Ppm, equations, atmosphere/molecules help?

  • Chemistry
  • Thread starter helpemz2011
  • Start date
  • #1

Homework Statement




At sea level, there are approximately 2.6 × 1025 molecules m-3 of the atmosphere.
One of the gases making up the atmosphere has a concentration of 3.90 × 1021 molecules m-3. What is the concentration of this gas expressed in parts per million (ppm)?


Homework Equations





The Attempt at a Solution





totally flumoxed once again lol

2.6x1025 - 3.90x1021 = 2.59961x1025

now the answer is wrong, what i have done is wrong and to get the right answer in ppm is completely going over my head for some stupid reason.

Cheers Emma
 

Answers and Replies

  • #2
Borek
Mentor
28,676
3,168
Can you give answer in %?
 
  • #3
nope tried even that is escaping me
 
  • #4
how do i get it into %?
 
  • #6
Borek
Mentor
28,676
3,168
No.

What is definition of % concentration? ppm is very similar, just instead of multiplying by 100% multiply by 106ppm.

This can be a little bit tricky, as you have to calculate ppm in terms of molecules/molecules, while usually we do it mass/mass or something like that. But other than that it is not different.
 
  • #7
ok so why multiply by 106?

I just dont get it?

sorry being extra thick today

emz
 
  • #8
Borek
Mentor
28,676
3,168
What is definition of % concentration?
 
  • #9
to be perfectly honest i just have no idea.
 
  • #10
Borek
Mentor
28,676
3,168
But you do have a book or notes or at least access to internet, and you know how to use google?
 
  • #11
helpmz2011
You may not post any of the TMA questions from The Open University on a public forum. This is considered to be cheating.
 

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