Question detail
In the kestrel written-response scenario for Pure substances, explain how pure substance chromatography supports this objective: Use melting point data to identify a pure substance..
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Question
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exam_style
Style
Topic
Purity, formulations and chromatography
Question
In the kestrel written-response scenario for Pure substances, explain how pure substance chromatography supports this objective: Use melting point data to identify a pure substance..
Answer
A high-scoring answer should explain use melting point data to identify a pure substance. Use evidence before identification: name the relevant test or measurement, state the observation, and then connect the result to Pure substances.
Explanation
The important distinction is that pure substance must be identified from single element or compound / fixed melting point; answers that swap in a different test or result do not match Pure substances. A complete answer should use the approved objective wording, include the relevant evidence, and avoid unsupported identification claims.
Common mistake
Misinterpreting a narrow melting range
Students often think a substance with a slightly broadened melting range is still pure, assuming the range is just experimental error.
Explain that a pure substance should have a sharp, narrow melting point range (typically 1–2 °C). A broadened range indicates the presence of impurities, which lower and broaden the melting point. Therefore, a substance with a noticeably wider range should be considered impure, not pure.
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