Separation And Purification

Question 1

FILTRATION

Answer 1

• used to separate insoluble particles from a liquid

Question 2

FILTRATION PROCEDURE

Answer 2

1. Pour the mixture into a filter funnel that is lined with filter paper
2. Collect the filtrate in a conical flask
3. Collect the residue and dry in a piece of filter paper

Question 3

EVAPORATION TO DRYNESS

Answer 3

• used to obtain a soluble solid from a solution by heating the solution until all the water has boiled off.
• solid obtained is not always pure. When all the water has been removed, any soluble impurities will be left together with the solid

Question 4

CRYSTALLISATION

Answer 4

• used for obtaining a pure solid sample from its solution

Question 5

CRYSTALLISATION PROCEDURE

Answer 5

1. Dissolve the impure copper (II) sulfate crystals in water
2. Filter to remove any insoluble impurities. Collect the filtrate which is copper (II) sulfate solution.
3. Heat the copper (II) sulfate solution until it is saturated
4. When the solution is saturated, leave it to cool and crystallise
5. Filter to collect the crystals. Wash the crystals with some cold distilled water to remove the impurities. Dry the crystals between a few sheets of filter paper.

Question 6

PURE SUBSTANCE

Answer 6

• made up of one single element or compound.

- it is not mixed with any other substance

Question 7

SUBLIMATION

Answer 7

substances that sublime:

• iodine
• naphthalene
• solid carbon dioxide

Question 8

SIMPLE DISTILLATION

Answer 8

used to separate a pure solvent from a solution

• in the distillation flask, the solution boils. Boiling chips are added to ensure smooth boiling. Water vaporises, rises and enters the condenser.
• in the condenser water vapor is cooled. The vapor condenses and changes back into pure water.
• pure water is collected as a distillate in the conical flask
• the salt solution, which remains in the distillation flask, becomes more concentrated as distillation continues. If distillation is allowed to carry on, a solid reside of salt will be left in the flask

Question 9

PRECAUTIONS TAKEN DURING DISTILLATION

Answer 9

Thermometer - bulb of thermometer should be paced beside the side arm of the distillation flask. It should not be dipped into the solution. This ensures that the thermometer measures the booing point of the substance that is being distilled.

Condenser - slope downwards. COD water is allowed to enter water jacket from bottom to leave from the top. This ensures that the pure solvent formed runs downward into the receiver. If water enters from the top of the condenser, it will exit before it can be completely filled. Thus water has to enter the denser from the bottom to ensure that the entire jacket is always completely filled. This provides a more efficient cooling system.

Receiver - if the distillate is volatile, the received can be put into a large container filled with ice. This helps to keep the temperature of the distillate low so that it remains in the liquid state.

Question 10

What is a Separating funnel used for?

Answer 10

A separating funnel can be used to separate immiscible liquids.

Question 11

SEPARATING FUNNEL PROCEDURE

Answer 11

1. Pour the mixture of oil and water into the separating funnel
2. Support the separating funnel using a retort stand. Then place a clean beaker below the separating funnel.
3. Allow the liquids to separate completely. This may take some time. The denser liquid will be the bottom layer.
4. Open the tap of the funnel to allow the bottom layer to drain into the beaker. Close the tap before the top layer of liquid runs out
5. Place another beaker below the funnel. Open the tap to allow a little of the top layer of liquid into the beaker. Dispose of the liquid collected. Now the separating funnel contains only oil while the beaker from step 4 contains only water.

Question 12

USE OF FRACTIONAL DISTILLATION

Answer 12

• to separate a mixture of miscible liquids with different boiling points

Question 13

PROCESS OF FRACTIONAL DISTILLATION

Answer 13

• the liquid with the lowest boiling point will distil over first
• the vapors of liquids with higher boiling points condense along the fractionating column and fall back into the round bottomed flask

Question 14

INDUSTRIAL APPLICATIONS OF FRACTIONAL DISTILLATION

Answer 14

• obtain nitrogen, argon, oxygen from air
• separate petroleum into useful fractions
• obtain ethanol produced by the fermentation of glucose solution

Question 15

CHROMATOGRAPHY

Answer 15

• the method of separating two or more components that dissolve in the same solvent.

Question 16

Rf value

Answer 16

Distance travelled by substance / distance travelled by solvent

Question 17

Uses of chromatography

Answer 17

• separate components in a sample
• identify the components present in a simple
• identify substances
• determine whether a substance is pure

Question 18

When do we know if a substance is pure?

Answer 18

• substance is pure when it has an exact and constant melting and boiling point

Question 19

What are effects of impurities on boiling point?

Answer 19

• increase boiling point of a liquid. The greater the amount of impurities, the higher the boiling point.
• impurities cause boiling to take place over a range of temperatures