Separation Techniques

Question 1

A separating funnel should be used when you want to separate __________ liquids.

Answer 1

Immiscible

Question 2

When is magnetic separation used?

Answer 2

Used when separating magnetic material from a mixture with other non-magnetic materials

Question 3

How does evaporation to dryness work? What is a limitation of this separation technique?

Answer 3

The solution is heated until all the water is evaporated completely, leaving behind only the solid. However, a limitation to this method is that it cannot be used for solids that decompose on heating like sugar.

Question 4

What is a saturated solution?

Answer 4

A saturated solution contains the maximum amount of solute that can be dissolved in the solvent at a particular temperature

Question 5

How does crystallisation work?

Answer 5

It heats the solution till saturation. After which, it is left to cool to obtain the crystals.

Question 6

Name the steps for crystallisation.

Answer 6

1. Heat the solution till saturation
2. Allow the saturated solution to cool and pure solid crystals will form slowly
3. Filter to collect the crystals
4. Wash the crystals with cold distilled water and dry between sheets of filter paper

Question 7

How to decide whether to use evaporation to dryness or crystallisation?

Answer 7

If the solute decomposes on heating, use crystallisation. If not, use evaporation to dryness.

Question 8

Name the steps for sublimation.

Answer 8

1. Heat the mixture and the volatile compound will start to sublime
2. Place a cool funnel over the evaporating dish. The gaseous iodine will condense on the cool funnel and form pure iodine in solid state
3. Collect the iodine crystals

Question 9

Name the steps for simple distillation

Answer 9

1. Heat the solution in a round-bottomed flask for even heat distribution. Boiling chips are added to prevent vigorous movement of liquid which ensure smooth boiling
2. The water boils and water vapour rises and enters the condenser. The water vapour cools down in the condenser and is collected as a distillate
3. The distillate is collected in a conical flask to prevent spillage

Question 10

Name the steps for fractional distillation

Answer 10

1. Heat the mixture. The liquid with the lowest boiling point will be the first to be vaporised.
2. Its vapour will rise up to the top of the fractionating column, cooled as it passes through the condenser and be collected as the distillate. Ensure the temperature remains the same until all of first vapour has condensed.
3. Collect the distillate in the conical flask
4. Repeat the process and collect the different substances that were in the mixture

Question 11

Why should the starting line of a chromatogram be drawn with pencil instead of ink?

Answer 11

The ink may dissolve in the solvent, causing the results to be inaccurate