Separating Techniques

Question 1

What is simple distillation used for?

Answer 1

To separate a liquid and soluble solid from a solution (e.g. water from a solution of salt water)

Question 2

How do you carry out simple distillation?

Answer 2

Solution is heated and water vapours will rise and evaporate
Water vapours will pass through the condenser, where it cools and condenses, turning into a liquid that will be collected in a beaker
After all the water is evaporated from the solution, the solute will be left behind

Question 3

What is fractional distillation used for?

Answer 3

To separate two or more liquids that are miscible with one another (e.g. ethanol and water from a mixture of the two)

Question 4

How do you carry out fractional distillation?

Answer 4

Solution is heated at temperature of substance with the lowest boiling point
This substance will rise and evaporate, and vapours will pass through a condenser, where it cools and condenses, turning into a liquid that will be collected in a beaker
All of this substance is evaporated and collected, leaving behind a mixture or a substance
For water and ethanol: Ethanol has a boiling point of 78°C and water of 100°C. The mixture is heated until it reaches 78°C, the ethanol boils and distils out of the mixture and condenses into the beaker. When temperature starts to increase to 100°C heating should be stopped. Water and ethanol are separated

Question 5

What is filtration used for?

Answer 5

To separate an undissolved solid from a mixture of the solid and a liquid / solution (e.g. sand from a mixture of sand and water)

Question 6

How do you carry out filtration?

Answer 6

Filter paper is placed in a filter funnel above another beaker
Mixture of insoluble solid and liquid is poured into the filter funnel
Filter paper will only allow small liquid particles to pass through as the filtrate
Solid particles are too large to pass through the filter paper so will stay behind as a residue

Question 7

What is crystallisation used for?

Answer 7

To separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g. copper sulphate from a solution of copper (ii) sulphate in water)

Question 8

How do you carry out crystallisation?

Answer 8

Solution is heated, allowing the solvent to evaporate to leave a saturated solution. Test the solution is saturated by dipping a clean, dry, cold glass rod into the solution. If the solution is saturated, crystals will form in the glass rod.
Saturated solution is allowed to cool and solids will come out of the solution, as the solubility increases, and crystals will grow
Crystals are collected by filtering the solution. Then the crystals are washed with cold, distilled water to remove impurity. Dry the crystals.

Question 9

What is paper chromatography used for?

Answer 9

To separate substances that have different solubilities in a given solvent (e.g. different coloured inks that have been mixed to make black ink)

Question 10

What is the mobile and stationary phase?

Answer 10

Mobile - where the molecules can move

Stationary - Where the molecules can’t move

Question 11

How do you carry out paper chromatography?

Answer 11

Pencil line is drawn on chromatography paper and spots of ink / dye is placed on it.
Paper is lowered into a bucket of solvent, allowing the solvent to travel up the paper, taking some of the coloured substances with it.
Different substances will have different solubilities so will travel at different rates, causing the substances to spread apart. Those with higher solubility will spread more than the others.
This will show the different components of the ink / dye.

Question 12

How do you calculate the Rf value?

Answer 12

distance travelled by solute/ distance travelled by solvent

Question 13

What does filtration do to seawater?

Answer 13

This process removes large insoluble particles by passing the water through layers of sand and gravel filters that trap larger particles.
Wire mesh filters are sometimes used, depending on the level of impurities in the water.

Question 14

What does sedimentation do to seawater?

Answer 14

Large insoluble particles sink to the bottom of a tank of water that has been left still for some time.
Iron sulfate or aluminium sulfate is sometimes added to help the fine particles clump together.

Question 15

What does chlorination do to seawater?

Answer 15

This process is used to kill bacteria and microorganisms which are too small to be trapped by the filters.
Cholera and typhoid are examples of bacterial diseases which can arise by the consumption of untreated water.

Question 16

How do you make portable water?

Answer 16

This process is done in some areas of the world where very hot and dry climates prevail and where a lack of water.
Sea water contains mainly salts and can therefore be distilled to separate the water and the salts.
The salt remains in the liquid while the steam is cooled and condensed to make potable water.
The process is extremely expensive as a lot of energy is required to heat the large volumes of water to 100ºC.
The wastewater produced is also extremely toxic due to the very high concentration of salts and must be disposed of correctly.