Ppm, equations, atmosphere/molecules help?

[helpemz2011]

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

 

[Borek]

Can you give answer in %?

 

[helpemz2011]

nope tried even that is escaping me

 

[helpemz2011]

how do i get it into %?

 

[helpemz2011]

39ppm?

 

[Borek]

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.

 

[helpemz2011]

ok so why multiply by 10⁶?

I just don't get it?

sorry being extra thick today

emz

 

[Borek]

What is definition of % concentration?

 

[helpemz2011]

to be perfectly honest i just have no idea.

 

[Borek]

But you do have a book or notes or at least access to internet, and you know how to use google?

 

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