Taking the fearout of chemystery

12th May 1995 at 01:00
Changes of state and properties of materials may seem daunting subjects for the primary classroom, but Mick Revell shows there are many suitable and enjoyable activities. Materials and their properties, the title of the third attainment target in science, may not sound intimidating but to teachers without a science background it can recall uncomfortable memories of lessons in their youth which seemed more "chemystery" than chemistry.

Yet all five to 16-year-old children in England and Wales should study materials and their properties and at key stages 1 and 2 they may well be taught by teachers who feel hesitant about the topic.

The programmes of study at KS12 provide valuable learning about the nature of materials that lays foundations for important aspects of chemistry education later on. Most of this can be achieved in infant and junior classes through a variety of simple activities using everyday materials found in most primary schools. Less available is a widespread bank of ideas for activities. The recently published Chemistry and Cookery provides primary teachers with a range of ideas for use in class, and the background information needed to feel more in command of the subject matter.

The Dearing review has slimmed the contents of this attainment target. The removal of ideas about rusting and burning as a chemical reaction with oxygen will be mourned by few, although much of the enjoyable work with chromatography, and using indicators to sort acids and alkalis, may be retained in many primary classrooms despite its disappearance from the core programme of study. Ideas of dissolving, mixtures and separation have been among those most successfully encompassed in primary science, but two areas of attainment target 3 that primary teachers have found more difficult to introduce into the classroom are solids, liquids and gases, and chemical changes. Both these areas have been retained in the Order following the Dearing review; fortunately there are a many explorations and investigations which children and teachers can enjoy.

Solids, liquids and gases Feely bags can turn learning about the properties of solids, liquids and gases into a hands-on experience. A partially inflated balloon, a wooden block and a polythene bag filled with water provide simple tactile experience of their properties. They can be double-wrapped in polythene bags for protection and to stimulate language work describing properties and sensations while the objects remain unseen.

Grouping objects into the three categories is a useful activity but the lack of readily available gases for children to "see" or "handle" is a limitation. Card-sort activities, matching games, snap, Pelmanism, etc offer a partial solution. To extend children's limited experience of gases it may be helpful to include examples such as wind, candle flame, car exhaust fumes, steam, camping and lighter gas, the gas argon, which fills light bulbs, and helium or hydrogen-filled balloons. Although some of these examples could only be loosely termed gases, they will help children develop their concept of a gas at this stage. Fitting a polythene bag over the neck of a bottle of fizzy drink will help children see the carbon dioxide bubbles in the drink as an example of a gas.

Although the following are oversimplified and idealised descriptions they will be enough for many children at this stage and the anomalies form the basis of fruitful discussion. Some typical properties, expressed in terms appropriate to KS2, are: o Solid hard; heavy; stays still (unless pushed); fixed shape; doesn't squash o Liquid soft; heavy; runny; no fixed shape; doesn't squash; transparent o Gas soft; light; floats; no fixed shape; can be squashed; invisible.

Having to describe the characteristics of solids, liquids and gases will help children develop their concepts of a material and its properties as distinct from the artefact and its characteristics.

Three sandwich bags, one inflated with air, one filled with water and one filed with plaster of Paris which is poured and allowed to set, will provide children with a simple and surprisingly effective stimulus for establishing typical properties of solids, liquids and gases. Working with runny solids such as sand, and other non-standard examples such as modelling dough, shower gel and treacle can help extend discussion to more subtle differences.

Children find it difficult to differentiate between materials that are pliable and materials that may be compressed. The shape of water or modelling dough can be changed but their volume remains constant: they are not compressed. A plastic 20ml syringe, the end of which has been sealed by the teacher by melting it in a match flame, is a simple tool for exploring compressibility. Such syringes filled with modelling dough, water and air will enable children to explore how a gas can be compressed but liquids and solids cannot. The kind of ice lollies that come sealed in polythene tubes for making in the home freezer are another homely yet invaluable aid for learning about solids and liquids. They can be changed backwards and forwards many times and the changing properties observed, yet their convenient container enables their constant mass to be established by using kitchen scales.

Chemical changes Children need to learn to distinguish between physical change and chemical change, and later from this idea of chemical change to develop an understanding of chemical reactions. It can sometimes be difficult to distinguish precisely between physical and chemical change. However, at this level it is usually adequate to regard a physical change as one in which no new substance is formed and that can be easily reversed. Chemical change should be regarded as a more profound change in the material, hard to reverse and one in which a new substance is formed.

Children can explore many physical changes besides freezing and melting. Straightforward examples are dissolving salt in water and reclaiming it by evaporation on the window sill; straining rice from water; filtering muddy water; sieving soil; drying wet clothes. All are easily reversed.

At first sight the study of chemical changes might appear too difficult for the typical primary classroom but there are a number of suitable activities linked with cooking. The changes that occur when potatoes are cooked, bread toasted, eggs boiled, bread, biscuits or cakes baked, are familiar examples of chemical change which can be exploited as learning opportunities. Contrasting the physical changes that occur as the ingredients are mixed with the permanent change as they are cooked will help emphasise differences between physical and chemical change. Comparing the changes that happen when no-cook cheesecake mix is made by one group with the more profound chemical change when a cake is baked by another group will help clarify differences between physical and chemical changes.

Yoghurt-making is a chemical-change activity. Results are usually more vivid if it can be left overnight. Baking egg custard lends itself to identifying and controlling some of the factors in the investigation: ingredients, oven temperature, cooking time, firmness of the cooked custard. The nature of the chemical change is evident through changes in the texture, colour, smell, taste and appearance of the custard.

Besides cooking, other practicable examples of chemical change can be investigated, for example, the rusting of wet nails, the browning of a cut apple and the burning of a night-light candle. Schools with access to a pottery kiln should use it to illustrate chemical changes. The differences between moist clay and fired pottery are a striking example of the formation of a new substance. It is helpful to make small clay bricks and to air some slowly over a radiator and to fire others in the kiln. The dried clay can be moistened and softened again - physical change - in contrast to the irreversible change of the fired clay.

When plaster of Paris is set in a thin disposable cup the release of heat during the chemical reaction is detectable by touch. Persistent investigators can crush up the finished plaster and try to re-use it, to establish that the change is not easily reversed. Effervescent indigestion tablets are a convenient material for studying chemical change, for example by making a fizz bomb. The standard size of each tablet leads itself to quantitative investigation.

Sherbert is a fun material. The ingredients are icing sugar, bicarbonate of soda and citric acid, all easy to buy. Adding water causes a chemical reaction in which bubbles of carbon dioxide are released, the familiar fizz. Children can investigate which combination of ingredients is needed to make it do this. It provides everything for a challenging investigation involving identifying the relevant factors, planning, obtaining evidence, evaluating the reliability of the evidence, drawing a conclusion and explaining.

o Chemistry and Cookery is available from NIAS, Northamptonshire Science Centre, Lewis Road, Northampton, NN5 7BJ .Tel: 01604 756134. Pounds 12 + Pounds 2 pp. The chemistry and cookery project is supported by Glaxo Wellcome Mick Revell is head of Northamptonshire Science Centre, Northamptonshire Inspection and Advisory Service

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