A Journey through States of Water — Class 6 Science
Curiosity · Chapter 8
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5- Mathematics
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- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
Chapter summary
Key ideas & terms
- States of water
- The three forms of water — ice (solid), water (liquid), and water vapour (gas) — which are all the same substance in different states.
- Evaporation
- The process of conversion of water into its vapour state, which takes place continuously even at room temperature.
- Condensation
- The process of conversion of water vapour into its liquid state, as when vapour in the air meets a cold surface.
- Melting and freezing
- Melting is the conversion of a solid into a liquid; freezing is the conversion of a liquid into a solid.
- Cooling effect of evaporation
- The cooling produced when water evaporates, as in earthen pots and surahis that keep water cool.
- Water cycle
- The circulation of water between the Earth's surface and the atmosphere through evaporation, condensation, and rain, hail, or snow.
Extra questions & answers
Are ice and water the same substance?
Yes; ice and water are two states, or forms, of the same substance, differing only in behaviour — water flows and splashes while ice does not.
What is evaporation?
Evaporation is the process of conversion of water into its vapour state; it takes place continuously even at room temperature, as when wet clothes or mopped floors dry.
What is condensation?
Condensation is the process of conversion of water vapour into its liquid state, as when vapour in the air meets a cold surface and forms water droplets.
Why do water droplets form on the outside of a glass of cold water?
Because water vapour present in the air comes in contact with the cold surface of the glass and condenses into tiny droplets of liquid water.
How do the shapes of ice, water, and water vapour differ?
Ice keeps a fixed shape and does not flow or spread; water flows and takes the shape of its container with a fixed volume; water vapour spreads to fill all available space.
What is the difference between melting and freezing?
Melting is the conversion of a solid into a liquid, such as ice into water, while freezing is the conversion of a liquid into a solid, such as water into ice.
What conditions make water evaporate faster?
A larger exposed surface area, the presence of sunlight or warmth, and increased movement of air all make water evaporate faster, while high humidity makes it slower.
Why does water stay cool in an earthen pot or surahi?
Water seeps through the surface of the earthen pot and evaporates, and this evaporation produces a cooling effect that keeps the remaining water cool.
How do clouds form and give rain?
As air rises and cools, water vapour condenses around dust particles into tiny droplets that form clouds; many droplets join into drops heavy enough to fall as rain, hail, or snow.
What is the water cycle?
The water cycle is the circulation of water between the Earth's surface and the atmosphere, as water evaporates, condenses, and returns as rain, hail, or snow.
Let us enhance our learning
1. Which of the following best describes condensation? (i) The conversion of water into its vapour state. (ii) The process of water changing from a liquid into gaseous state. (iii) The formation of clouds from tiny water droplets. (iv) The conversion of water vapour into its liquid state.
The correct option is (iv) The conversion of water vapour into its liquid state. Condensation is the opposite of evaporation. When water vapour present in the air touches a cold surface it cools and changes back into tiny droplets of liquid water. Option (i) and (ii) describe evaporation, and (iii) is a result of condensation in the sky, not its definition.
2. Identify in which of the given processes, evaporation is very important— (i) Colouring with (a) crayons (b) water colours (c) acrylic colours (d) pencil colours
Evaporation is very important when colouring with (b) water colours. Water colours are made by mixing pigments in water. After painting, the water evaporates and leaves the colour on the paper. Crayons, acrylic colours and pencil colours do not use water as a main solvent in the same way, so evaporation is not important for them.
2. Identify in which of the given processes, evaporation is very important— (ii) Writing on paper with (a) pencil (b) ink pen (c) ball point pen
Evaporation is very important when writing with (b) ink pen. Ink pen contains liquid ink made with water or other volatile solvents. After writing, the solvent evaporates and the dye remains on the paper. Writing with a pencil uses solid graphite and with a ball point pen uses a thick paste that does not depend mainly on evaporation to dry.
3. We see green coloured plastic grass at many places these days. Space around natural grass feels cooler than space around the plastic grass. Can you find out why?
Natural grass contains water. Water continuously evaporates from the leaves and from the soil around the grass through transpiration. Evaporation needs heat, which is taken from the surrounding air, so the air gets cooler. Plastic grass has no water, so no evaporation and no cooling effect occurs. Hence the area around natural grass feels cooler.
4. Give examples of liquids other than water that evaporate.
Many liquids other than water evaporate, often even faster than water. Examples are hand sanitiser containing alcohol, petrol, kerosene, acetone or nail-paint remover, perfume, spirit and phenyl. Like water, they change into vapour on standing in air.
5. Fans move air around, creating a cooling sensation. It might seem strange to use a fan to dry wet clothes since fans usually make things cooler, not warmer. Normally, when water evaporates, it requires heat, not cold air. What do you think about this?
A fan does not dry clothes by heating them. It helps evaporation in two ways. Moving air carries away the water vapour that has just formed near the wet clothes, so more water can evaporate easily. Fast-moving air also provides a little energy and increases the rate of evaporation. The cooling we feel from a fan is because evaporation of sweat from our skin takes heat from our body. For clothes, the continuous removal of humid air is more important than temperature for fast drying, so a fan is useful even though it makes us feel cool.
6. 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 manure. This approach reduces transportation cost of the sludge and enhances the safety of individuals handling it. Reflect upon it and explain how.
Sludge from drains contains a lot of water. When left in heaps in the sun and open air for 3-4 days, water evaporates and the sludge becomes dry and lighter. Lighter sludge costs less to transport because its weight and volume are reduced. It is also safer because wet sludge contains more harmful germs and smells badly and is slippery and difficult to handle, while dried sludge has fewer germs, less foul smell and is easier to pack and carry. Evaporation of water makes it more suitable to be used as manure.
7. Observe the activities in your house for a day. Identify the activities that involve evaporation. How does understanding the process of evaporation help us in our daily activities?
Activities at home that involve evaporation are drying wet clothes on a clothesline, mopping the floor and seeing it become dry, drying utensils after washing, evaporation of sweat from the body, using a cooler or earthen pot to keep water cold, and boiling water where steam forms. Understanding evaporation helps us to dry clothes faster by spreading them in sunlight and wind and increasing exposed area, to keep drinking water cool in an earthen pot, to cool the house by sprinkling water, to store food properly, and to save water by knowing how the water cycle works.
8. How is water present in the solid state in nature?
In nature water is present in the solid state as ice and snow. It is found as snow on high mountain peaks like the Himalayas, as ice caps and glaciers at the poles, as hailstones during some rains, and as frost and icicles in very cold regions. These are all frozen forms of water.
9. Reflect on the statement “Water is our responsibility before it is our right.” Share your thoughts.
This statement means we must take care of water before we demand it. Only a very small part of Earth's water is fresh and usable. If we waste or pollute it, there will not be enough for everyone in the future. Therefore we should use water wisely, avoid wasting it, keep water bodies clean, conserve rainwater and share it fairly. Protecting water today is our duty so that we and future generations can enjoy the right to clean water.
10. The seat of a two-wheeler parked on a sunny day has become very hot. How can you cool it down?
We can cool the hot seat by sprinkling or wiping it with water. The water will evaporate by taking heat from the hot seat, so the seat becomes cooler. Covering the seat with a wet cloth, parking in shade, or pouring a small amount of water and letting it evaporate are simple ways to use the cooling effect of evaporation. We should then wipe it dry before sitting.
Learning further
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.
When air is blown, water on the wet hand evaporates quickly. Evaporation needs heat, which is taken from the skin of the wet hand, so that hand feels much cooler than the dry hand where there is no evaporation. Moving air removes water vapour faster, increasing the cooling effect.
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.
A simple board game can be made with squares marked Start, Ice, Water, Water Vapour, Cloud, Rain, Ocean and Finish. Players roll a dice and move. On some squares they pick a challenge card such as What is melting? or Name one factor that speeds up evaporation. Correct answer allows them to move ahead, wrong answer makes them miss a turn. This helps to learn melting, freezing, evaporation, condensation and the water cycle while playing.
Discuss with your teacher and act out the stages of the water cycle through a role-playing activity in your school assembly.
Students can form groups to act as the Sun, ocean, water vapour, clouds, wind and rain. One group acts as the Sun heating the ocean, another as water evaporating and rising up as vapour, a group joining hands to become a cloud after condensation around dust particles, and another falling as rain to return to the ocean and rivers. Dialogues can explain evaporation, condensation, cloud formation and precipitation, showing that water circulates continuously between the Earth and the atmosphere.