The estimated average concentration of NO2 in air in the United States in 2006 w

Question

The estimated average concentration of NO2 in air in the United States in 2006 was 0.016 ppm.

Only need the answer to part B!

Part A

Calculate the partial pressure of the NO2 in a sample of this air when the atmospheric pressure is 747 torr (99.6 kPa ).

Express your answer using two significant figures.

1.2×105

  torr

Part B

How many molecules of NO2 are present under these conditions at 24 C in a room that measures 17 × 16 × 9 ft ?

Express your answer using two significant figures.

1.2×105

  torr

Explanation / Answer

The average concentration of NO2 is 0.016
So it means 0.016 mole per 10^6 mol
Thus the fraction is 1.6*10^-8
The atmospheric pressure 747 torr
The partial pressure of NO2 is calculated as follows:
PNO2= XNO2*Patm
=1.6*10^-8*747
=1.19*10^-5 torr
--------------------------------------------------------------------
b) Ideal gas equation is as follows-
PV=nRT
n=PV/RT
Here,
P=1.19*10^-5 torr*1atm/760 torr= 1.56*10^-8 atm

V=17 × 16 × 9 ft = 2448 ft^3*28.3168L/1ft^3= 69319.53 L
R=0.08201 L atm mol^-1 K-1
T= 24 oC=297 K
Thus
n= 1.56*10^-8 atm *69319.53 L/(0.08201 L atm mol^-1K^-1*297 K)

=4.44*10^-5 mol
The number of molecules can be calculated as shown below
4.44*10^-5 mol*(6.023*10^23 molecules/mol=2.67*10^19 molecules

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