A tragedy occurred at Lake Nyos in Cameroon (Africa) during the summer of 1986 .

Question

A tragedy occurred at Lake Nyos in Cameroon (Africa) during the summer of 1986 . During the process of unraveling this mystery scientists had to rely on basic concepts of gas behavior which they most likely learned in a general chemistry class. Moreover, the PV=nRT equation was an especially important tool used by the scientists to help determine what happened in
this tragedy.

Determine the weighted average for the molar mass of dry air assuming the approximate
compositions below.
N2 , 78%, O2, 21%, Ar, 1% and Calculate the density of dry air using the result from above and the d = PM/RT equation......Assume the overnight conditions during this tragedy were as follows: pressure , 1 atm and the temp., 18 C. Calculate the density of carbon dioxide gas using the d = PM/RT equation.

Explanation / Answer

MW of N2 = 28g/gmol

MW of O2 = 32 g/gmol

MW of AR = 39.9 g/gmol

MW overall = 0.78*28 + 32*0.21 + 0.01*39.9 = 28.96 g/gmol of air

MW of dry air =28.96 g/gmol

Density

PV = nRT

C = n/V = P/RT

We need to change moles to mass with MW D = C/MW

D = P*MW / (RT)

D = 1*28.96/ (0.082*291) = 1.2136 kg/m3

D = 1.2136 kg/m3

NOW

for CO2

MW = 44

D =P* MW/(RT) = 1*44/(0.082*291) = 1.8439 kg/m3 of CO2

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