Multiple Choice
Which of the following are pure substances?
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1. Intro to General Chemistry
Classification of Matter
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Which of the following statements about air is true?
A
Air is a compound formed by the chemical combination of oxygen and nitrogen.
B
Air is a homogeneous mixture of gases.
C
Air is a heterogeneous mixture containing visible particles.
D
Air is a pure substance composed only of nitrogen.
Verified step by step guidance1
Understand the definitions of key terms: A compound is a substance formed when two or more elements chemically combine in fixed proportions, a pure substance has a uniform and definite composition, a homogeneous mixture has a uniform composition throughout, and a heterogeneous mixture has visibly different parts or phases.
Recall that air is primarily composed of nitrogen, oxygen, and other gases physically mixed together, not chemically bonded, so it is not a compound.
Recognize that air does not have visible particles or phases that can be distinguished by the naked eye, so it is not a heterogeneous mixture.
Note that air contains multiple gases, so it is not a pure substance composed only of nitrogen.
Conclude that air is best described as a homogeneous mixture of gases because its components are uniformly distributed and not chemically combined.
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