A Journey through States of Water – Class 6 Science Chapter 8 Notes & NCERT PDF

Introduction

"If it does not rain well, even the mighty ocean will be drained." — Thirukkural

On a bright summer afternoon, Aavi and Thirav enjoy shikanji with ice. Thirav thinks ice and water are different substances because ice is hard and can be held, while water cannot. Aavi disagrees. When an ice cube is left in a cup (Activity 8.1), it turns into water — so ice and water are two forms (states) of the same substance. Water flows and splashes; ice does not. The chapter follows water on its journey through solid, liquid and gas and ends with the water cycle.

Key Concepts

8.1 Water's disappearing act – Evaporation

Rain puddles on the playground shrink by evening. Water left on washed utensils dries up. Where does it go?

Activity 8.2: Put a tablespoon of water on a steel plate and watch. Water does not seep through the steel, yet it disappears — it becomes water vapour, the gaseous state of water.

The process of conversion of water into its vapour state is called evaporation.

8.2 Another mystery – Condensation

Activity 8.3: Cold water with ice cubes in a glass tumbler — after five minutes, droplets appear on the outer surface. Aavi and Thirav debate: did water seep out? They reason step by step (Fig. 8.4) — the water level has not dropped; use a tall narrow bottle to notice tiny changes; test with room-temperature water.

When water vapour in the air comes in contact with a cold surface, it forms water droplets. The conversion of water vapour into its liquid state is called condensation.

Examples: dew drops on plants in the morning, water drops on the inside of a lid over boiling water.

Activity 8.4 (measuring evidence): Weigh the covered tumbler of ice water on a digital balance every 5 minutes for 30 minutes. The mass increases — extra water is collected from the air. Marking the water level shows the level does not go down, proving the water on the outside came from condensation, not seepage.

Humidity is the amount of water vapour in the air. Atmospheric Water Generators make drinking water by condensing water vapour from humid air.

8.3 States of water (Activity 8.5)

Other substances show these states too — wax, oil, ghee. Solids: stone, wood, glass. Liquids: milk, oil. Gases: oxygen, carbon dioxide. The smell of cooking reaches us because gases spread through air.

8.4 Changing the states of water

8.5 Faster or slower evaporation

Activity 8.7: Same amount of water in a bottle cap vs a plate. The plate dries faster → larger exposed area = faster evaporation. (Here we change the area, measure the time, and keep the amount and place the same — a fair test.)

Activity 8.8: Two identical caps with equal water, one in sunlight, one in shade → sunlight evaporates faster.

Conditions affecting evaporation:

8.6 Cooling effect

Aavi's new matka keeps water cold, unlike a steel pot. Water seeps through the porous clay and evaporates, producing a cooling effect. Other examples: sitting under a fan (sweat evaporates), sprinkling water on floors or roofs in summer, sanitiser feeling cold on hands, the surahi.

Activity 8.9 – pot-in-pot cooler: a small pot inside a large pot, gap filled with wet sand, covered with a lid or wet jute sack. Evaporation of water from the sand cools the inner pot — an electricity-free way to keep vegetables and fruits fresh for days.

8.7 How clouds give us rain

Activity 8.10: Squeeze and release a closed bottle with a little water. Add a tiny burnt piece of newspaper and repeat — haziness (a cloud) appears, because smoke particles give water vapour something to condense on.

Water cycle: Water from oceans and the Earth's surface evaporates into the atmosphere as vapour, condenses into clouds and returns as rain, hail or snow, ultimately flowing back to the oceans.

Only a small portion of Earth's water is usable; most is in oceans. With rising population and demand, we must use water wisely and keep water bodies clean.

Key Terms

Real-life Connections

Common Misconceptions

Keep the Curiosity Alive (Exercise Hints)