Density of air at one atmosphere pressure

[Bolter]

Homework Statement

Calculate the density of air

Relevant Equations

PV = nRT

How would I tackle a problem like this?

I made a start by writing down the ideal gas equation and then done some manipulation on both sides to get the density expression of the ideal gas.
I'm not sure if this is what the question wants as I'm dealing with 2 different types of gases in the same atmosphere.
My density formula that I have obtained only applies to find the density of one type of gas?

Also is there a typo in the question itself? Should it read "Determine the density of air at 25 degrees at one atmosphere pressure" instead of "Determine the density of air at 25 degrees and one atmosphere pressure"?

Any help would be grateful!

 

[BvU]

Hello again !

We recommend you learn some $\LaTeX$ to post formulas. It's compact, fairly easy:
$$ pv = nRT $$ becomes $$pV = nRT$$ and ## d = \frac {pM_m}{RT} ## becomes $d = \frac {pM_m}{RT}$

SInce $M_m$ (the molar mass) is different for each gas: yes, as written yuor expression works for single-composnent gases. For mixtures you need a mixing rule. FOr that you need to know whether the percentages given are by volume or by mass ...
A little googling establishes that the percentages are mol based, i.e. volume.
So the mixing rule is pretty straightforward, right ?

And you can always check the result with that same search engine...

Also is there a typo in the question itself?

No typo: the text sums up the conditions, so the word 'and' is appropriate.

 

[Bolter]

Hello again !

We recommend you learn some $\LaTeX$ to post formulas. It's compact, fairly easy:
$$ pv = nRT $$ becomes $$pV = nRT$$ and ## d = \frac {pM_m}{RT} ## becomes $d = \frac {pM_m}{RT}$

SInce $M_m$ (the molar mass) is different for each gas: yes, as written yuor expression works for single-composnent gases. For mixtures you need a mixing rule. FOr that you need to know whether the percentages given are by volume or by mass ...
A little googling establishes that the percentages are mol based, i.e. volume.
So the mixing rule is pretty straightforward, right ?

And you can always check the result with that same search engine...

No typo: the text sums up the conditions, so the word 'and' is appropriate.

Are you suggesting that I work out the average molar mass of the mixture? So to do that I take the sum of the mole fractions of each gas multiplied by the molar mass of that gas.
And from that, I substitute that average molar mass value into the density expression that I got prior.

And thanks I will definitely have a look into the LaTex guide page so I can start using them on the threads

 

[BvU]

Seems a bit heavy to me ...