This is distinct from other changes such as evaporation, melting, boiling, freezing and mixing where changes involve no new substances. The properties of the new materials are different from those of the reactants. Chemical reactions involve interaction between chemicals such that all reactants are changed into new materials. Scientific viewĪll materials are made of chemicals. Hence students may regard chemicals as a group of substances found in laboratories rather than seeing all the substances in foods (for example) as chemicals.
In everyday language, the word ‘chemical’ is often used as a label for undesirable things that shouldn't be in foods or cosmetics. Research: Arizona State University (2001)īecause so many reactions children know about are involved in things like cooking and burning, they assume that heat is always necessary for reactions to occur. In burning carbon based materials such as wood, students believe that charcoal (carbon) appears from the In their view, air has little to do with burning. In combustion, children frequently believe materials like wood or paper just disappear - after all there is not much of the product left to see. Processes like cordial mixing with water, the use of colouring in food, freezing and boiling are seen as similar to chemical changes like those involved in cooking eggs. Gas bubbles that are frequently produced when a tablet dissolves in water are often not seen by students as a new substance. Similarly, rust flaking off is usually not noticed – it is thought that the iron just disappears. For example, students consider that rust is still iron/steel it has just gone brown. When a chemical reaction does take place, they believe that one or other of the reactants is simply modified it hasn't really changed. Students frequently believe that to get something new, things just need to be mixed together.
Yet an understanding of chemical change is fundamental to appreciating the role of chemistry in their lives and at this level students can begin to appreciate this. Because students rarely understand the concept of ‘a substance’ they don't see substances being changed. For example they see smoke as part of the wood that is somehow released when the wood burns. However at this level students don't see new materials being produced as a result of chemical change, rather they see that existing materials have merely been modified in some way. They are familiar with burning, cooking, rusting and chemical processes that appear to involve dissolving. Contrasting student and scientific viewsĬontrasting student and scientific views Student everyday experiencesĬhildren will have experienced many examples of chemical change without actually realising it.
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