Question

4. The atmosphere is composed of about 78% nitrogen, 21% oxygen, and 1% argon. Typical atmospheric pressure in Boulder, Colorado is about 0.83 atm. What is the pressure contributed by each gas?​

Answer 1

ANS

Step 1 :Explanation of required formula.

According to Dalton's Law of Partial Pressures, the partial pressure of a component of a gaseous mixture depends on the mole ratio of said component and the total pressure of the gaseous mixture

i.e Pi=Xi × Ptotal,

Here we don't know exactly how many moles of the mixture we have,

but we know that 78.0% of all the molecules present in the mixture are nitrogen molecules, 21.0% are oxygen molecules, and 1% are molecules of Ar gas.

As we know, a mole is simply a very large collection of molecules. In order to have one mole of a substance, we need to have 6.022 × 1023 molecules of that substance.

This means that the actual number of moles is not important here, because the ratio that exists between the number of molecules is equivalent to the ratio that exists between the number of moles.

Hence,

Step 2 : Calculate of mole fraction of the mixture.

mole fraction of nitrogen = 78 /100 = 0.78

mole fraction of O2 =

21 /100 = 0.21

mole fraction of Argon =

1 /100 = 0.01.

Step 3 : Calculate the pressure contributed by each of the mixture.

The pressure contributed by N2 = mole fraction of N2 × Total pressure = 0.78 × 0.83 atm = 0.6474 atm

The pressure contributed by O2 = 0.21 × 0.83 atm = 0.1743 atm

The pressure contributed by N2 = 0.01 × 0.83 atm = 0.0083 atm.

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