Separating mixtures and chemical reactions

Separating mixtures• There are 2 types of mixtures:

heterogeneous – we can see the individual substances that make it up

homogeneous – we can´t see the individual substances

We can separate substances in mixtures in different ways:

Magnetic separation

Decantation

Filtration

Evaporation

Distillation

Magnetic separation

• We can use it if we want to separate mixtures that consist of substances attracted by magnets and substances that are not

Decantation• When we decant a liquid, we

pour off the liquid so that sediment remains in the container• We can also use decantation

for two liquids of different density (for example, oil and water)

- heavy sediments in liquids sink to the bottom of a container

Filtration

• It is used for separating much smaller particles from a liquid or gas• A filter is used to catch the

particles, but allows the liquid to pass

Evaporation• It is used to remove water in salt evaporation ponds• Solids dissolved in a liquid can be separated using heat (the liquid

turns into vapour and the remaining sediment, the solids, can be collected)

Distillation• It is used to produce alcohol and in the petrochemical industry

• we use distillation when two liquids evaporate at a different rate (such as water and ethanol)

• The liquid is heated (ethanol evaporates first and forms vapour), this vapour is then collected and cooled, resulting in pure ethanol

Chemical reactions

• They change the properties of the original substance• A new substance is created

Combustion

Oxidation

Fermentation

Combustion (burning)• It is a chemical reaction that produces energy in the form of heat and

light• It can happen when oxygen from the atmosphere reacts with a fuel

(for example wood, gas, oil…)• when these fuels burn, the atoms in the substance react and form

new substances (such as ash and smoke)

Oxidation• Some metals (for example, iron) react when they are exposed to air

and the atoms are changed into a new substance rust (it has a brown colour)• Oxidation also occures in some foods (apples, potatoes…)

Fermentation• It is a chemical reaction where fungi or bacteria change organic

substances into other substances• During fermentation, fungi produce alcohol and bacteria produce

lactic acid• This chemical reaction is used to make cheese, bread, yoghurt, wine

and also to preserve food (fruit, vegetable, meat can be stored for longer)