[DulceBoxers]

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A mixture of Ar and N2 gases has a density of 1.413 g/L at STP. What is the mole fraction of argon gas?
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                                  Moles of Component
MOLE FRACTION (X) = ----------------------------
                                  Total Moles in Mixture  

Without any emphasis on the amounts of Ar and N2 in the mixture, I dont know how to go about finding how many moles of Ar are in this mixture, or even how many moles the mixture contains. Any help would be EXTREMELY appreciated, hopefully Im just missing something very obvious.

-There is NO MORE info to the question, and no charts or any type of referrels at all.e

[Borek]

What is molar mass of the Ar?
What is molar volume of Ar at STP?
What is Ar density at STP?

Same questions for N₂.

Imagine mixture of x mole Ar (x < 1) and 1-x mole N₂.

What will be the volume of such mixture at STP?
What will be its mass?
What will be density?

Now reverse the calculations.

[DulceBoxers]

What is molar mass of the Ar? 40g
What is molar volume of Ar at STP? 22.414 L
What is Ar density at STP? 1.785 g/L

Same questions for N₂.
28 g
44.828 L
2.50 g/L

Imagine mixture of x mole Ar (x < 1) and 1-x mole N₂.

What will be the volume of such mixture at STP? 22.414 L
What will be its mass?
                                  > Not sure where to start
What will be density?

Now reverse the calculations.

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Okay so from here Im going to go to my notebook and try to solve with the general layout you wrote. What is confusing me most is the lack of specifications of the actual molecule.

Thank you for the time! Ill write back when on my progress.

[DulceBoxers]

I have a system of equations that might work:

xAr + (1-x)N₂=1
x1.785g/L + (1-x)2.5g/L = 1.413g/L (Ar and N2 densitites equalling the resultant density)

Do these make sense ?

[Borek]

Several mistakes:

1. Why do you think volume of N₂ mole will be 44L?

2. Where did you get 2.5 g/L (shown as density of N₂) from?

3. Equation you proposed doesn't form a set - first one is always true, regardless of x value.

4. Second equation is wrong, but you are trying to go in the right direction. Try again. Calculate mass of mole of mixture for given x.

[DulceBoxers]

Several mistakes:

1. Why do you think volume of N₂ mole will be 44L? now I believe now it is 22.414L. I was thinking that N₂ would constitute 2 moles of gas.

2. Where did you get 2.5 g/L (shown as density of N₂) from?now I believe it is 1.25 g/L . I got 2.5 from a logical mistake.

3. Equation you proposed doesn't form a set - first one is always true, regardless of x value.

4. Second equation is wrong, but you are trying to go in the right direction. Try again. Calculate mass of mole of mixture for given x. Okay, I'll post my progress[/Red]

[DulceBoxers]

Calculate mass of mole of mixture for given x.

Mass of 1 mole of mixture, given x =

40x + 28(1-x);

And since density of mixture = 1.413 g / L,

and there are 22.414 L in 1 mole,

then mass of one mole of mixture would be

22.414 L          1.413 g
-----------  X  ----------    = 31.67 g / mol;
    mol               1 L  

so going back to the molar mass with value of x,

40x - 28x + 28 = 31.67
12x = 3.67
x = .306 mol


Molar mass of Ar =   .306 mol / 1 mol



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THE SYSTEM HAS AN AWNSER OF .3064 +/-  5%

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THANK YOU Borek!!!! You led me in a very straight direction and i appreciate it. Now, to understand how this works!