Evaporation

Evaporation is how we get salt out of seawater. This 90-second narrated lesson teaches kids what happens when water turns into vapour, why the dissolved solid is left behind, and where in the real world this method is used. Includes a quick quiz.

Class 6 ScienceClass 6 / Grade 6Ages 8–11
Lesson
🧂 Evaporation
Salty water — get the salt back?🧂 dissolvedSieve won't catch the salt — it's mixed into the water.

Here's a tricky one. You stir salt into a glass of water. The salt vanishes — it dissolves. The water now looks completely clear. So how do you get the salt back? A sieve won't help. A filter won't help. The salt is hiding inside the water itself.

What is evaporation?

Evaporation is what happens when a liquid slowly turns into a gas (vapour) and floats away into the air. It happens to all liquids, but most often we talk about water — water in a wet floor, in a pond, on the surface of clothes drying on a line. The faster you heat water, the faster it evaporates. The sun does it slowly; a stove does it quickly.

How is evaporation a method of separation?

Imagine you stir salt into water. The salt dissolves — it becomes part of the liquid, mixed in so tightly that you can't see it. A sieve won't catch it. A filter won't catch it. So how do you separate the salt from the water?

You can heat the water. The water slowly turns into vapour and rises into the air. But salt can't turn into vapour — it stays right where it is. Bit by bit, all the water disappears, and beautiful white salt crystals are left at the bottom of the pan. That's how evaporation separates a dissolved solid from a liquid.

Where is evaporation used in real life?

  • Sea-salt pans — Indian salt-makers in Gujarat, Tamil Nadu and Andhra Pradesh fill huge shallow rectangular ponds with seawater. Over weeks of strong sunlight, the water evaporates and salt crystals are scraped off the bottom. India is one of the world's biggest salt producers, almost entirely through this method.
  • Sugar from sugarcane — sugarcane juice is heated in large pans. Water evaporates; the sugary solid that's left becomes jaggery (gur) or, with more processing, white sugar.
  • Crystal jewellery — gemstones like rock-salt crystals or copper sulphate are grown by evaporating their solutions slowly.
  • Fertiliser and chemical factories — many useful solids are extracted from solution using evaporation.

Evaporation in nature

Evaporation isn't just for separating things — it's part of the water cycle. The sun heats lakes, rivers and oceans every day, and water vapour rises into the sky. There it cools, condenses into clouds, and eventually falls back as rain. This cycle is what keeps fresh water moving around the planet.

Frequently asked questions

What's the difference between evaporation and boiling?

Boiling is when water gets so hot that bubbles of vapour form throughout the liquid — usually 100°C. Evaporation can happen at ANY temperature, just from the surface, and is much slower. A puddle drying in the sun is evaporation; water bubbling on a stove is boiling.

Why doesn't the salt evaporate too?

Salt has a much higher boiling point than water — over 1400°C. Long before the salt would evaporate, all the water has already turned into vapour. So the salt is left behind as crystals.

Can you get drinking water from seawater this way?

Yes! It's called distillation. You boil seawater, catch the vapour in a cool pipe, and let it condense back into liquid water. Salt stays behind in the original pan, fresh water drips out the other end. Big desalination plants use this idea on a huge scale.

Why is evaporation faster on a sunny day?

Two reasons. Heat — sun warms the water and gives molecules energy to escape into the air. Wind — air currents blow the vapour away so more can rise. That's why washing dries fastest on a sunny, breezy day.

Is evaporation reversible?

Yes — when water vapour cools (in the sky or on a cold mirror), it turns back into liquid water. That's called CONDENSATION. Together, evaporation and condensation drive the entire water cycle.

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