CO2 Level

scottward · Mar 6, 2012

An aquarium, filled with water and containing nothing else.

The tank is at 25C.

I pump in CO2 at a fixed rate and measure it at a fixed point, it measures 20ppm.

Now I change only 1 thing, I raise the temperature to 30C.

What is the CO2 level now?

It is exactly the same, 20ppm. Right?

I have more questions but not yet.

Gerryd · Mar 6, 2012

Hi,

I am fairly certain that colder water holds more c02, so I would think your ppms may be lower as the temp falls. Not much but a tiny bit..I would think as the temp falls, the water can hold a higher ppm than the higher temp.

However, I am most likely incorrect..Curious to follow this thread and where you are going with it....

Tom Barr · Mar 6, 2012

the colder the water, the higher the ppm of all dissolved gases, but since we enrich with CO2 , this is not a big factor..................th eissue has more to do with general metabolism's effect from temp changes. So called Q10 rates......

scottward · Mar 7, 2012

....I'll get to the metabolism bit (that comes later in my questions).

Ok, so I was WRONG regarding my assumption that the CO2 ppm would be the exact same in both scenarios.

So, at 25C, sure, the water will measure the said 20ppm, but once the temperature has been raised to 30C the CO2 level will DROP.

Now for my next question............why?

Why does it drop?

Given that CO2 solubility is 1450ppm @25C @1 atmosphere, and still somewhere within this vicinity on the CO2 temp chart for 30C, why would the CO2 ppm drop when I only want a measily 20ppm?

I'm struggling to understand why it would drop. Sure it would drop if I hit the CO2/temp saturation point line - but I'm nowhere near it!

There is a reason why I am asking this, and metabolism is next on my list. I might solve a long standing problem for many of us. I don't want to talk about the problem yet until I have my facts straight....

Scott.

scottward · Mar 8, 2012

...any takers?

It seems like I've asked a question that is too hard.

nipat · Mar 8, 2012

Lemme try.

It drops because it's not the equilibrium level with air which is around 0.5 PPM or so.
Unless they wouldn't have to seal soda bottles.

Rising temperature decreases the potential to hold CO2.
So it encourages more escape of CO2 from water to air.

scottward · Mar 8, 2012

nipat;80370 said:
Lemme try.

It drops because it's not the equilibrium level with air which is around 0.5 PPM or so.
Unless they wouldn't have to seal soda bottles.

Rising temperature decreases the potential to hold CO2.
So it encourages more escape of CO2 from water to air.

The partial pressure doesn't change, so this would rule out any equilibrium related stuff.

I believe the potential to hold co2 is the solubility, but as I mentioned, we are nowhere near saturation.

Are we sure they wouldn't be the same co2 level?

Biollante · Mar 8, 2012

I Feel like Charlie Brown trying to Kick the Football Out of Lucy's Hold

Hi,

Nipat is as usual, correct as to reason that explained what Tom Barr said that echoed what Gerry said.

On what basis are you so dismissive?

People are answering in good faith.:gw

I am reluctant to enter the discussion based on previous attempts at discussion.:distrust:

Given that the solubility of permanent gases decrease with increasing temperature why in the world wouldn’t partial pressure have to increase if you wanted the dissolved gasses to remain the same?

When the temperature of the system changes Henry’s constant (probably should be called coefficient) changes.

There are a number of ways to calculate Henry’s constant but for are purposes two equations derived from van 't Hoff equation (chemist’s refer to it as Vukancic-Vukovic equation) are fine.

I do not have a good way of writing the calculation in this text, were you serious or if anyone wants to know I can write it out and scan it in suppose.

I really do not mean to be critical but goodness-gracious, when you ask a question be prepared to accept the answer. :numbness:

Biollante

gsjmia · Mar 8, 2012

Not wanting to step in anything here, but just as an interesting aside, a friend of mine was a manager of a Pepsi bottling plant and he took me on a tour while the line was running.

I saw a huge tank of liquid nitrogen and asked him what it was for.

He said that they fill the cans before they put the lids on, but if they just try to crimp the lid on it would collapse the can because the aluminum sidewall is flimsy.

So, after the cans are filled, they add one or two drops of frozen/liquid nitrogen.

When the liquid nitrogen hits the warmer liquid soda, it starts to thaw and rapidly expand as it turns back to a gas.

While it is gassing, they drop the lids on and crimp them gradually (3 seperate times)--as the pressure builds up within the can they can crimp harder as the nitrogen becomes compressed the can will withstand greater squashing.

So when you pop a soda can, the pressure that gives it the "pop" is not initially C02 but it is the nitrogen escaping. Which is rapidly followed by an exit of C02 coming out of the solution.

scottward · Mar 9, 2012

Nipat is as usual, correct as to reason that explained what Tom Barr said that echoed what Gerry said.

Not quite right there I'm afraid mate. Gerry wasn't sure (but I appreciated the reply all the same). Tom didn't give me a straight answer (went off on a tangent about metabolism that had nothing immediately to do with what I was asking...

A straight Yes or No was, at least initially, what I was after.

On what basis are you so dismissive? People are answering in good faith.

Frustration mate.

I am reluctant to enter the discussion based on previous attempts at discussion.

Fair enough.

Given that the solubility of permanent gases decrease with increasing temperature why in the world wouldn’t partial pressure have to increase if you wanted the dissolved gasses to remain the same?

Starting to drift away from my original focussed questions here. I was specfically talking about the solubility temp chart earlier, quoting myself: "Given that CO2 solubility is 1450ppm @25C @1 atmosphere, and still somewhere within this vicinity on the CO2 temp chart for 30C, why would the CO2 ppm drop when I only want a measily 20ppm?".

I better technique for explaining something to somebody is to *directly* address any fundamental flaws in their thinking rather than bombarding a person with facts.

When the temperature of the system changes Henry’s constant (probably should be called coefficient) changes.

There are a number of ways to calculate Henry’s constant but for are purposes two equations derived from van 't Hoff equation (chemist’s refer to it as Vukancic-Vukovic equation) are fine.

I do not have a good way of writing the calculation in this text, were you serious or if anyone wants to know I can write it out and scan it in suppose.

I know you're just trying to help here mate, but a better approach would be to go back over my assumptions, perhaps quote something that I've said indicating my misunderstanding confusion, and set me on the right track.

I couldn't give two hoots about "Vukancic-Vukovic".

I really do not mean to be critical but goodness-gracious, when you ask a question be prepared to accept the answer.

It is perfectly ok to challenge an answer. The whole reason I asked my question in the first place was because I seek understanding. If I don't understand the answer, naturally I'm not going to accept it.

I really don't understand why you wrote this to me, it's not fair.

Scott.

scottward · Mar 9, 2012

gsjmia;80385 said:
Not wanting to step in anything here, but just as an interesting aside, a friend of mine was a manager of a Pepsi bottling plant and he took me on a tour while the line was running.

I saw a huge tank of liquid nitrogen and asked him what it was for.

He said that they fill the cans before they put the lids on, but if they just try to crimp the lid on it would collapse the can because the aluminum sidewall is flimsy.

So, after the cans are filled, they add one or two drops of frozen/liquid nitrogen.

When the liquid nitrogen hits the warmer liquid soda, it starts to thaw and rapidly expand as it turns back to a gas.

While it is gassing, they drop the lids on and crimp them gradually (3 seperate times)--as the pressure builds up within the can they can crimp harder as the nitrogen becomes compressed the can will withstand greater squashing.

So when you pop a soda can, the pressure that gives it the "pop" is not initially C02 but it is the nitrogen escaping. Which is rapidly followed by an exit of C02 coming out of the solution.

Interesting - I never knew that!

I'm thirsty now...I think I have a can of Pepsi in the fridge.....

Biollante · Mar 9, 2012

Henry's Silly Idea?

Hi,

The flaw in your thinking is the willingness to maintain a position in the face of facts.

You asked a question that is not a matter of opinion, it is a matter of fact, sorry mate, and you will have to explain what you want.

The flaw in your thinking is that you want to disregard Henry’s law, not Henry’s opinion, not Henry’s guess, but Henry's law.

I am not trying to be rude (see disclaimer), but if you want to understand Henry’s law you might want to try posting over at The Science Forum. CO[SUB]2[/SUB] adds a little complexity since it is somewhat reactive. The fact remains that there is less CO[SUB]2[/SUB] in solution at 30⁰C than 25⁰.

Given the small difference in temperatures effect on the amount of CO[SUB]2[/SUB], I think Tom Barr is correct in pointing out the metabolism change, referred to as the Q10 rate is far more significant to a discussion on plant growth.

The flaw in your thinking (logical flaw) may be your “predetermined outcome.”

Perhaps if you would state directly what you want to know someone here could help.

The Pepsi can opening is a great example of the effect of significant change on partial pressure dissolved gasses primarily CO[SUB]2[/SUB], but yes a bit of N[SUB]2[/SUB] and a few other gases as well.

An easy demonstration of the effect of temperature on dissolved gasses is to boil water, you can literally watch the N[SUB]2[/SUB] (and other dissolved gasses) being forced out of solution as a result of energy (heat in this case) added to the system.

Biollante

Biollante · Mar 11, 2012

It Was Interesting

Hi All,

I really wish folks would ask in the forum, put I have had a couple requests via email for amounts the of CO[SUB]2[/SUB] and what it means even if Scott has lost interest.:bi_polo:

So, even though Scott doesn’t wish to enlighten or engage in the conversation apparently at least a couple of folks are interested.

I have to admit I was a bit surprised there was as much difference,

amounting to something like 12.6% or so change for CO[SUB]2aq[/SUB] for each 5⁰C change in temperature. That information alone made it worth my while.

As always, I calculate this stuff longhand round off and so forth. Most notably in converting from Celsius to kelvin I truncate, ignoring the “.15⁰k” for integer values Celsius. I used published values mainly from Compilation of Henry’s Law Constants for Inorganic and Organic Species of Potential Importance in Environmental Chemistry and my out-of-date but not that out-of-date, CRC Handbook of Chemistry and Physics, 86[SUP]th[/SUP] Edition.

This is maintaining a constant amount of CO[SUB]2[/SUB] in solution at 1-atmosphere (~101.3-kpa), varying only the temperature. (The atmospheric partial pressure of CO[SUB]2gas[/SUB] at 25⁰C will cause the water to find equilibrium at 2.5X10[SUP]-4[/SUP]M, about 3.6-ppm-CO[SUB]2aq[/SUB].)

CO[SUB]2[/SUB]	10⁰C	15⁰C	20⁰C	25⁰C	30⁰C	35⁰C	40⁰C
4.544X10[SUP]-4[/SUP]M	30.6-ppm	26.5-ppm	22.9-ppm	20-ppm	17.5-ppm	15.4-ppm	13.6-ppm
7.271X10[SUP]-4[/SUP]M	48.8-ppm	42.3-ppm	36.7-ppm	32-ppm	28-ppm	24.6-ppm	21.8-ppm

Probably in this case I am just being an old gasbag[SUB]literally[/SUB], but I learned something!:glee:

Biollante

Biollante · Mar 12, 2012

Oopps... Stupid is as Stupid Does

Hi,

Henry’s law constant where is the concentration of the gas in solution and [IMG[/IMG] is the partial pressure in the atmosphere. When

refers to standard conditions (

) it is denoted

.

From van 't Hoff’s equation, a simple method describing Henry’s law as a function of temperature:

Where

is the gas constant and

is the enthalpy of the solution.
The temperature dependency is

If this works I can put equations in posts…

If it didn’t… Imagine the appropriate equations…

Biollante

Crispino Ramos · Mar 12, 2012

Biollante, The font in your post is so tiny - I could hardly read it. Could you please write in bigger font? BTW, your ideas are informative. Thank you.

Biollante · Mar 13, 2012

I Understand Your Mock, I May Well Not Be Smart Enough

Hi,

Courtesy an email from someone who actually knows about this stuff…

I should have recognized Nipat’s (therefore also Tom Barr and Gerry) answer that Le Chatelier's principle applied.

It is the constant “K” that is temperature dependent and the reason I am a bit confused

with Henry’s constant “k[SUB]H[/SUB]” being temperature dependent.

While my answers were fine, I went the long way around to get there (story of my life

).

I have a bit more complicated stuff about CO[SUB]2[/SUB] solubility if anyone is interested, no one else may care, but I have learned a lot.

Thanks Scott, good question!

Biollante

scottward · Mar 14, 2012

Bio,

I've probably got this all muddled up, but I think this is what your calculations have shown:

As per my first post in this thread, if I get the system to 30ppm @25C, then I raise the temperature to 30C whilst keeping everything else (specifically CO2 bubble rate) constant -

30ppm * .126 (12.6%)= 3.79ppm
30ppm - 3.79ppm = 26.21ppm

So the tank would probably read somewhere around 26ppm at the CO2 reference point?

I'll assume I have my head around this part and press on....

I know it's not perfectly linear, but just to keep things simple for me, I guess it would be ok (?) to say it's 0.75ppm drop in CO2 per 1C increment (3.79ppm / 5).

My actual tank at home, whereby the temperature is dictated by the ambient room temperature (no chiller/no heater), would typically do something like this over a week:

Mon - 28C
Tue - 30C (CO2 delta -1.5ppm)
Web - 31C (CO2 delta -0.75ppm)
Thu - 28C (CO2 delta +2.25ppm)
Fri - 29C (CO2 delta -0.75ppm)
Sat - 29C (CO2 delta 0ppm)
Sun - 30C (CO2 delta -0.75ppm)

...and that is of course excluding the metabolism of the plants. I know plants take some time to adapt to CO2 levels if the CO2 levels are below the demand level, but I assume that metabolism is immediate? So, having said that, I would expect the swings in CO2 level to be even more pronounced than the above.

My theory is that the reason I have so much red algae (currently the black spotty type) forming throughout my tank despite good general growth, maintenance etc etc etc, is that the CO2 is fluctuating as a result of the temperature fluctuations in the tank. The algae is sensing the change in CO2 and this is causing it to germinate.

I normally take the heater out during summer. I'm currently experimenting with putting the heater back in and setting it to the upper bar, 30C, to achieve better temperature stability.

During winter when the temperature was stabilised I still had some issues with BBA, but for different reasons (which I'm pretty sure I have addressed now).

That reminds me, I have to add something to my other thread about BBA....

Scott.

Biollante · Mar 15, 2012

Hoping Pi Day Was Evertything Everyone Hoped

Hi Scott,

I have to admit I was surprised by the amount of fluctuation in CO[SUB]2(aq)[/SUB] based on temperature.

:surprise:

I have tanks outdoors and in rooms without climate control and twice a year I tend to get pretty good algae outbreaks and other effects on plants that I attribute to changing seasons.

I confess I never considered CO[SUB]2[/SUB] fluctuation as a cause,

yet I look at some data from CO[SUB]2[/SUB] measurements and it is easy (now that I am looking for it) to see the temperature correlation.

I think you are correct that the changes in plant metabolism act as a multiplier.

I had the same thought, slowly crank up the heaters as the temperatures increase rather than removing them and see what happens. In the tanks that have injected CO[SUB]2[/SUB], increase the CO[SUB]2[/SUB] of course.:encouragement:

Almost makes me sad I will be away the next couple of summers, almost.

I have been preparing my tanks by growing “nice” algae in the tanks as a buffer.

Biollante

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