3.2 To investigate and discuss physical and chemical changes in

Natural sciences

Matter, measuring and reactions

Educator section

Memorandum

Examples of physical change: a pan that is heated; tea that cools down

Examples of chemical change: burning match; toasting bread

Marshmallow

• Yes, it tastes slightly different after being toasted
• Yes, it became black and powdery
• Chemical change. It is permanent - the chemical reaction changed the sugar to carbon.

Leaner Section

Content

Activity: to investigate and discuss physical and chemical changes in substances [lo 2.3]

People make use of different natural substances and change them into something else. To achieve this change, substances are mixed with other substances, heated, separated, dissolved or treated with electricity. Some changes are not permanent, while other changes cannot be reversed. We also distinguish between physical and chemical changes.

Physical Change

When crystallised honey is heated in a pot it becomes fluid again. But when it cools down and is exposed to air, it will crystallise once more. No new substances are formed and the properties of the honey remain exactly what they were. The change is a physical change. In the previous experiment, the orange/red mercuric oxide became black when it cooled down (physical change).

Chemical change

When you pour pancake batter into warm oil, something happens: the appearance of the batter changes. It is not runny any more, but stiff. The change that occurs is permanent. A change that is permanent and results in something new is a chemical change. The properties of the new substance differ from those of the original substances. The mercuric oxide also experienced a chemical change when it was decompounded into mercury and oxygen.

Name two further examples of physical and two examples of chemical change:

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Try the following:

Bring some marshmallows to school. Push them onto the prongs of a fork and heat them over a flame. Answer the questions that follow.

• Taste a marshmallow (when it has cooled down). Has the taste changed?
• Has the appearance changed? Describe what you observe.
• Did this involve a physical or a chemical change? Motivate your findings.

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Assessment

Learning Outcome 2: The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

Assessment Standard 2.3: We know this when the learner interprets information by identifying key ideas in text, finding patterns in recorded data, and making inferences from information in various forms (e.g. pictures, diagrams, text).