NCERT Solutions for Class 6 Science Chapter 8 a Journey Through States of Water (PDF) – 2027

Aavi is right — ice and water are the same substance in two different states (solid and liquid).

Thirav noticed that ice is hard and can be held, while water flows away. That is a difference of state, not of substance. Ice melts back into the same water, and water freezes back into ice — nothing is added or removed; only heat is given or taken away.

No, Thirav is not right. Nothing gets added to water in the freezer; the water only loses heat and freezes.

How to find out: take a small plastic bottle, fill it with water (not to the brim), close it tightly and weigh it. Keep it in the freezer until the water becomes ice, then weigh it again — the mass is the same. Let the ice melt: the same clear water comes back. So ice is only water in its solid state.

Observation: the ice cube slowly becomes smaller, and after some time only water is left in the cup.

Conclusion: ice changes into water when kept in a warm room, because it takes heat from its surroundings. This change is called melting. Since the ice turns wholly into water and nothing else is formed, ice and water are two forms (states) of the same substance.

Yes. Ice and water are two forms of the same substance. These forms are called states — ice is the solid state and water is the liquid state.

The two states behave differently: water flows but ice does not; water splashes but ice does not.

Yes. Puddles that are full in the morning become smaller or dry up by the evening.

The water goes away in two ways: some of it seeps into the soil of the playground, and some of it changes into water vapour and mixes with the air (evaporation). So the idea in the speech bubble is only partly right — the soil does absorb some water, but some also goes into the air.

Examples: wet clothes drying on a line, a mopped floor drying, sweat drying under a fan, washed utensils drying, and water sprinkled on a hot tawa vanishing.

Possible reason: the water is not lost. It changes into invisible water vapour and mixes with the air. This is called evaporation.

Only partly. Water cannot seep through the smooth surface of a steel utensil, so the idea that water soaks into the surface does not apply here. The water on the utensils disappears by evaporation — it changes into water vapour and goes into the air.

Activity: put a tablespoon of water on a clean, dry steel plate. Rest the plate on two glasses so that its underside can be seen, with a dry sheet of paper below it. Check the underside and the paper at regular intervals until the water on top has disappeared.

Result: if the underside or the paper gets wet, water is seeping through (Aavi is right). If both stay dry, water is not seeping (Thirav is right). They stay dry — so Thirav is right.

Inference: the water on the plate slowly disappears, but the underside of the plate stays dry all the time. So water does not seep through the steel plate.

Is it enough? Yes, for this question — steel has no pores, and we kept watching the other side. To be surer, we can repeat it a few times. But the activity does not by itself show where the water went.

The water has gone into the air. It changes into its gaseous state, called water vapour, which is invisible — so the water seems to disappear. This change of water into water vapour is called evaporation, and it goes on even at room temperature.

The water takes heat from the hot pan and quickly changes into water vapour, which goes into the air. Part of this vapour cools and turns into tiny water droplets — this is the white steam we see. Water vapour itself is invisible; the tiny droplets in steam make it visible.

Other examples of evaporation: wet clothes drying, a mopped floor drying, sweat drying on our body, wet hair drying after a bath, papads and chillies drying in the sun, and salt being left behind when sea water dries in salt pans.

(iii) Both of these. The playground has soil, so some water seeps into the ground through the spaces between soil particles, and some water evaporates from the surface of the puddle into the air.

The sanitiser evaporates — it changes into vapour and mixes with the air. It disappears quickly because it is mostly alcohol, which evaporates faster than water, and rubbing spreads it into a thin layer with a large exposed area.

Sketch: draw the hot tawa, the water drops on it, the invisible water vapour rising, and the white steam above. Label each part and write a caption under the drawing, as below.

Sample Table 8.1 (write your own observations in the same way):

Possible reasons:

1. Ice came out of the tumbler and melted on the outside.
2. Water seeped out through the wall of the glass.
3. Water splashed out while the ice was being added.
4. Water vapour in the air touched the cold glass and turned into water droplets.

Testing each reason shows that the last one is correct.

The reasons in Fig. 8.4 form a good chain of thinking. The idea that water seeped out is checked by looking at the water level. Since a small fall may not be seen, a tall, narrow bottle makes even a slight change noticeable. The best check is to keep water at room temperature in another tumbler: it stays dry outside, so the glass does not leak — the droplets appear only on the cold tumbler.

Other places: on a bottle of chilled water taken out of the fridge, on the inner side of a cooking-pot lid, and on a bathroom mirror after a hot bath.

Dew in the morning: during the night, leaves and grass cool down and become colder than the air. Water vapour in the air condenses on these cold surfaces as dew drops. It is coldest in the early morning, so we see most dew then; later the Sun warms everything and the drops evaporate.

The drops come from the water vapour rising from the boiling water. When the vapour touches the cooler steel plate, it loses heat and turns back into liquid water (condensation). So the drops collect on the inner side of the plate.

Yes. The ice makes the outer surface of the tumbler very cold. Water vapour in the air touches this cold surface and turns into water droplets. This change of water vapour into its liquid state is called condensation.

Prediction: the mass will increase. The tumbler is cold, so water vapour from the air will condense on its outer surface. This water comes from the air and adds to the mass on the balance.

Yes, the findings match the prediction — the mass increases. Sample readings (your values will differ):

Explanation: water vapour from the air condenses on the cold outer surface of the tumbler. This water was in the air before and is now on the balance, so the reading rises steadily while the tumbler stays cold.

No — we cannot say either of these conclusively from Activity 8.4. The balance weighs the whole set-up together. If some water seeped out through the glass, it would still stay on the balance, so the reading would not show it. The rise in mass proves that water has come from the air (condensation), but it cannot prove that no water is seeping out at the same time.

Modification: repeat Activity 8.4 after marking the water level on the tumbler with a permanent marker or a strip of tape.

Observation: the water level inside does not go down, but more and more water collects on the outer surface.

Conclusion: water is not seeping out of the tumbler; the extra water collects outside because of condensation.

How to do it: note the humidity (%) given in the newspaper or the India Meteorological Department (IMD) weather report every day for a year. Find the average for each month and draw a graph of month against humidity.

Likely pattern: humidity is low in the dry summer months (April–May), highest in the monsoon (June–September), and moderate in winter, when mornings are more humid than afternoons.

No change in shape. The ice cube keeps its own shape in whichever container it is put. It only becomes a little smaller and rounder as it melts, but the container does not change its shape. A solid has a fixed shape.

Unlike ice, water flows easily from one container to the other. It has no fixed shape — it takes the shape of the container it is poured into. But its amount (volume) stays the same.

Observation: the water spreads out over the surface into a thin layer, keeping its volume the same.

Table 8.3 (completed):

Water vapour spreads out into the entire space available — in all directions, even upwards — and fills the whole room or container. Water spreads only over a surface and stays at the bottom of its container, keeping its volume the same. So a gas spreads much more than a liquid.

• Ice (solid): has a fixed shape whatever the container; it does not flow or spread.
• Water (liquid): has no fixed shape — it takes the shape of the container; it flows and spreads, but its volume stays the same.
• Water vapour (gas): has no fixed shape; it spreads out into the entire available space. It is invisible and is present in the air even at room temperature.

Solids: stone, wood, glass, brick, chalk, salt.

Liquids (five more besides milk and oil): honey, kerosene, lemon juice, ink, buttermilk.

Gases: oxygen, carbon dioxide, nitrogen, water vapour, cooking gas (LPG).

Yes. The smell of the cooking food mixes with the air. Like a gas, it spreads out into all the space available — out of the kitchen and into the other rooms — and reaches our nose even when we are not in the kitchen.

We change the state of water by heating or cooling it: heating turns ice into water and water into water vapour; cooling turns water vapour into water and water into ice.

To change ice into water quickly, give it heat faster — keep it in the sun or a warm place, put it in a steel bowl, pour warm water over it, or break it into small pieces.

We must cool the water — take heat away from it — by placing it in a cold place such as the freezer of a refrigerator. The water freezes and becomes ice. (If the ice is taken out, it melts back into water.)

Yes — candle wax changes from solid to liquid. To melt the wax: heat it, for example by lighting the candle. To make liquid wax solid again: cool it.

Other liquids that turn solid: coconut oil and ghee in winter, melted chocolate in a fridge, hot sugar syrup setting into sweets, and water freezing into ice.

A Solid, B Liquid, C Gas; 1 Melts, 2 Evaporates, 3 Freezes, 4 Condenses.

Conditions that affect evaporation: temperature (faster on a hot day), movement of air (faster with a fan or on a windy day), exposed area (faster when a cloth is spread out), and humidity (slower on a rainy day, when the air already has much water vapour).

Hot day vs cold day: water evaporates much faster on a hot day — clothes and sweat dry quickly. On a cold day evaporation is slower, but it does not stop.

• Kept the same: the amount of water (or sanitiser), the place — both kept side by side, so the same temperature, air movement and humidity — and the starting time.
• Changed: only the exposed area of the water — small in the bottle cap, large in the plate.
• Measured: the time taken for the water to evaporate completely in each case.

Table 8.4 (sample readings for one teaspoon of water on a warm day; yours will differ):

Conclusion: the water in the plate evaporates much faster than the same amount in the bottle cap. The larger the exposed area of water, the faster it evaporates.

The same result would be seen: milk in the plate would dry up sooner than milk in the bottle cap, because the water in the milk evaporates and a larger exposed area still makes it faster. But the milk would not disappear completely — a dry, whitish layer of milk solids would be left behind, and it may take a little longer than water.

Sample design — air movement: put equal amounts of water in two identical saucers in the same room. Keep one under a running fan and the other in still air. Change only the air movement; keep the amount of water, the saucers, the place and the starting time the same.

Table 8.5 (sample):

Result: water evaporates faster in moving air.

This is a self-check, so write about your own work.

Sample answer: I measured the same amount of water for the bottle cap and the plate, kept both side by side so that only the exposed area was different, and noted the times carefully in Table 8.4. Next time I will check more often, so that my timing is more exact.

Sample record (equal amounts of water in identical caps; yours will differ):

Conclusion: water evaporates faster from the cap kept in sunlight than from the cap kept in shade — heat makes water evaporate faster. In the same way, clothes dry faster on a hot sunny day and on a windy day, and slowly on a rainy (humid) day.

Faster. On a windy day the moving air carries away the water vapour from near the wet clothes and brings in drier air, so the water evaporates faster. The greater the movement of air, the faster water evaporates.

On a rainy day the air is already humid, so we use the other conditions:

• Wring the clothes well first.
• Spread each garment out fully, with gaps between them (larger exposed area).
• Dry them under a fan or in a breezy place (more movement of air).
• Dry them in a warm room, or iron them (higher temperature).

The earthen pot has tiny pores. Water seeps through them to the outer surface and evaporates. To evaporate, the water takes heat from the pot and the water inside, so the water becomes cool — this is the cooling effect of evaporation. A stainless steel pot has no pores, so no water evaporates from its outer surface and the water does not get cooler.

Examples of the cooling effect: sprinkling water on the floor or roof in summer; sweat drying from our body; feeling cool under a fan when we are sweating; a surahi or matka keeping water cool; a wet cloth on the forehead during fever; a desert cooler.

Our hands feel cool. The sanitiser evaporates quickly, and to evaporate it takes heat from our skin. The skin loses heat and so feels cold — this is the cooling effect of evaporation.

Water poured into the sand keeps the outer pot wet. The water seeps through the pores of the pot to its outer surface and evaporates. Evaporation takes heat from the pots, the sand and the things inside, so the inside of the small pot becomes cooler. The wet jute sack on top cools the opening in the same way. Adding water regularly keeps the cooling going, without electricity.

Sample result: most vegetables and fruits stay fresh for about a week in the cooler (leafy greens for fewer days), compared with only 2–3 days on an open shelf.

Conditions that affect the number of days: how hot and dry the air is, air movement around the cooler, keeping it in shade, adding water regularly to keep the sand moist, the type of pots (unglazed clay works best), and how fresh the vegetables and fruits were.

Anything that holds plenty of water and lets air pass can be used, for example wet jute (gunny) cloth, coir or coco peat, sawdust or khus (vetiver) roots. These hold more water than sand, so they keep the outer pot wet for longer and give better cooling.

Water evaporates from oceans, rivers and land, and the water vapour rises with the air. Higher up, the air becomes cooler and cooler. At a certain height the water vapour condenses into tiny droplets, usually around dust particles. These droplets float and form clouds. Many droplets join to form bigger drops, which become heavy and fall as rain (or sometimes as hail or snow).

Because water vapour is lighter than air, air containing water vapour rises — just as balloons filled with a lighter gas go up in the air.

Sample completion (the two new lines are highlighted):

The space above the water stays clear — no cloud forms (at most a faint mist that vanishes at once). The air in the bottle has water vapour, and releasing the bottle cools the air a little, but there are hardly any dust particles for the vapour to condense on.

Now some haziness (a cloud) appears above the water in the bottle. The burnt newspaper gives very small, invisible dust particles. Water vapour in the bottle condenses around these particles into tiny droplets, which together look like a cloud. This shows that dust particles help clouds to form.

The figure with all nine words placed:

This is a self-check, so write honestly about your own work.

Sample answer: I labelled the ocean, cloud, rain, river and snow correctly, with evaporation on the upward arrows and rain on the downward arrows. Yes, I could label all nine words, but I had to think about groundwater. At first I was unsure where condensation goes — now I know it is where the cloud forms.

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

Condensation is the change of water vapour (gas) into water (liquid). Options (i) and (ii) describe evaporation, and (iii) is a result of condensation, not condensation itself.

(i) (b) water colours and (c) acrylic colours — both are put on wet and dry only when the water in them evaporates. Crayons and pencil colours are dry, so nothing has to evaporate.

(ii) (b) ink pen — the liquid ink dries on the paper by evaporation. A pencil leaves a dry mark, and ball pen ink is a thick paste that hardly needs to dry.

Natural grass contains water, and water keeps evaporating from its leaves and the moist soil below. Evaporation takes heat from the grass and the air around it, so the space feels cooler — the cooling effect. Plastic grass has no water to evaporate, so it just absorbs sunlight, gets hot and warms the air around it.

Liquids other than water that evaporate: spirit (alcohol, as in hand sanitiser), petrol, kerosene, perfume, and nail-polish remover (acetone). Many of these evaporate even faster than water.

A fan does not need to supply heat. The heat needed for evaporation comes from the wet clothes and the surrounding air, which are already at room temperature — evaporation happens at all temperatures. The fan only moves the air: it carries away the moist air near the clothes and brings in drier air, so water evaporates faster and the clothes dry sooner. We feel cool under a fan for the same reason — it makes our sweat evaporate faster.

During the 3–4 days, much of the water in the sludge evaporates in the sun and air.

• Lower transport cost: the dried sludge is much lighter and smaller in volume, so fewer trips and less fuel are needed.
• Safer handling: dry sludge is firm and does not splash or spill, it smells less, and many germs are killed as it dries in the sun — so it is safer for the workers.

Activities involving evaporation: drying clothes and a wet towel, a mopped floor drying, washed utensils drying, drying papads or chillies in the sun, sweat drying under a fan, water staying cool in a matka, and boiling down milk.

How it helps: knowing what makes evaporation faster, we can dry clothes and food quickly (spread out, in sun and breeze), keep water cool in a matka, and cool rooms by sprinkling water.

In nature, water is found in the solid state as ice wherever it is very cold (0 °C or below):

• snow on high mountains such as the Himalayas, and falling snow;
• glaciers and the ice of the polar regions;
• hail (hailstones) that falls during some storms;
• frozen lakes and rivers in very cold places, such as Ladakh.

I agree. Only a small part of the Earth’s water is fit for use, and the demand for it keeps growing. Everyone has a right to clean water, but that right can be met only if each of us first takes the responsibility to save water and keep it clean. So I close the tap while brushing, reuse water for plants, never throw waste into ponds or rivers, and support rainwater harvesting.

Sprinkle a little water on the seat (or wipe it with a wet cloth) and let it dry. As the water evaporates, it takes heat from the seat, so the seat cools — the cooling effect of evaporation. Fanning it or moving the vehicle into a breeze makes the water evaporate faster. Parking in the shade or covering the seat also stops it from getting so hot.

Observation: the wet hand feels much cooler than the dry hand.

Reason: blowing air makes the water on the wet hand evaporate faster. To evaporate, the water takes heat from the skin, so the wet hand feels cold. The dry hand has no water to evaporate, so it does not cool. The cooling comes from evaporation, not from the air being cold.

Sample game — ‘Water’s Journey’ (like snakes and ladders): draw a board of 40 squares from OCEAN (start) to BACK TO THE OCEAN (finish). Ladders are changes that take water up (evaporation, a hot sunny day, wind); snakes bring it down (condensation, rain, snow, freezing). Some squares have a ‘?’ — the player picks a challenge card, such as ‘Name the change gas → liquid’ (condensation), and moves forward for a correct answer.

Sample plan: children play the Sun, water drops, Evaporation, a dust particle, Condensation, the Cloud, Rain/Hail/Snow, the River and Groundwater. The Sun warms the drops, which rise as vapour; they gather round the dust particle to form a cloud; they fall as rain and flow back through the river to the ocean. At the end, all stand in a circle to show that the cycle never ends.