Class 6 Science · Chapter 8

8. A Journey through States of Water

Answers to in-text questions, activities and Let us enhance our learning. NCERT Curiosity, Class 6 Science (CBSE).

Activities and In-text Questions

Thirav thinks ice and water are different substances. Aavi has a counterview. What do you think?

Aavi is right. When an ice cube is left in a cup, it changes into water (Activity 8.1).

Ice and water are two states of the same substance.

8.2Keep a tablespoon of water on a steel plate. Does water seep through the plate? Where does the water go?

No. Water does not seep through the steel plate.

The water slowly changes into water vapour and goes into the air. This process is called evaporation.

What happens to the water we sprinkle on a hot pan while making dosa?

The water quickly changes into steam (water vapour) because the pan is hot. Some of it turns into tiny water droplets which we can see.

What is the reason for disappearance of water from the puddles? Hand sanitiser disappears as you rub it. What happens to it?

Water from puddles disappears due to both seeping into the ground and evaporation.

Hand sanitiser evaporates into the air.

8.3Take cold water with ice cubes in a glass tumbler. What do you observe on the outer surface after five minutes? (Table 8.1)

I observe	I wonder
Tiny water droplets appear on the outer surface.	Where do these droplets come from?
The droplets join to form bigger drops.	Has water seeped out of the tumbler?
The outer surface feels cold and wet.	Will this happen with a metal tumbler too?

Why do we see dew drops more in the morning? Where do the drops on the plate covering boiling water come from?

At night, plants and grass become cool. Water vapour in the air touches these cool surfaces and turns into water droplets. These are dew drops.

Water vapour from the boiling water touches the cooler plate and changes into drops. This is condensation.

8.4Predict what will happen to the mass of the tumbler with cold water kept on a digital balance.

The mass increases slowly. Water vapour from the air condenses on the cold outer surface and adds to the mass.

When we mark the water level, the level does not go down. So water is not seeping out. The extra water outside comes from condensation.

8.5Compare the different states of water (Table 8.3).

Property	Ice (solid)	Water (liquid)	Water vapour (gas)
Shape	Fixed shape	Takes the shape of the container	No fixed shape
Ability to flow	Does not flow	Flows	Flows
Ability to spread	Does not spread	Spreads, volume stays the same	Spreads in the entire space

Give examples of solids, liquids and gases.

Solids: stone, wood, glass, wax, ice.

Liquids: milk, oil, juice, honey, kerosene, petrol, vinegar.

Gases: oxygen, carbon dioxide, nitrogen, water vapour, LPG.

8.6Fill up the blank boxes in Fig. 8.5 for conversion of different states of water.

A. Solid → 1. Melts → B. Liquid → 2. Evaporates → C. Gas

C. Gas → 4. Condenses → B. Liquid → 3. Freezes → A. Solid

8.7Keep the same amount of water in a bottle cap and in a plate. What did we keep the same, what did we change and what did we measure?

Kept the same: amount of water and the place.

Changed: exposed area of water.

Measured: time taken for the water to evaporate completely.

Conclusion: Water in the plate evaporates faster. Larger exposed area means faster evaporation. Milk would also evaporate faster from the plate.

8.8What conclusions can you draw from keeping one cap in sunlight and the other in shade?

Water evaporates faster in sunlight than in shade.
Water evaporates faster on a windy day.
Water evaporates slowly on a rainy day because the air is already humid.

If you want to dry your clothes on a rainy day, how can you make it faster?

Spread the clothes out well and dry them under a running fan. This increases the exposed area and the movement of air.

Why is the water in an earthen pot cold? What are other examples of the cooling effect?

Water seeps through the tiny pores of the earthen pot and evaporates. Evaporation causes a cooling effect.

Other examples: sweat drying under a fan, sprinkling water on the floor or roof in summer, the cool feeling when sanitiser is rubbed on hands.

8.10What do you observe when a burnt piece of paper is put in the bottle and the bottle is squeezed?

Haziness (a cloud) appears above the water. Tiny dust particles from the burnt paper help water vapour to condense around them and form a cloud.

8.11Label Fig. 8.9 to show how water changes its state and moves.

Water from the ocean, rivers and lakes changes into water vapour by evaporation.

Water vapour rises, cools and forms clouds by condensation.

Water falls back as rain or snow.

Some water seeps in to become groundwater. Rivers carry the rest back to the ocean.

This circulation of water is called the water cycle.

Let us enhance our learning

1Which of the following best describes condensation?

(iv) The conversion of water vapour into its liquid state.

2Identify in which of the given processes evaporation is very important.

(i) Colouring with (b) water colours

(ii) Writing on paper with (b) ink pen

Water colours and ink are wet. They dry only when the water in them evaporates.

3Space around natural grass feels cooler than space around plastic grass. Why?

Natural grass and the soil below it contain water. This water keeps evaporating and causes a cooling effect.

Plastic grass has no water to evaporate. It gets hot in the Sun.

4Give examples of liquids other than water that evaporate.

Petrol, kerosene, spirit (alcohol), hand sanitiser, perfume and nail polish remover.

5It might seem strange to use a fan to dry wet clothes since fans make things cooler. What do you think about this?

A fan increases the movement of air. Moving air carries away the water vapour near the clothes. So more water evaporates quickly.

The heat needed for evaporation comes from the surroundings. So clothes dry faster under a fan.

6Sludge removed from drains is left in heaps for 3–4 days before it is transported. Explain how this reduces transport cost and improves safety.

In 3–4 days, most of the water in the sludge evaporates. The sludge becomes dry and lighter.

Dry sludge is lighter, so transport costs less. It does not spill or splash, so it is safer to handle.

7Identify the activities in your house that involve evaporation. How does understanding evaporation help us?

Drying washed clothes
Drying of a mopped floor
Drying washed utensils
Drying papad, chillies and pickles in the Sun
Cooling of water in an earthen pot

Knowing about evaporation helps us dry things faster. We spread them out, keep them in the Sun or under a fan.

8How is water present in the solid state in nature?

As ice and snow on high mountains, glaciers and polar regions. Also as hail and frozen lakes in very cold places.

9Reflect on the statement “Water is our responsibility before it is our right.” Share your thoughts.

Only a small part of water on Earth is fit for use. All living beings need it.

So before we demand water as our right, we must save it. We should not waste or pollute it. Only then will there be enough water for everyone.

10The seat of a two-wheeler parked on a sunny day has become very hot. How can you cool it down?

Sprinkle some water on the seat or wipe it with a wet cloth. As the water evaporates, it takes heat from the seat and cools it.

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