molar mass

[mohlam12]

Hey everyone,
I have this problem to solve:

A hydrocarbon (CxHy) contains 92.3% of Carbon and 7.7% of Hydrogen.
1) What is its molar mass, if the density of its smoke to the air is d=2.69 ?

92.3/7.7 = 12
So 12x=y
This is the first equation. I have to find a second one to find what is x and what is y, in order to find the molar mass of CxHy.

Is the density of water to the air can be written as d=(molar mass of the compound)/(molar mass of the water) ???

Anyhelp/hints would be appreciated.
Mohammed

[PPonte]

1) What is its molar mass, if the density of its smoke to the air is d=2.69 ?

Which are the units of this density, g/dm^3 ?

[Borek]

Sounds like it is ratio of its density (in gaseous form) to the air density.

"Molar mass" of the air is about 0.78*28+0.21*32+0.01*40 (ie air has density as if it was gas of this molar mass). Hydrocarbon molar mass is 2.69 times higher.

Best,
Borek
--
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[mohlam12]

Got It!! Thanks Everyone :)