Atmosphere, carbon dioxide and water vapour help?

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Discussion Overview

The discussion revolves around calculating the number of molecules of carbon dioxide (CO2) and water vapour in one cubic metre of air at sea level, based on their concentrations in parts per million (ppm). Participants explore the implications of these calculations and the significance of figures in their answers.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents initial calculations for the number of CO2 and water vapour molecules based on given ppm values and total molecules in air.
  • Another participant suggests that the initial approach may overlook other atmospheric components and emphasizes understanding ppm as parts per million.
  • There is a discussion about converting ppm to percentages, with some participants proposing values of 0.038% for CO2 and 0.500% for water vapour.
  • Participants debate whether to sum the ppm values directly or to calculate the total number of molecules for each gas based on the total number of molecules in air.
  • One participant expresses uncertainty about their calculations and seeks clarification on the final answers, including significant figures.
  • Another participant confirms that the numbers provided in a later post are correct but notes the importance of significant figures in the final answers.
  • There is a mention of the significance of figures in the context of the problem, with participants discussing how to determine the appropriate number of significant figures based on the values given.
  • A warning is issued regarding the sharing of specific homework questions and answers, suggesting that participants should consult their tutors instead.

Areas of Agreement / Disagreement

Participants express uncertainty and confusion regarding the calculations and the application of significant figures. There is no clear consensus on the final answers, as some participants propose different interpretations and methods for arriving at the solution.

Contextual Notes

Participants highlight the importance of significant figures in their calculations, but there is some ambiguity regarding how to apply them correctly based on the values provided. The discussion also reflects varying levels of understanding of the concepts involved.

helpemz2011
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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.
 
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helpemz2011 said:
(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
 


helpemz2011 said:
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?

helpemz2011 said:
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?
 
  • #10


What is your reasoning? How many significant figures are there in all the numbers involved in the calculation?
 
  • #11


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
 
  • #12


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.
 
  • #13


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

thanks emz
 
  • #14


Yes, that's right.
 
  • #15


thank you very very much

emz
 
  • #16


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

I advise you talk to your Open University tutor in future.

EW
OU S104 2011B
 

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