Reef Chemistry Question of the Day #255 Oxygen Depletion in the Air

[Randy Holmes-Farley]

Reef Chemistry Question of the Day #255

The last question of the day asked how long it would take a person sitting in their living room to double the carbon dioxide level from 350 to 700 ppm. It took about an hour.

Reef Chemistry Question of the Day #254 Carbon Dioxide Formation

In that same scenario (or most any other, really) if the CO2 in the room doubles from respiration, how much has the O2 declined?

A. To 50% of the starting level
B. To 98% of the starting level
C. To 99% of the starting level
D. To 99.9% of the starting level

Good luck!





































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[JimWelsh]

Dry air has 20.95% O2, which is 209,500 PPM. I get an answer of 99.8% (209,150 / 209,500 = 0.9983) , so I'll go with "D".

 

[Randy Holmes-Farley]

Dry air has 20.95% O2, which is 209,500 PPM. I get an answer of 99.8% (209,150 / 209,500 = 0.9983) , so I'll go with "D".

If it was anyone but you, I wouldn’t mention the mistake in setting up the ratio [emoji23]

 

[brandon429]

i don't mind asking in public where did you get the 150 part of the equation 209,150 / 209,500 I know its simple but I cannot find.

 

[JimWelsh]

i don't mind asking in public where did you get the 150 part of the equation 209,150 / 209,500 I know its simple but I cannot find.

to double the carbon dioxide level from 350 to 700 ppm

209,500 - 350 = 209,150.

 

[JimWelsh]

If it was anyone but you, I wouldn’t mention the mistake in setting up the ratio [emoji23]

I'm not saying I didn't make a mistake, but I'm just not seeing it.

EDIT: Shoot, there is some water vapor involved, too, isn't there?
EDIT2: But, the H2O comes from the sugar.

 

[Randy Holmes-Farley]

CO2 has both O and C. [emoji3]

 

[Gareth elliott]

If co2 makes up .04 percent of the atmosphere. And doubling now brings the concentration to .08 i vote.
D 99.9

 

[JimWelsh]

CO2 has both O and C. [emoji3]

When discussing gasses, doesn't "PPM" refer to the number of molecules, and not their molecular weight? https://www.co2meter.com/blogs/news/15164297-co2-gas-concentration-defined

 

[Randy Holmes-Farley]

When discussing gasses, doesn't "PPM" refer to the number of molecules, and not their molecular weight? https://www.co2meter.com/blogs/news/15164297-co2-gas-concentration-defined

Ah, you are quite right. lol

I was doing it by mass but that does not fit with what most people mean by ppm in a gas, and the 350 ppm is not a normal starting point for CO2 by mass.

So you are right, once again.

 

[JimWelsh]

So you are right, once again.

Gee, I'm sorry! LOL

 

[ThunderGoose]

Glad @JimWelsh pointed out the ppm refers to molecules! Thanks! So if you produce 350 ppm CO2 you will need to take in 350 ppm O2. Intuitively it seem like A would be the correct answer. But what about concentration differences... At sea level (are we at sea level? If this is Denver we need to know!) the air is ~21% oxygen and 0.4% CO2.

Yeah, either I'm going about this all wrong or @Randy Holmes-Farley is using mass to do his calculations and I have to calculate formula weights and... Hand on. My Husband is a chemist. I'll go ask him...

 

[Randy Holmes-Farley]

Glad @JimWelsh pointed out the ppm refers to molecules! Thanks! So if you produce 350 ppm CO2 you will need to take in 350 ppm O2. Intuitively it seem like A would be the correct answer. But what about concentration differences... At sea level (are we at sea level? If this is Denver we need to know!) the air is ~21% oxygen and 0.4% CO2.

Yeah, either I'm going about this all wrong or @Randy Holmes-Farley is using mass to do his calculations and I have to calculate formula weights and... Hand on. My Husband is a chemist. I'll go ask him...

I did it originally by mass (99.9%) and Jim did it more correctly by molecules (99.8%). The closest multiple choice answer is the same, D. [emoji3]

 

[ThunderGoose]

I did it originally by mass (99.9%) and Jim did it more correctly by molecules (99.8%). The closest multiple choice answer is the same, D. [emoji3]

Ah, yeah, also read the answers wrong. This makes sense when you realize that the question is asking what percentage of the original oxygen REMAINS, not how much was used. My bad.

You'd think I'd know to read the question carefully. I'm a frickin' lecturing professor.

 

[Randy Holmes-Farley]

Ah, yeah, also read the answers wrong. This makes sense when you realize that the question is asking what percentage of the original oxygen REMAINS, not how much was used. My bad.

You'd think I'd know to read the question carefully. I'm a frickin' lecturing professor.

lol

Happy reefing.

 

[Randy Holmes-Farley]

FWIW, the main reason for posting this question was for folks to recognize how much CO2 moves in a home and how little O2 moves. Many people make the mistake of thinking that fresher air to raise pH means more O2. It probably does, but the amount it goes up is likely way less than most folks assume, even those who understand pH is just a CO2 effect.

 

[Tuan’s Reef]

FWIW, the main reason for posting this question was for folks to recognize how much CO2 moves in a home and how little O2 moves. Many people make the mistake of thinking that fresher air to raise pH means more O2. It probably does, but the amount it goes up is likely way less than most folks assume, even those who understand pH is just a CO2 effect.

Newb question here. So opening a window removes the co2 more than bring in 02?

 

[JimWelsh]

Newb question here. So opening a window removes the co2 more than bring in 02?

Yes.