Learning Objectives
- Learn about things that dissolve in water and things that do not
- Understand the concepts of floating and sinking
- Explore how water behaves in different situations
- Develop curiosity through simple water experiments
Key Concepts
Things That Dissolve in Water
When you put sugar in water and stir, the sugar disappears. This is called dissolving. The sugar is still there (the water tastes sweet!), but it has mixed completely with the water. Salt, sugar, and some colours dissolve in water. Sand, chalk powder, and oil do not dissolve in water. A substance that dissolves is called soluble, and one that does not is called insoluble.
Floating and Sinking
Some things float on water and some things sink. A piece of wood, a leaf, and a plastic bottle float because they are lighter than the same amount of water. A stone, a coin, and an iron nail sink because they are heavier. A large ship floats even though it is very heavy because of its shape; it is hollow inside and spreads its weight over a large area.
Evaporation
When water is left in an open container, it slowly disappears. This is called evaporation. The water turns into water vapour and goes into the air. Wet clothes dry because the water in them evaporates. Evaporation happens faster in the sun, in wind, and when the water is spread over a larger area. This is why clothes dry faster on a sunny, windy day.
Water as a Solvent
Water can dissolve many substances, which is why it is called a universal solvent. When substances dissolve in water, they form a solution. Lemon juice mixed with water and sugar makes lemonade, which is a solution. Warm water dissolves things faster than cold water. Stirring also helps substances dissolve faster.
Important Terms
- Dissolve: When a substance mixes completely with water and seems to disappear
- Soluble: A substance that dissolves in water (like sugar, salt)
- Insoluble: A substance that does not dissolve in water (like sand, oil)
- Evaporation: Water changing from liquid to vapour and going into the air
- Solution: A mixture where a substance has dissolved completely in water
- Float: To stay on top of water without sinking
Quick Revision
- Sugar and salt dissolve in water; sand and oil do not
- Dissolving means mixing completely with water
- Light things float; heavy things sink
- Shape matters: hollow shapes float better than solid ones
- Evaporation makes water turn into vapour
- Warm water dissolves things faster than cold water