Evaporation

 

What is evaporation?

Evaporation is when a liquid changes into a gas slowly, without reaching its boiling point.

Evaporation can happen at any temperature, but boiling only happens at a specific temperature for each liquid.

 

 

Using evaporation to separate a solution

Evaporation can be used as a separation method to separate components of a mixture with a dissolved solid in a liquid. The liquid is evaporated, meaning it is converted from its liquid state to gaseous state. This often requires heat. Once the liquid is completely evaporated, the solid is all that is left behind.

 

 

A solution is placed in an evaporating dish and heated with a Bunsen burner.

 

Crystallisation

Crystallisation is a way of separating a solid solute from a solution by letting the solvent (water) evaporate slowly over time.

Crystallisation makes the solute form bigger crystals, because the slower the water evaporates, the more time the solute has to arrange itself into a regular pattern.
These are the steps for crystallisation:

 

• Instead of heating the evaporating basin directly with a Bunsen burner, it is often better to heat it gently and slowly over a beaker of boiling water.
• Heat the solution until only half of the water is left, which makes the solution more concentrated. Leave the solution to cool down and large crystals will grow slowly.
• Put the evaporating basin in a warm place so the rest of the water evaporates.

 

Summary:

 

• Evaporation is when a liquid changes into a gas slowly, without reaching its boiling point.
• Crystallisation is a way of separating a solid solute from a solution by making crystals.
• When a solution is heated, the liquid solvent goes away and the solid solute stays as crystals.