Year 8 Science · Unit 3 · Lesson 15

Unit 3 Synthesis and Depth Study Preparation

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Learning Goals

Warm Up

Scenario

A student places 10 g of steel wool inside a sealed glass jar and records the mass of the jar + steel wool. Over the next week, the steel wool turns orange-red as it rusts. The student then records the mass again and finds it has increased to 10.43 g. She is puzzled: "How can the mass have increased if the jar was sealed and nothing went in or out?"

(a) Predict: Has conservation of mass been violated in this experiment? State your prediction.

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(b) Justify your prediction using the particle model of chemical change and the law of conservation of mass. Explain where the extra mass came from.

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Your Turn

Because… chain

Fill in the missing steps to trace the full pathway from investigation design through to writing a valid conclusion. Each step follows logically from the one before.

A student identifies their independent variable (acid concentration) and lists three controlled variables.
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The student runs three repeat trials at each concentration and records all results in a table.
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One result at 20% acid is much higher than the other two repeats and is flagged as a possible anomaly.
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After checking equipment and the anomaly cannot be explained by error, it is reported but excluded from the average.
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What a valid conclusion would include:

Show What You Know

1. A student investigating the reaction of bicarb and vinegar writes: "My experiment proved that more vinegar always makes faster reactions because my results showed this trend." Identify two weaknesses in this conclusion and write an improved version.

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2. Choose one natural system from Lesson 14 (e.g. weathering, carbon cycle, acid rain). Explain how the chemical changes in that system connect to conservation of mass and can be represented using a word equation.

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Wrap Up

In one sentence, what was the main idea of this lesson?

HSCScience · Year 8 Science · Unit 3 · Lesson 15 · Apply Worksheet