A student claims that a sample of and a sample of contain the same number of…

CHEMISTRY · Single correct · AP · Chemistry · Atomic Structure and Properties · Atomic Structure and Properties

Problem

A student claims that a

32\,\text{g}

sample of

\text{O}_2

and a

32\,\text{g}

sample of

\text{CH}_4

contain the same number of molecules because their masses are equal. Which of the following best evaluates the student’s claim? (a) The claim would be correct only if both gas samples occupied the same volume at the same temperature and pressure, because equal volumes of gas under identical conditions contain equal numbers of molecules. (b) The claim is incorrect because the substances have different molar masses, so equal masses do not correspond to equal numbers of molecules. (c) The claim is correct because

32\,\text{g}

corresponds to

2\,\text{mol}

of each substance, so the samples contain the same number of molecules. (d) The claim is correct because mass is directly proportional to the number of molecules, regardless of substance identity.

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