# Atmosphere, carbon dioxide and water vapour help?

• helpemz2011
It is forbidden to post questions and answers on this site that have not been explicitly cleared by a tutor."In summary, this conversation is about atmospheric gases and their role in climate. The main points that were covered are that carbon dioxide and water vapour are important in helping to create an atmosphere, and that there are other molecules as well.f

#### helpemz2011

atmosphere, carbon dioxide and water vapour help??

(c)
One cubic metre (1 m3) of atmosphere at sea level contains 3.80 × 10(power of)2 ppm of CO2 and 5.00 × 10(power of)3 ppm of water vapour.
If there is a total of 2.6 × 10(power of)25 molecules in 1 m3 of air, calculate how many molecules of CO2 and water vapour there are in 1 m3 of air. Give your answers to the appropriate number of significant figures.

my workings-CO2 - 380 ppm water vapour - 5000 ppm

7.063% CO2, 92.463% water vapour

2.6 x 10(power of)25 / 100 = 2.6 x 10(power of)23
2.6 x 10(power of)23 x 7.063

CO2 1.8368 x 10(power of)24
water vapour 2.416336 x 10 (power of)25

As you can see what i have managed to do is completely loose the plot and don't even understand what i have done myself any help would be great cheers.

Welcome to Physics Forums.

(c)
One cubic metre (1 m3) of atmosphere at sea level contains 3.80 × 10(power of)2 ppm of CO2 and 5.00 × 10(power of)3 ppm of water vapour.
If there is a total of 2.6 × 10(power of)25 molecules in 1 m3 of air, calculate how many molecules of CO2 and water vapour there are in 1 m3 of air. Give your answers to the appropriate number of significant figures.

my workings-CO2 - 380 ppm water vapour - 5000 ppm

7.063% CO2, 92.463% water vapour
Well, it doesn't really work that way. Besides the CO2 and water vapour, there are other molecules as well.

Here is a better way to think about it:
If you have 1 million molecules total, then 380 of them will be CO2. That is what "ppm" means: parts per million.
So if 380 out of 1 million molecules are CO2, what percentage would that be?

hey 0.038% and 0.500%? if this is right how does this help me with the next part of the question?

cheers emz

Or would the answer simply be 2.80x10(p-o)2 ppm + 5.00x10(p-o)3 ppm = 5380 ppm

Appropriate number of significant figures - 5400 ppm of carbon dioxide and water vapour? or 5380 ppm of carbon dioxide and water vapour?

Could it be that simple I was just way way way over complicating things?

cheers emz

hey 0.038% and 0.500%? if this is right how does this help me with the next part of the question?
You're on the right track here.

So if you have "a total of 2.6 × 1025 molecules in 1 m3 of air" (quoted from your original post), and 0.038% of those molecules are water vapour molecules, how many water vapour molecules are there?

Or would the answer simply be 2.80x10(p-o)2 ppm + 5.00x10(p-o)3 ppm = 5380 ppm
Well, no. They are asking how many total molecules, of each type, are there in 1 m3 of air. Giving an answer in ppm is really not an answer to that question.

9.88x10(p-o)21 water vapour and 1.3x10(p-o)23 carbon dioxide?

i really don't know

emz

Your numbers are correct. One minor detail: the problem said to use the appropriate number of significant figures. That would change one of your answers.

so the final answer would be 9.88x10(p-o)21 of water vapour and 1.30x10(p-o)23 of carbon dioxide?

cheers emz

sorry 9.88x10(p-o)21 carbon dioxide and 1.30x10(p-o)23 water vapour?

What is your reasoning? How many significant figures are there in all the numbers involved in the calculation?

2 and 3? i really don't know my head is fried!

9.9x10(p-o)21 carbon dioxide and 1.3x10(p-o)23 water vapour?

emz

Don't guess!

Here are the numbers, how many sig figs in each?

3.80 × 102 ppm of CO2
5.00 × 103 ppm of water vapour.
2.6 × 1025 total molecules

Good luck to you.

3, 3 and 2 so they have 2 significant figures as you round to the least precise one?!

thanks emz

Yes, that's right.

thank you very very much

emz

Emz: you do realize that you are not allowed to publish TMA questions and answers don't you?