Topic 1 Separation techniques

Question 1

What does filtration separate

Answer 1

Insoluble solid from a liquid reaction mixture

Question 2

What can filtration be used for

Answer 2

Purification e.g solid impurities in the reaction mixture can be separated out using filtration

Question 3

What does insoluble mean

Answer 3

Can’t be dissolved in a liquid

Question 4

What 2 methods separate soluble solids from solutions

Answer 4

Evaporation and crystallisation

Question 5

Method of separating using evaporation

Answer 5

Pour the solution into an evaporating dish
Slowly heat the solution - the solvent will evaporate and the solution will get more concentrated and crystals will start to form
Keep heating the evaporation dish until all you have left are dry crystals

Question 6

Why might you not be able to use evaporation

Answer 6

Because some salts decompose when heated

Question 7

Method of Separating using crystallisation

Answer 7

1)Pour solution into evaporating dish and gently heat
(Some of the solvent will evaporate and the solution will get more concentrated
2) once some of solvent has evaporated or crystals start to form (point of crystallisation) remove dish from heat and leave solution to cool
3) salt should start to form crystals as it becomes insoluble in cold highly concentrated solution
4) filter the Crystals out of the solution and leave them in a warm place to dry
(Could use a drying oven if desiccator)

Question 8

Why else might you want to use crystallisation

Answer 8

Because it makes big crystals

Question 9

What is rock salt

Answer 9

Mixture of slat and sand

Question 10

Why can salt and sand be separated

Answer 10

Both salt and sand are compounds but salt dissolves in water and sand doesn’t
(Vital difference in physical properties)

Question 11

How can filtration and crystallisation be used to separate rock salt

Answer 11

1) grind the mixture to make sure the salt crystals are small and will dissolve easily
2) put mixture in water and stir(salt will dissolve but the sand won’t)
3) filter the mixture. Grains of sand won’t fit through the filter paper so will be collected. The salt passes through the paper as a part of the solution
4) evaporate the water from the salt so that it forms dry crystals

Question 12

What is simple distillation used for

Answer 12

Separating out a liquid from a solution

Question 13

Method of separating using simple distillation steps 1-3

Answer 13

1) solution is heated and the part of the solution with the lowest boiling point evaporates first
2) vapour is the cooled in the condenser and condenses back and is collected
3) the rest of the solution is left behind in the flask

Question 14

What can you use simple distillation for

Answer 14

To get pure water from sea water ( the water evaporates is condensed and collected , the salt is left behind)

Question 15

What is a disadvantage if simple distillation

Answer 15

Can only use it to separate substances with very different boiling points because if the temperature goes than the bp of the substance with the highest bp they will mix again

Question 16

What is fractional distillation used for

Answer 16

To separate a mixture of liquids (with similar bp)

Question 17

What and where is used to separate crude oil

Answer 17

Fractional distillation at a refinery

Question 18

Method of separating using fractional distillation

Answer 18

1) put mixture in a flask and attach a fractioning column on top ( then heat it)
2) different liquids have different bp so will evaporate at different temperatures
3) the liquid with the lowest bp will evaporate first and condense at the top of the fractioning column
4) liquids with higher bp will evaporate but will condense at the bottom as the top is too cool
5) When the first liquid has been collected, raise the temperature untill the next one reaches the top