Separating mixtures: how we concentrate
natural materials: teachers’ notes
Level
This activity is designed for students aged 11-14.
Topic
The activity covers methods of separation of mixtures as a class practical and then
applies ideas about separation to separating mixtures of minerals on the basis of
their different physical properties.
Description
Students are shown a piece of granite and see that it is clearly a mixture. They are
then presented with several simple mixtures and invited to devise and try out ways of
separating them. Finally the ways in which some real mixtures of minerals are
separated are discussed and tested.
Context
Students should have already done some work on separating mixtures in which case
the teacher will probably wish to stress the mineral separation aspect.
Teaching points
It is important to stress to students the principle that in order to separate the
components of a mixture, there must be a property difference between the
components.
Timing
Two approximately one-hour teaching periods.
Apparatus
Eye protection
Tweezers
A large, shallow plate made from metal or plastic.
Small magnets (wrapped in Clingfilm™ to make removal of iron filings easier).
Access to standard laboratory apparatus including beakers, flasks, funnels
(and filter paper) Bunsen burners, tripods, gauzes, heatproof mats.
An ultraviolet lamp.
A bucket.
A ‘jigger’, made from a 30 cm length of hard transparent plastic tube, of about
3
cm internal diameter, with a piece of 1 mm metal gauze stuck to the bottom.
(Heat the gauze to red heat, then quickly press the plastic tubing onto the
gauze and leave it to cool.)
A ‘buddle’ made from an approximately 2 m length of square cross-section
plastic guttering. Into this are glued at roughly 15 cm intervals 1 cm high
Figure 2 The composition of granite (modified from an original image by
permission of the Utah State Office of Education)
The black or grey shiny mineral is called mica. (Mica is a mineral that can be used in
the small windows in central heating boilers as it can withstand great heat. It can be
made into vermiculite, which is used as loft insulation.)
The shiny, glassy and colourless mineral is quartz (Quartz is used in some types of
watches and for making prisms, in glassmaking and in abrasives.)
The white, creamy or pink mineral is called feldspar and is used in the ceramic
(pottery) industry as an additive to the clay.
Point out that to use these components, a method of separating mixtures is required.
Now give the class a set of mixtures and ask them to devise ways in which they
could be separated using standard laboratory equipment. They may try out any
methods that they suggest provided that they are safe and sensible.
Mixtures include (with a possible separation method in brackets):
Marbles of two different colours (hand picking)
Sand and iron filings (using a magnet or panning)
Sand and salt (salt is soluble in water)
Sawdust and sand (density difference – sawdust floats in water or can be
blown away)
Sand and iron pyrites (panning)
Draw out from the discussion of the results the fact that in order to separate a
mixture, the components must have a difference in property, eg magnetic / non-
magnetic, soluble / insoluble, low density / high density etc.
The following lesson, the teacher demonstrates some separation methods actually
used to separate minerals.
Jigging
This method can be used to separate coal and rock waste on the basis of density.
The jigger described here is a small-scale model of a method used industrially.
Jigging is accomplished by filling the apparatus about one-fifth full of 2 to 5 mm coal /
'rock waste' mixture and plunging the jigger up and down in a bucket nearly full of