Separating mixtures

Separating mixturesMixtures can be easily separated.There are several different methods

depending on what is to be separated.Over the next few pages are several methods,

stick in the picture that goes with the notes.

Sieving:This is an easy way of

separating big from small. The small parts fall through the sieve.

Sorting:Another easy way to

separate a mixture. Works best if the objects are large enough to pick up easily. You can sort according to colour, size or shape etc.

magnetismThis is one of the easier methods to

separate metals from non-metals (or from non-magnetic chemicals)

The metal (usually iron) is attracted to the magnet.

 

Mini experimentUsing a magnet and plastic Petri dish,

separate iron filings from a mixture of sand and iron filings.

magnetIron filings

sandPlastic petrie dish

filteringThis is similar to sieving. It removes a solid

from a liquid. The pore sizes in the filter paper allow the liquid through but not the solid.

2 liquids can’t be separated in this way, only a liquid and a solid

  Mini experiment:Separating sand and water. Copy and complete

the work from the board

decantingThis is a way of removing a liquid from

a solid. Often used when there are solid particles that will sink to the bottom.

Decanting is also used when pouring off home brew beer so as not to get the solid particles floating in the bottom of the bottle in the drinking glass.

Task: follow the teachers instructions to have a go at decanting.

chromatographyIn paper chromatography, a liquid sample flows up

a vertical strip of adsorbent paper, on which the components (usually seen as colours) are deposited in different locations. Each colour comes to a halt at different heights because of the speed they travel.

Chromatography is used in forensics for many chemicals. E.g. deciding on pen inks, unknown smells etc. Each chemical has a signature, it always comes out of a mixture in the same place each time. Often on CSI programmes you will see this as peaks on a graph, with each peak representing a different chemical. 

evaporationThis method uses the sun or some other heat

source to remove water from a solution (dissolved solid e.g. salt). The solid is left behind as the water evaporates.

This is the method that is used to produce table salt in NZ from sea-water. At Grassmere the sea water is placed in large shallow pool, the sun (and wind) evaporate the water, leaving the salt behind. The salt is removed and dried further in the sun then prepared for sale. 

Distillation This method is used to separate 2 liquids, or

a dissolved solid from a liquid.Distillation works through the fact that

different liquids have different boiling points. The first liquid to reach boiling point turns into a gas and rises to the top of the distillation column, it is then cooled and becomes a liquid again and drips out of the condenser.

Draw the diagram off the board, it will take a full page.

Teacher demo:We can see distillation in the teacher demo. A

mixture of vinegar and water are to be separated using this method. Water boils at 100oC, whereas vinegar boils at 118oC. This means that the water will be the first to turn into a gas and will come out from the condenser.What came out of the condenser? _____________

With a home distillation unit, the idea is to produce pure water by separating tap water from the impurities in it. The water is evaporated and rises away from the impurities. The steam is then cooled and pure water occurs.

Problem:1. List the steps you would take to separate

out a mixture of sand, iron filings and salt. Describe how each step works to separate the three substances in the mixture.

2. Sand, saw dust, salt and water have been mixed together. Describe the steps you would take to separate and collect each of the substances. For each step, say how it works to separate out the substance

Pg 14 & 15 should be completed. Mark your own work.

Pg 16-17 complete and mark.No book: copy and complete the following:Write the name of the separation method:_______________: liquid is boiled off, leaving crystals

behind_______________: the colours in ink are separated

because they move at different speeds._______________: a magnet attracts particles of iron_______________: liquid is boiled off a solution and

condenses on a cold surface_______________: a liquid is separated from a solid

as it passes through filter paper