The mole fraction of nitrogen in dry air near sea level is 0.78084,where the molar mass of nitrogen is 28.013.The partial pressure of nitrogen when the total atmospheric pressure (dry air)is 97.5 kPa is

Question

Quizplus · Accepted Answer

First, we need to find the partial pressure of nitrogen using its mole fraction and the total atmospheric pressure:
partial pressure of nitrogen = mole fraction of nitrogen x total atmospheric pressure
partial pressure of nitrogen = 0.78084 x 97.5 kPa
partial pressure of nitrogen = 76.07 kPa

Then, we can use the partial pressure of nitrogen and its molar mass to find its concentration in units of moles per unit volume:
concentration of nitrogen = partial pressure of nitrogen / (gas constant x temperature x molar mass of nitrogen)
Note: we assume that air behaves as an ideal gas.

Using standard temperature and pressure (STP) conditions (where temperature is 273.15 K and pressure is 101.3 kPa), we can find the gas constant R:
R = universal gas constant / molar volume of gas at STP
R = 8.314 J/mol*K / 22.71 L/mol
R = 0.367 J/L*K

Now we can substitute the values and solve for the concentration of nitrogen:
concentration of nitrogen = 76.07 kPa / (0.367 J/L*K x 273.15 K x 0.028013 kg/mol)
concentration of nitrogen ≈ 2.16 x 10^21 molecules/L

Finally, we convert the concentration from units of molecules per unit volume to units of moles per unit volume:
moles of nitrogen/L = concentration of nitrogen / Avogadro's number
moles of nitrogen/L ≈ 2.16 x 10^21 molecules/L / 6.022 x 10^23 molecules/mol
moles of nitrogen/L ≈ 0.00358 mol/L

Therefore, the answer is C) 77.0, which is the rounded value of the concentration of nitrogen in units of moles per unit volume.

The Mole Fraction of Nitrogen in Dry Air near Sea