[gyromag]

Greetings,

I am having difficulty with calculating the mol ratio of argon (MW 39.95) to nitrogen (28.01) if the calculated MW is 28.15.  This problem is taken from Zumdahl's Chemical Principals 2nd Ed. (Chapter 5 #29) and the answer is given at the back of the book as 1.18 X 10^-2.  Can someone nudge me in the right direction on how to arrive at this response?  Thanks!

[Borek]

Try with molar fractions.

Assuming there is x of one and (1-x) of another, calculated molar mass is 39.95x + (1-x)*28.01.

[tennis freak]

to do this wouldnt you need to know how many moles of each there were in the reaction? and where does that mass come from anyway?

[Borek]

There is no reaction here, there is a mixture of two gases that behaves like gas of given molar mass.

[Donaldson Tan]

let mol% of Argon be x

=> mole% of Nitrogen = 1 - x

Average Molar Mass = x*(molar mass of Argon) + (1-x)*(molar mass of N₂)

Solve for x