Week 7

How do we separate mixtures?

learning intentions

investigate different ways to separate solids from solutions.
investigate different ways to separate mixtures, particularly homogenous mixtures (solutions)

success criteria

Identify and describe the process of decantation, sieving, filtration, gravity and magnets in separating substances.
Identify and describe the process of evaporation & crystallisation, distillation and chromatography.
Understand that separation of substances is based on the characteristics of the mixtures and use appropriate process to separate a mixture of sand, salt and iron filings.

Tasks

Knowledge & understanding

Separating Substances worksheet on Google Classrooms

Investigation Skills

Prac: sand, salt & iron filings separation

Knowledge and understanding

understanding the language

Components of mixtures are separated from each other using a property they have that is different.

Separating undissolved solids

If one of the components of the mixture is an insoluble solid (the other component might be another solid or liquid) then it can be separated using the following methods:

In decantation, the undissolved solid is allowed to settle to the bottom, then the liquid above it is poured off. In the manufacture of wine, the grape sediment settles and the wine is poured off before bottling. This is also done sometimes just before drinking the wine if there is a lot of sediment in the bottom of the bottle.

Sieves separate solid particles having different sizes. Sieves come in all forms like flyscreens on doors, serving spoons with holes in them to drain food juices, flour sieves and fising nets, grids across the openings of stormwater drains filter rubish to prevent it going into waterways.

Filtration involves pouring a mixture through a filter paper (which is acting like a very fine sieve) to catch the undissolved solids (the residue) in the paper and the liquid components (the filtrate) in a container below the filter funnel.

In centriuging the mixture is placed in a container and spun at very high speeds. Centrifuging can be used to separate suspended solid particles from the liquid they are suspend in.

The more denser the solid particles are, they move to the bottom of the centrifuge. Blood gets centrifuged to separate the plasma from the red blood cells.

Using gravity, if a mixture of insoluble solids is shaken with water, the more dense particles settle on the bottom. Panning for gold uses gravity separation.

Magnets will separate a magnetic solid from non-magnetic solids. Scrapyards use large electromagnets to separate iron from other types of metal.

separating solutions

Dissolved substances can be separated from their solvent by the following method.

Evaporation and crystallisation are used to separate a dissolved solid from it's solvent. The solution is heated until it boils and is then allowed to evaporate. As the solvent evaporates the solution becomes more and more concentrated, until it is eventually saturated. At this point crystals of the solute start to form. In this separation, the solvent is 'lost' into the air. Large-scale production of salt from salt water is done using large, shallow salt pans and the sun to evaporate the water to leave the salts behind.

Murray River salt pans

Laboratory evaporation with a Bunsen burner and watch glass

Distillation is the same process as in evaporation and crystallisation except that the solvent vapours are condensed and collected in a separate container. Both solute and solvent are collected. Distillation can be used to obtain pure water from sea water or other impure water sources

Distillation of whiskey - the alcohol produced from the fermentation of malted (sprouted) barley is then concentrated by distillation.

Laboratory distillation equipment

Chromatography separates different solutes dissolved in the same solute (two or more liquids). It is more often used to identify the components in a mixture rather than to separate them. Chromatography separates different solutes on the basis of their different solubility in the solute. Chromatography is often used in forensic science to determine what substances have been dissolved in a particular mixture.

Gas chromatography–mass spectrometry (GC–MS) is an analytical method that combines the features of gas-chromatography and mass spectrometry to identify different substances within a test sample

Chromatography experiment

separating substances

Prac: Work out how to separate a mixture of sand, salt and iron filings.

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