Atomic Structure and the Periodic Table: Physical Separation Techniques

Question 1

What are the four types of physical separation techniques?

Answer 1

• filtration
• crystallisation
• distillation
• chromatography

Question 2

What are physical separation techniques used for?

Answer 2

They can only be used to separate mixtures. They cannot be used to separate elements in a compound.

Question 3

What is filtration used for?

Answer 3

Used to separate an insoluble solid from a liquid.

Question 4

How is filtration done?

Answer 4

1. mixture is poured into the filter paper
2. the liquid passes through the tiny pores in the filter paper (this liquid is known as the filtrate)
3. the solid material cannot pass through the filter paper so is trapped

Question 5

What is crystallisation used for?

Answer 5

used to separate a soluble solid from a liquid. eg an aqueous solution

Question 6

How is crystallisation done?

Answer 6

1. leave the solution for a few days
2. the water will evaporate leaving small solid crystals

Question 7

How can crystallisation be sped up?

Answer 7

This process can be sped up by heating the solution to evaporate the water. However certain chemicals will break down if heated so sometimes it’s better to allow the water to evaporate on its own.

Question 8

What is distillation used for?

Answer 8

used to separate a soluble solid from a liquid and keep the liquid (unlike in crystallisation)

Question 9

How is distillation done in two main steps?

Answer 9

1. evaporate the liquid by heating
2. condense the vapour back into a liquid by cooling

Question 10

Describe a method of distillation.

Answer 10

1. heat the solution for example using a bunsen burner
2. the liquid starts to evaporate and its vapour rises up the glass tube (which is attached to the flask containing the liquid)
3. the vapour passes into he condenser causing it to condense
4. the liquid is collected in the beaker
5. at the end, there will solid crystals in the flask and the liquid in the beaker

Question 11

What can simple distillation be used for? Why is this generally not done?

Answer 11

• simple distillation can be used to produce drinking water from seawater
• however this requires a lot of energy so is generally not used to produce drinking water

Question 12

What is fractional distillation used for?

Answer 12

Separating a mixture of liquids with different boiling points.

Question 13

How is fractional distillation done? (on a small scale)

Answer 13

1) Heat the solution
2) Both liquids will start to evapourate but the one with the lower boiling point will evapourate more easily.
3) The mixture of vapours enter the fractionating column and condense dripping bade into the flask where they evaporate again
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4) This repeated cycle of evaporation and condensation increases the amount of the lower boiling point chemical in the fractionating column.
5) As the wam vapours pass up the column, they reach the thermometer whose temperature begins to rise.
6) These vapours (a mixture of both but with more af the lower boiling point one) will pass into the condenser.
7) They will then turn back to a liquid.
8) This liquid is still a mixture of the chemicals.
9) The thermometer’s temperature will eventually stop rising and read the lower of the two boiling points. At this point there is now mainly only the chemical with the lower boiling point passing into the condenser.
10) This chemical can be collected in a beaker. This is the first fraction.
11) After a while, the temperature on the themometer begins to rise again. Meaning again a mixture of vapours containing mostly the chemical with the higher boiling point is passing into the condersor.

Question 14

If the two liquids have very similar boiling points then what may they require?

Answer 14

• much harder to separate
• may need to undergo several rounds of fractional distillation