Separation techniques- Chemistry Topic 1

Question 1

What are compounds ?

Answer 1

Two or more elements combine chemically

Question 2

What is a mixture ?

Answer 2

A mixture consists of 2 or more elements or compounds not chemically together

Question 3

Separation techniques

Answer 3

Filtration
Crystallisation 
Simple distillation
Fractional distillation
Chromatography

Question 4

describe and explain simple distillation

Answer 4

Simple distillation is used to separate liquid from a solution.

The solution is heated. The part of the solution that has the lowest boiling point evaporates first
The vapour is then cooled, condenses and is collected
The rest of the solution is left behind in the flask

Question 5

What is the problem with simple distillation?

Answer 5

You can only use it to separate things with very different boiling points - if the temperature gets higher than the boiling point of the substance with the higher boiling point, they will mix again

Question 6

What is fractional distillation ?

Answer 6

Fractional distillation is used to separate a mixture of liquids

Question 7

Explain the process of fractional distillation

Answer 7

Place your mixture in a flask and stick a fractionating column on top.
Then heat it
The different liquids will all have different boiling points- they will evaporate at different temperatures
The liquid with the lowest boiling point evaporates first.

Question 8

What is paper chromotography?

Answer 8

Used to separate different dyes in an ink

Question 9

Explain the process of paper chromatography

Answer 9

1. Draw a line near the bottom of the sheet of filter paper - make sure you use a pencil as its insoluble and won’t dissolve in the solvent
2. Add a spot of the ink to the line and place the sheet in a beaker of solvent (water)
3. The solvent used depends on what’s being tested. Some compounds dissolve well in water however sometimes other solvents like ethanol is needed.
4. Make sure the ink isn’t touching the solvent- don’t want it to dissolve into it
5. Place a lid on top of the container to stop the solvent evaporating.
6. The solvent seeps up the paper, carrying the ink with it.
7. Each different dye in the ink will move up the paper at different rates so the dyes will separate out, Each dye will form a spot in a different place.
8. If any of the dyes are insoluble in the solvent used, they will stay on the base line.
9. When the solvent has nearly reached the top of the paper, take the paper out of the beaker and leave it to dry.
10. The end result is known as a pattern of spots called chromatogram.

well done!!!

Question 10

When is filtration used?

Answer 10

It separates solids from liquids.
It’s used if your product is an insoluble solid that needs to be separated from a liquid reaction mixture.
Used in purification too.

Question 11

What are the ways to separate soluble solids from solution?

Answer 11

Evaporation and Crystallisation

Question 12

Describe one of the ways to separate soluble solids from solution. (E)

Answer 12

Evaporation:
Pour the solution into an evaportating dish.
Slowly heat the solution. The solvent will evaporate and the solution will get more concentrated. Eventually crystals will start to form.
Keep heating the evaportating dish until only dry crystals remain.

Question 13

When can you use evaporation?

Answer 13

You can only use it if the salt doesnt decompose whrn its heated.

Question 14

Describe one of the ways to separate soluble solids from solution.(C)

Answer 14

Crystallisation:
Pour the solution into an evaporating dish and gently heat the solution. Some of the solvent will evaporate anf the soluton will get more concentrated.
Once some of the solvent has evaporated OR when you see crystals start to form, remove the dish from the heat and leave the solution to cool.
the salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution.
Filter the crystals out of the solution, and leave them in a warm place to dry. You could also use a desiccator