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. Click on the link below and read about this incident before working the problem below. http://en.wikipedia.org/wiki/Lake_nyos

1. Determine the weighted average for the molar mass of dry air assuming the approximate compositions below.

N2 , 78%, O2, 21%, Ar, 1%

2. 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., 18C.

3. Calculate the density of carbon dioxide gas using the d = PM/RT equation. Assume the same conditions as specified in #2 above.

4. Use your results from above to answer the questions below. a. Which beaker would represent the flow of CO2 gas when the two beakers containing dry ice are left open to the environment, beaker A or beaker B?

Explain . b. Are your results from questions 2 and 3 consistent with what happened at Lake Nyos? Yes or No/Explain.

Explanation / Answer

Basis : 1 mole of air and . It contains 78%N2, 21% O2 and 1%Ar.

Moles : N2=0.78, O2=0.21 and Ar=0.01

Molar mases : N2=28, O2=32 and Ar =40

Mases (gm) : N2= 0.78*28 =21.84 , O2= 0.21*32 =6.72 and Ar= 0.01*40=0.4

tota mass = 21.84+6.72+0.4=28.96 gm

mass percetnage : 100* mass/total mass

Mass percentages : N2= 100*21.84/28.96=75.41%, O2= 100*6.72/28.96= 23.2% and Ar= 100*0.4/28.96=1.38%

for one mole, mass = molar/mass = 28.96

2. d= PM/RT =1*28.96/(0.0821L.atm/mole.K)*(18+273.15) =1.2131 g/L = 1.211 kg/m3

3. For CO2, molar mass =44 and density = 1*44/(0.0821*291.15) = 1.84 g/L= 1.84 kg/m3

4. Both beakers flow of CO2 since both are filled with dry ice.

air is less dense than CO2 and hence rises up. Hence the movement CO2 escapes,   air moves up.

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