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Question

Difficulty: EasyDistinction Between Elements, Compounds, and Mixtures

A liquid sample collected from a reaction vessel is tested in a laboratory and observed to boil continuously over a temperature range of 102∘C102^\circ\text{C} to 106∘C106^\circ\text{C} at standard atmospheric pressure. Which classification of matter best describes this sample?

  1. A mixtureAnswer
  2. B
    A chemical compound
  3. C
    A pure element
  4. D
    A homogeneous pure substance

Answer

The correct answer is a mixture, because impure substances and mixtures boil over a range of temperatures rather than at a distinct, sharp boiling point.
A liquid that boils over a temperature range rather than at a single, fixed temperature is impure and constitutes a mixture. Pure substances (both elements and compounds) have definite compositions and sharp boiling points.

Step-by-Step Solution

1
Analyze the physical behavior described in the question.
The liquid boils across a temperature range of 102∘C102^\circ\text{C} to 106∘C106^\circ\text{C}.
Determining whether a substance has a sharp or broad boiling point is a key test of chemical purity.
2
Apply the criteria of purity for elements, compounds, and mixtures.
Pure elements and compounds have fixed compositions and fixed, sharp boiling points. Mixtures contain varying amounts of components and therefore boil over a temperature range.
The presence of multiple substances in variable proportions alters the vapor pressure continuously during boiling.

Key Concept

Distinction between pure substances (elements and compounds) which have sharp boiling points, and mixtures which boil over a range of temperatures.
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Topics

Distinction Between Elements, Compounds, and Mixtures