Impurity facts for kids

An impurity means something is not completely pure. Imagine a glass of water that is super clean; we would call that pure water. If that water has dirt or tiny bits of other things in it, we would call it impure water. Having impurities can sometimes change how a substance behaves, like its melting point (the temperature it turns from solid to liquid) or its boiling point (the temperature it turns from liquid to gas).

Why Impurities Can Be Harmful

Sometimes, impurities can cause problems. For example, if the fuel in a car's engine is not pure, the engine might not work as well as it should. This can make the car run poorly or even damage the engine over time. In science, even tiny amounts of unwanted substances can affect experiments.

When Impurities Are Useful

Even though the word "impurity" sounds negative, impure materials can actually be very useful!

• Alloys: An alloy is a mixture of metals, or a metal mixed with another element. For example, steel is an alloy made mostly of iron with a small amount of carbon added. The carbon is an "impurity" to the iron, but it makes the steel much stronger and more useful than pure iron.
• Solar Cells: Solar cells, which turn sunlight into electricity, are often made from silicon crystals. For these cells to work, a very tiny amount of impurity (like 0.001% to 0.01%) is intentionally added to the silicon. These small additions help the solar cell create an electric current.

How to Remove Impurities

Scientists and engineers have different ways to remove impurities, depending on the material:

• For Liquids: Impurities in liquids can often be removed by a process called distillation. This involves heating the liquid until it turns into a gas, then cooling the gas back into a pure liquid, leaving the impurities behind.
• For Solids: Impurities in solids can sometimes be removed using recrystallization. This method involves dissolving the solid in a hot liquid, then letting it cool slowly. As it cools, the pure solid forms crystals, and the impurities stay dissolved in the liquid.