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Which of the following best describes the water table in the context of the classification of matter?
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1. Intro to General Chemistry
Classification of Matter
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Which of the following is good evidence that an unknown sample is a pure substance?
A
It dissolves in water to form a cloudy mixture.
B
It has a constant melting point.
C
Its color changes when exposed to air.
D
It can be separated into two components by filtration.
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Understand the definition of a pure substance: a material that has a fixed composition and distinct properties, such as a constant melting point.
Recognize that a constant melting point is a key physical property of a pure substance because impurities typically cause melting point depression and broadening.
Analyze the other options: dissolving to form a cloudy mixture suggests a suspension or mixture, not purity; color change upon exposure to air indicates a chemical reaction or instability, not purity; separation by filtration implies the sample is a mixture, not a pure substance.
Conclude that the presence of a constant melting point is strong evidence that the sample is a pure substance because it reflects uniform composition and consistent physical behavior.
Therefore, the correct evidence for purity is that the sample has a constant melting point.
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