Filtration, decantation and evaporation

Introduction to simple separation

Imagine you are at home and you accidentally drop a handful of sand into a bowl of water. You cannot just pick the sand out with your hands. In Chemistry, we use special methods called separation techniques to get substances back from mixtures.

Decantation is the easiest method. It is like when you are washing rice or beans at home. You let the heavy dirt settle at the bottom, then you carefully pour out the water from the top without letting the rice fall out.

In simple terms, it is just 'pouring away' the top liquid while the heavy solid stays at the bottom.

Filtration is more professional than decantation. Think of using a sieve to strain 'papo' or 'akamu' or using a net to catch fish. In the lab, we use filter paper inside a funnel.

The solid that stays on the paper is called the residue, and the clean liquid that passes through is the filtrate.

Evaporation to dryness is used when you want to get a solid that has dissolved completely in water, like common salt. If you boil the salty water, the water turns to steam and leaves the salt crystals behind.

Use this method when you only need the solid and you do not mind losing the liquid to the air.

Steps for a mixture of sand and salt:

1. Add water to the mixture and stir so the salt dissolves.

2. Filter the mixture. The sand stays as the residue on the filter paper.

3. Pour the salt solution (filtrate) into an evaporating dish.

4. Heat the dish until all the water disappears, leaving the salt behind.

Example calculation for mass:

If an evaporating dish weighs 25.0g empty and 28.5g after evaporating a salt solution, what is the mass of salt? Mass of salt = Final weight (28.5g) - Empty weight (25.0g) = 3.5g.