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Difficulty: EasyPure and Impure Substances and Criteria of Purity

Which of the following physical properties best confirms that a solid chemical sample is pure?

  1. It melts completely at a sharp, fixed temperature.Answer
  2. B
    It melts gradually over a wide range of temperatures.
  3. C
    It boils over a broad temperature interval above its normal boiling point.
  4. D
    It forms two separate spots when developed on a paper chromatogram.

Answer

It melts completely at a sharp, fixed temperature.
Pure solid compounds melt at a fixed, sharp temperature characteristic of that substance. A sharp melting point is a definitive physical criterion of purity for crystalline solids.

Step-by-Step Solution

1
Identify the standard criteria of purity for a solid substance.
A pure solid possesses a sharp and definite melting point.
Soluble impurities disrupt the uniform crystal lattice of a solid, depressing its melting point and causing it to melt over a broad temperature range.

Key Concept

Criteria of purity for solid substances
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Topics

Pure and Impure Substances and Criteria of Purity