A Journey through States of Water

Ice and liquid water are the same substance in different states. In Activity 8.1, an ice cube left in a cup melts as it receives heat from its surroundings. A freezer does not add a new substance to make ice; cooling liquid water sufficiently changes it into a solid.

Water can also be a gas: water vapour. The gaseous state is invisible. The white plume sometimes seen near a kettle or hot pan consists of tiny liquid droplets formed when vapour cools; it is not visible gaseous water.

A puddle can lose water both by soaking into the ground and by evaporation. Evaporation changes liquid water at its surface into water vapour that mixes with the surrounding air. The water has changed state, not ceased to exist.

Activity 8.2 separates these possibilities: place a little water on an intact steel plate, check that its underside stays dry, and observe it over time. Water cannot soak through the steel as it can through soil. Loss from the plate without spilling supports evaporation. Record what actually happens rather than assigning a made-up drying time.

Evaporation occurs at ordinary temperatures; boiling is not required. Wet clothes, a mopped floor and perspiration can dry without reaching 100°C. A hot pan speeds the change, but sunlight and heating to boiling are not conditions that every instance of evaporation needs.

In Activity 8.3, dry the outside of a glass, add cold water and ice, and look again after about five minutes. Note the location of any droplets separately from your proposed explanation, using the “I observe / I wonder” distinction in Table 8.1.

Air contains water vapour. When air next to the cold surface cools sufficiently, some vapour changes to liquid droplets on that surface. This change is condensation. The outside droplets need not have leaked through the glass or come directly from the melting ice inside.

Compare identical intact, covered containers in the same place, one cold and one at room temperature. Start with dry outer surfaces and avoid spills. Greater condensation on the cold surface supports the role of cooling. Visible droplets are not guaranteed in five minutes: humidity and surface temperature matter.

Dew on cool leaves and droplets underneath a lid over warm water are related observations. Humidity describes the water vapour in air. An atmospheric water generator can collect water by condensation, but condensation alone does not establish that collected water is safe to drink.

Activity 8.4 uses a balance to investigate condensation. The balance reads the entire assembly placed on it—not just the water inside. An unchanged water-level mark alone is not proof: small changes may be hard to see, and melting ice and temperature changes complicate the level.

Tables 8.1 and 8.2 are records to complete from observation, not supplied results. Do not invent masses. Repeated trials and a room-temperature control help distinguish condensation from spills, handling and measurement limitations.

1. 1

   Prepare the assembly

   Half-fill a glass with water, add ice and cover it with a steel plate. Dry the outer surfaces. Keep the glass and its cover together on the balance, without adding or removing anything during the trial.

2. 2

   Record at regular intervals

   Record the starting reading and readings every five minutes up to 30 minutes, as in Table 8.2. Use the same units and note visible outside droplets as well as the readings.

3. 3

   State what the reading includes

   Outside condensate remaining on the weighed glass or lid can increase the assembly’s mass. Ice melting inside does not add mass to that assembly. Droplets falling off, evaporation or spills can affect the result.

4. 4

   Check competing explanations

   Combine the mass record, dry-start observation and comparison glass. A sensitive water-level observation is supporting evidence, not a stand-alone demonstration that no water escaped. Report uncertainty if the difference is too small to resolve.

Activity 8.5 compares shape and flow. For a fixed sample under the same conditions, changing a container changes the shape of a liquid, not its volume. Gases spread through the space available to them. Water vapour can be present in ordinary room air.

The categories extend beyond water: stone, wood and glass are solids; milk and oil are liquids; oxygen and carbon dioxide are gases. Food smells spreading across a room show that other substances can travel through air too; smell is not a test for water vapour.

Activity 8.6 asks you to connect the three states. Read both the starting and finishing state before naming the change. Heating and cooling transfer energy; the water remains the same substance through these physical changes.

Melting candle wax and coconut oil becoming more solid in cool weather offer other examples. Different substances change state under different conditions; do not transfer water’s reference temperatures to every material.

A fair comparison changes one factor while keeping the others as similar as possible. In Activity 8.7, put equal small amounts of water in a bottle cap and a plate in the same place: their exposed surface areas differ. Record time and remaining water rather than merely which vessel looks wetter.

Activity 8.8 compares equal amounts in identical caps in sunlight and shade, checking after about 15 minutes. Note temperature, airflow and humidity; a sunlight–shade comparison can change several conditions at once. Repeat on other days rather than claiming the same drying time in all weather.

Use Tables 8.4 and 8.5 to state what changed, what stayed similar and what was observed. Water is sufficient for these comparisons. Milk can lose water by evaporation but leave dissolved or suspended material behind; the whole sample need not vanish.

Evaporation requires energy, which can come from the liquid and its surroundings. In a porous earthen matka or surahi, some water reaches the outer surface through small pores and evaporates. This can cool the water inside. A non-porous steel vessel does not provide the same route.

Perspiration evaporating from skin helps remove heat. A fan can promote that evaporation by moving humid air away; it need not heat the skin to make it dry. A wet hand blown on may feel cooler than a dry one. Alcohol-containing sanitiser can also feel cool as volatile liquid evaporates.

Activity 8.9 makes a pot-in-pot cooler: put sand under and around a smaller earthen pot inside a larger one, wet the sand, and cover the inner space with a lid or damp jute. Keep the sand moist and compare temperatures after several hours. The book suggests observing vegetables over a week; record actual conditions rather than promising a fixed storage life.

The effect depends on humidity, airflow and the materials. A pot cooler is not a guaranteed substitute for refrigerated storage. Sprinkling suitable outdoor surfaces can produce a related cooling effect, but should not be confused with water conservation or with making every surface safe immediately.

Moist air can rise, expand and cool. When it cools sufficiently, water can condense on tiny airborne particles. A visible cloud contains tiny liquid droplets and/or ice crystals—not merely invisible water vapour. Droplets or ice particles that grow large enough can fall as precipitation; rain, snow and hail involve different conditions.

Activity 8.10 investigates cloud formation in a bottle using pressure changes, water and particles. Treat the version involving a burning paper fragment as a teacher-led demonstration, not an unsupervised instruction. Compare what changes with and without added particles; pressure-related cooling and condensation, rather than smoke being water vapour, explain the intended observation.

Activity 8.11 connects oceans, rivers, lakes, clouds and groundwater. Water is stored in different places and travels by several routes. Sunlight supplies energy for evaporation; gravity drives falling precipitation and downhill flow. Groundwater occupies spaces in soil and rock; it is not necessarily an underground river.

Water cycling does not mean unlimited clean water is available where people need it. Much of Earth’s water is salty, and usable freshwater can be limited by location, season and pollution. Avoid wastage, repair leaks and protect water sources; treatment is still needed where water is unsafe.

Use these prompts to revisit the chapter’s ten end questions and further-learning activities. Explain the process and the evidence instead of memorising a word without its direction of change.

1. Changing state and natural ice

   Name the gas-to-liquid change; give household examples of both evaporation and condensation. Locate naturally solid water in snow, hail and glaciers, and distinguish it from the liquid droplets in dew.

2. Paint, ink and marks on paper

   Liquid paints and inks may dry as a liquid component evaporates and/or enters the paper. Crayon and pencil marks do not depend on drying a water layer. Formulations differ: do not assume all paints and ballpoint inks use the same liquid or drying process.

3. Grass, fans and a hot seat

   Moist natural grass can lose water by evaporation and transpiration; plastic grass lacks those processes. Sunlight and materials also affect surface temperature. Explain fan-assisted drying. For a hot seat, moving it into shade and allowing it to cool is safer than testing it with bare skin.

4. Drying is not complete waste treatment

   Drying wet sludge removes water and can reduce the mass and cost of transport. It does not by itself establish that pathogens or harmful pollutants have been removed. Any agricultural reuse needs appropriate treatment and assessment; a few days of drying are not proof that sewage sludge is safe manure.

5. A small observation record

   Choose a drying or condensation example, predict the change, and record time, conditions and what you actually see. Compare a wet and dry hand in moving air, or trace several possible routes of a water droplet. The book’s games and role-play can become short retrieval prompts; no invented observations are required.

6. Other liquids and responsible water use

   Alcohol can evaporate as well as water; this does not make every liquid safe to experiment with. Explain why conserving clean water remains necessary even though the water cycle continues.

Choose an explanation, check it, then return to the relevant concept if needed. These are original learning checks, not claimed UPSC previous-year questions.