

Q2. Why did water droplets form on the cold mirror when steam touched it?

  • A. The mirror absorbed the steam
  • B. The steam froze on the mirror
  • C. Water vapour condensed into liquid water on the cold surface ✓
  • D. The steam turned into ice

Answer: C

Q3. What process happens inside the kettle that produces steam?

  • A. Freezing of water
  • B. Condensation of water
  • C. Evaporation of water into water vapour ✓
  • D. Melting of ice

Answer: C

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