Question

If the only given information of a question is the density, temperature and pressure of a mixture of oxygen and krypton, how would you find the mole percentage of krypton?

Answer 1

Well, I only got up to finding the molar mass of the mixture:
using MM=dRT/P

Answer 2

I do not remember the exact numbers of each given information, I only recalls getting 51.33g for the molar mass of the mixture.

Answer 3

So the density, temp, and pressure are all for the mixture?

Answer 4

yes

Answer 5

Not separate?

Answer 6

@yociyoci
Did the question provide density or vapour density ??

Answer 7

density

Answer 8

You already found the molar mass of the mixture.

Assume the ration of moles of oxygen and krypton = x:1

Answer 9

This will give you an equation -
(molar mass of oxygen)x + (molar mass of krypton) = molar mass of mixture

I think, the rest would be obvious :)

Answer 10

@yociyoci Does that ^^ helps ??

Answer 11

Umm.... I don't really understand...

Answer 12

Oops..my equation was terribly wrong :'(

Answer 13

Consider this -
Molar mass of a sample
= (total mass) / (total number of moles)
= (16x + 83.8) / (x + 1)

It ^^ is analogous to the "center of mass" concept of physics XD

Answer 14

(32.0x+83.8)/(x+1) ?

Answer 15

Yea..32 (I forgot it is O2)

Answer 16

MM=(32.0x+83.8)/(x+1)
51.33g=(32.0x+83.8)/(x+1)
51.33x+51.33=32.0x+83.3
19.33x=32.47
x=1.68 mol O2

Answer 17

What would be the next step?

Answer 18

'x' is just a ratio of moles of O2 : moles of Kr

You can use it to find the mole fraction or mole percentage..try yourself and I'll check it :)

Answer 19

1.68 mol O2 : 1 mol Kr
1/(1.68+1) x 100%= 37.3% Kr

Answer 20

:)

Answer 21

Thank you!!! Thanks for helping me figure this out~ =D

Answer 22

You should also thank @wolfe8 for staying on OS 24/7
I always check his last few posts to find who needs help.. :D

Answer 23

Huh? I barely helped today. I went out.

Answer 24

You at-least filter out those who need help from those who just want an answer (and of-course those who simply don't bother to close their question)

Answer 25

Thanks to both of you guys!! I really appreciate you guys staying with me for this hour to work this out! Especially @wolfe8 for helping me with chemistry these couple for days! Last night, we spent hours trying to figure out a solution, although it's very late, he stayed with me until I figured out the problem!!!

Answer 26

I really appreciate this!! Thank you so much~ =D

Answer 27

:)

Answer 28

Eh you're welcome >w< I've been waiting here until you solve it while my brain is asleep

Answer 29

Take some rest Mr Zombie :P

Answer 30

Without you guys, I wouldn't be able to do so well on my test!

Answer 31

I had my test today and it wasn't that bad, I managed it pretty well!! =D

Answer 32

That's nice to know...I have a test tomorrow :'(

Answer 33

Good luck!!! You'll do fine~

Answer 34

Thanks :)
Bye..

Answer 35

Goodnight.

Answer 36

Good luck and sleep well.