Separate physical and chemical changes

Supplied materials

• All measurements and observations below are supplied classroom examples. They are not data from actual learners or a claim about a particular real site.
• Paper or a browser document for a labeled drawing, table or explanation.
• Worked problem inputs: A clear unknown liquid bubbles. Give two scientifically distinct explanations and the missing evidence.
• Assessment case 1: Pure water freezes and product identity remains H₂O. What is warranted? Which inference or prediction is best supported?
• Assessment case 2: Which transformation category is supported by the supplied identity information? Supplied case: Record confirms iron oxide forms.
• Assessment case 3: Which evidence category describes the observation or chemical analysis? Supplied case: Unknown liquid bubbles without product analysis.
• Assessment case 4: Which evidence category describes the observation or chemical analysis? Supplied case: Analysis identifies a new compound.
• Assessment case 5: Which transformation category is supported by the supplied identity information? Supplied case: Salt dissolves without identity change.
• Assessment case 6: Analysis identifies new chemical products after a model process. What conclusion is stronger than bubbles alone? Which inference or prediction is best supported?

Learn the idea

A physical change can alter state or arrangement without changing chemical identity. A chemical reaction forms different substances. Color or bubbling alone may be suggestive but is not always conclusive.

Physical change means identity retained while form changes. Chemical change means new chemical substances form. Suggestive observation means may indicate reaction but has alternatives. Identity evidence means record identifies products chemically.

For the supplied mechanism problem, A clear unknown liquid bubbles. Give two scientifically distinct explanations and the missing evidence. Gas could form in a chemical reaction or leave solution without new chemical identity. Bubbling alone does not decide. Product identity or additional suitable measurements are needed.

1. Read the supplied problem and mark the structures, processes or quantities named: A clear unknown liquid bubbles. Give two scientifically distinct explanations and the missing evidence.
2. Draw the relevant boundary, pathway or comparison and label it using the scientific ideas above.
3. Write a causal explanation or calculation, showing how each observation supports the result.
4. Compare your reasoning with the worked solution; name a condition that would change or limit the inference.

Check your reasoning

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Take it further

New case: ice becomes water and a second record chemically identifies a new oxide from a metal. Expected: first is a state change retaining identity; second is chemical change. A visible change alone is not the deciding evidence.

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