Samples of 14 g of N₂(g) and 16 g of CH₄(g) are mixed in a rigid container at 298 K

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

Problem

Samples of 14 g of N₂(g) and 16 g of CH₄(g) are mixed in a rigid container at 298 K. Which statement best describes the average molar mass of the resulting gaseous mixture? (a) About

22\,\text{g mol}^{-1}

, the simple arithmetic mean of

16

and

28\,\text{g mol}^{-1}

. (b) Exactly

16\,\text{g mol}^{-1}

since the lighter gas dominates the mixture. (c) Approximately

20\,\text{g mol}^{-1}

; it lies between

16

and

28\,\text{g mol}^{-1}

and is closer to

16\,\text{g mol}^{-1}

because the mixture contains twice as many moles of

\mathrm{CH_4}

as of

\mathrm{N_2}

. (d) Nearly

24\,\text{g mol}^{-1}

after (incorrectly) weighting the two molar masses by their gram amounts rather than by their mole amounts.

Related theory

Mole concept
Some Basic Concepts of Chemistry
Mole and mass
Mole Concept and Molar Masses

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