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Assuming that air contains 78 percent N2,21 percent O2,
Chapter 5, Problem 46P(choose chapter or problem)
Assuming that air contains 78 percent \(\mathrm{N}_{2}, 21\) percent \(\mathrm{O}_{2}\), and 1 percent Ar, all by volume, how many molecules of each type of gas are present in 1.0 L of air at STP?
Questions & Answers
QUESTION:
Assuming that air contains 78 percent \(\mathrm{N}_{2}, 21\) percent \(\mathrm{O}_{2}\), and 1 percent Ar, all by volume, how many molecules of each type of gas are present in 1.0 L of air at STP?
ANSWER:Step 1 of 2
The goal of the problem is to find the number of molecules of each type of gas that are present in \(1.0 \mathrm{~L}\) of air at STP.
Given:
Volume \(=1.0 \mathrm{~L}\)
Mass of \(\mathrm{N}_{2}=78 \%=(78 / 100)=0.78\)
Mass of \(\left.\mathrm{O}_{2}=21 \%=21 / 100\right)=0.21\)
Mass of \(A r=1 \%=(1 / 100)=0.01\)
STP is nothing but Standard Temperature and Pressure. The standard temperature is \(273 \mathrm{Kand}\) the standard pressure is 1 atm pressure.
First, let's find the number of particles in the air:
We know, at STP, 1 mole of any gas contains \(22.41 \mathrm{~L}\) of particles. Therefore
\(\begin{aligned} \text { Number of particles }= 1.0 \mathrm{~L} \times \frac{1 \mathrm{~mol}}{22.41 L} \times 6.023 \times 10^{23} / \mathrm{mol} \\ =2.68 \times 10^{22} \text { particles. } \end{aligned}\)