partial pressure calculation....

[Smooth Operater]

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if the partial pressure of carbon dioxide is 30 torr at STP, the gas is 10 % carbon dioxide by mass, and there is only on other species of gas present, which of following could be the other species of gas?

A. hydrogen
B. Methan
C. Oxygen
D. Chlorine

the answer is Methan. But how would you get it by calculation? Thanks!

 

[Smooth Operater]

bump

 

[dudewhensmydat]

Wow! I dunno. This is a neat question. I was trying to use PV=(m/MM)RT and partial pressure equation, but nothing was happening.

I'll try again tomorrow morning.🙄

 

[Smooth Operater]

yea, same here, i am working on it. if anyoe knows, plz post. 😀

 

[doc toothache]

Since we are dealing with conditions at STP, the unknown gas must be exerting 760-30=730 torr.

partial pressure of gas= (mole fraction of gas) (pressure of pure gas)
(STP for pure gas would be 760)

730=(mole fraction of unknown gas) (760)
730/760=0.96=mole fraction of unknown gas

The conditions given are of mass. Assume 100g total mass of gas. Then

moles of CO2= 10/44=0.23

moles of unknown gas= 90/mol. wgt of unknown gas (set =M)

mole fraction of unknown gas= M/(M+0.23),
0.96=M/(M+0.23) calculating for M
M = 5.45
M = 5.45 = 90/mol wgt unknown gas
mol. wgt unknown gas = 16.3