Date post: | 25-Jan-2017 |
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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)