Question detail
For Purity, formulations and chromatography, which option uses the correct Chemical analysis evidence for pure substance?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Purity, formulations and chromatography
Question
- A. It raises the melting point
- B. It lowers the melting point
- C. It has no effect on the melting point
- D. It makes the melting point unpredictable
Answer
The correct answer is It lowers the melting point. It matches pure substance because the evidence is single element or compound / fixed melting point and the expected result is purity evidence.
Explanation
The correct option is It lowers the melting point. This response is stronger than the distractors because it keeps the test, observation, and interpretation in the correct order for pure substance. Other options are weaker when they confuse gas tests, flame colours, ion-test precipitates, chromatography evidence, or pure-substance/formulation wording.
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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