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Introduction to States of Water
- Water exists in three forms or states: solid (ice), liquid (water), and gas (water vapor).
- Each state has unique properties that make it act differently.
- Ice can be held, but water flows freely. Are they different substances? Are they same substance in different forms?
Observing Ice and Water
Activity: Melting Ice
- Objective: To observe how ice changes to water.
- Steps:
- Place an ice cube in a cup and let it melt.
- Result: The ice turns into water.
- Conclusion: Ice and water are the same substance in different forms or states.
Water Disappearing from Puddles
- Observation: Water puddles disappear after rain. Has it absorbed by the soil?
- Explanation: Actually water turns into a gas (water vapor) and mixes with air, a process called evaporation.
Evaporation
- Definition: Evaporation is the process where water changes from a liquid to a gas (vapor). It happens even at room temperature.
- Example:
- Wet clothes drying in the sun.
- Mopped floors drying.
- Sweat evaporating from our bodies.
Activity: Observing Evaporation
- Objective: To see evaporation in action.
- Steps: Place a tablespoon of water on a steel plate and observe as it disappears.
- Result: The water changes into vapor and disappears.
Water Droplets on Cold Surfaces
- Observation: Droplets form on the outside of a glass filled with cold water and ice.
- Explanation: Water isn’t leaking from the glass; it’s forming from air vapor. This is due to condensation.
Condensation
- Definition: Condensation is the process where water vapor in the air cools and turns back into liquid droplets.
- Example: Foggy bathroom mirrors after a hot shower.
Experiment: Observing Condensation
- Objective: To understand condensation.
- Steps: Place a glass of cold water with ice on a weighing scale, cover it, and check the weight over time.
- Result: The weight increases as water droplets form on the outside of the glass, showing condensation.
The Three States of Water
- 1. Solid (Ice):
- Has a fixed shape and does not flow or spread.
- Stays solid even when moved between containers.
- 2. Liquid (Water):
- Water takes the shape of the container it’s in but has a constant volume.
- It flows and can spread over surfaces.
- 3. Gas (Water Vapor):
- Spreads out in all directions and fills any available space.
- Even though we can’t see it, water vapour is present in the air.
Examples: Other substances can also be found in different states, like:
- Solids: Stones, wood, glass
- Liquids: Milk, oil
- Gases: Oxygen, carbon dioxide
Changing States of Water
Water can change from one state to another:
1. Melting: Ice to water
- Happens when we heat ice.
2. Freezing: Water to ice
- Happens when we cool water in a freezer.
3. Evaporation: Water to water vapour
- Happens when water is heated, like on a hot day.
4. Condensation: Water vapour to water
- Happens when water vapour cools, like water droplets on a cold glass.
Examples:
- Wax: Changes from solid to liquid when heated and back to solid when cooled.
- Coconut oil: Can turn solid in cold weather and melts in warm weather..
Collecting Water from Air
Atmospheric Water Generators (AWG): Machines that collect water from humid air by cooling it, which makes water vapour condense into drinkable water. This is similar to how water droplets form on a cold glass.
Conditions That Affect Evaporation
- Temperature: Water evaporates faster on hot days than on cold ones.
- Wind: Water evaporates faster as moving air helps.
- Surface Area: Water evaporates quicker when spread over a large surface. The larger the area (like a plate), the faster it evaporates.
- Humidity: High humidity slows down evaporation because the air is already full of water vapor.
Activities to Observe Evaporation
Activity 8.7: Compare evaporation time of water in a bottle cap vs. a plate.
Activity 8.8: Observe water evaporation in sunlight vs. shade.
Cooling Effect of Evaporation
- Evaporation and Cooling: Evaporation absorbs heat, creating a cooling effect.
- Example: Water in an earthen pot (matka) stays cool because of slow evaporation.
- Fan Effect: Sitting under a fan helps sweat evaporate faster, making us feel cool.
Make a Pot-in-Pot Cooler
- Place a smaller pot inside a larger one with sand in between.
- Pour water in the sand and cover; after a few hours, it cools inside.
Pot-in-Pot Cooler working mechanism
The pot-in-pot cooler uses evaporative cooling to keep items inside cool without electricity. Here’s how it works:
- Structure: A small earthen pot is placed inside a larger pot, with a layer of sand between them.
- Water Absorption: The sand between the pots is filled with water. Since the earthen pots are porous, they allow water to seep slowly from the sand to the outer surface of the larger pot.
- Evaporation Process: The water on the pot’s outer surface evaporates into the surrounding air. This process requires heat, which is taken from the pots and the items inside, causing a drop in temperature.
- Cooling Effect: As evaporation continues, heat is drawn out continuously, keeping the air inside the inner pot cooler than the surroundings.
This cooling effect is similar to how sweating cools the human body. The process is most effective in dry and warm climates, where evaporation happens quickly.
How Clouds Give Us Rain
- Cloud Formation (Condensation) : Water vapor rises, cools, and turns into tiny droplets, forming clouds.
- Clouds: Formed from small droplets around dust particles.
- Rain: When droplets in clouds become heavy, they fall as rain (or as snow/hail in colder weather).
The Water Cycle
- Process: The water cycle describes how water moves through evaporation, condensation, and precipitation.
- Evaporation: Water from oceans, rivers, and lakes turns into vapor and rises.
- Condensation: Water vapor cools and forms clouds.
- Precipitation: Water falls back to Earth as rain, snow, or hail, completing the cycle..
Importance: The water cycle is essential for replenishing Earth’s fresh water supply.
Using Water Wisely
- Save Water: With rising demand, it’s essential to avoid water waste.
- Prevent Pollution: Keep water sources clean and conserve this nature’s treasures.
