6. Separating Mixtures

Question 1

Separating by Selection

Answer 1

• Separation of solid/solid mixtures
• Hand picking out seperate components. Or using a sieve to seperate substances of different sizes.

Question 2

Separation by Flotation

Answer 2

• Separates solid/solid mixtures
• Separation by flotation: Solid mixture is added to a liquid where the components of the mixture do not dissolve. The liquid allows one solid component to sink, and the other solid component to float. The floating component can be skimmed off and dried, the other can be recovered by removing the liquid. This process is useful in the extraction of metal ores from soil.

Question 3

Magnetisation as a means of separation

Answer 3

• Separating solid.solid mixtures
• To simply separate a mixture of brass and iron screws, a magnet will pick out the iron ones.

Question 4

Decanting

Answer 4

• Muddy water has tiny particles of sediment.
• If the water is left to sit, the sediment sinks to the bottom, clear water cna be separated, this separates any liquid from a heavy insoluble sediment.

Question 5

Dissolving and then Filtering

Answer 5

• Separating solid/solid mixture
• In a mixture of two solids, if one is soluble in a liquid and the other one is not, the insoluble one will be left as a residue on a filter paper when the liquid passes through.

Question 6

Filtering

Answer 6

• Separates liquid/solid mixtures
• Filtering separates a liquid and undissolved solid using a fine sieve in the form of filter paper.
• Filtering under gravity is time consuming, a filter pump will reduce the pressure inside the flask and increase the rate at which liquid is forced through the filter paper by the atmospheric pressure.

Question 7

Centrifuging

Answer 7

• Separates solid/liquid mixture
• Separates solid particles dispersed in liquid medium, e.g., blood cells and plasma. The liquid sample is rotated very fast. Components are separated due to the centrifugal force, based on their density difference.

Question 8

Evaporation and Crystalisation

Answer 8

• Separates solid/liquid mixtures
• Separates a dissolved solid from its solvent. E.g when sea water is evaporated, solvent evaporates and solute is left behind, separating water and walt.

Question 9

The separating funnel

Answer 9

• Separate liquid/liquid mixtures
• Some liquids do not mix and are said to be immiscible. For example water and oil. Use a separating funnel to separate immiscible liquids, the more dense of the liquids will form the lower lay, the less dense solvent will float to the top. Opening the tap will remove the liquid.

Question 10

Simple Distillation

Answer 10

• Separate liquid/liquid mixture
• In a simple distillation, a homogeneous liquid mixture is boiled. The rising vapor then enters the inner chamber of a water-cooled condenser. The vapor condenses to a liquid, called the distillate, which is then collected in a separate vessel.
• Vaporising a liquid then condensing the vapour.
• Seperates two liquids of differing boiling points or separates a pure liquid from a solid dissolved in it.

Question 11

Fractional Distillation

Answer 11

• Separates liquid/liquid mixture
• Fractional distillation involves the separation of miscible liquids. The process involves repeated distillations and condensations and the mixture is usually separated into component parts (fractions). The separation happens when the mixture is heated at a certain temperature where fractions of the mixture start to vaporize.