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Author Topic:   Quick Questions, Short Answers - No Debate
Coragyps
Member
Posts: 5414
From: Snyder, Texas, USA
Joined: 11-12-2002
Member Rating: 6.0


Message 286 of 569 (682630)
12-04-2012 8:52 AM
Reply to: Message 285 by foreveryoung
12-04-2012 4:41 AM


Re: Ocean acidification
There is some dissolved CO2, as CO2, in seawater at the normal pH (around 8.1), and the solubility decreases with increasing temperature. So the acidity will decrease (the pH will rise) with an increase in temperature, if all else is constant.
Pressure enters into this in a big way, as well, as it affects solubility of gasses. So it's only simple in the surface layer where you have the opportunity to establish equilibrium with atmospheric CO2.

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RAZD
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Posts: 20332
From: the other end of the sidewalk
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Member Rating: 3.6


Message 287 of 569 (682634)
12-04-2012 9:06 AM
Reply to: Message 285 by foreveryoung
12-04-2012 4:41 AM


Re: Ocean acidification
Hi foreveryoung,

CO2 + H2O = H2CO3 = H + HCO3 = 2H + CO3

Don't know how to type the ions in.

You got the subscript down, and superscript is similar: H<sup>-</sup> = H-


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RAZD
Member
Posts: 20332
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.6


Message 288 of 569 (682638)
12-04-2012 9:31 AM
Reply to: Message 285 by foreveryoung
12-04-2012 4:41 AM


Re: Ocean acidification
Hi foreveryoung,

CO2 + H2O = H2CO3 = H + HCO3 = 2H + CO3

Don't know how to type the ions in.

You got the subscript down, and superscript is similar: H<sup>-</sup> = H-

So you could do:

CO2 + H2O = H2CO3 = H- + HCO3+ = 2H- + CO3++

When carbon dioxide is dissolved in the ocean, does all of it immediately react with water to form carbonic acid or is there dissolved, unreacted carbon dioxide in the water too?

All three can exist in the ocean, but more so at the surface. See Dr. Adequates article on
Introduction To Geology Message 118

Enjoy


we are limited in our ability to understand
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Rebel American Zen Deist
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foreveryoung
Member (Idle past 89 days)
Posts: 920
Joined: 12-26-2011


Message 289 of 569 (682654)
12-04-2012 11:41 AM
Reply to: Message 286 by Coragyps
12-04-2012 8:52 AM


Re: Ocean acidification
I can see that the solubility of CO2 decreases with increasing temperature but how is the disassociation of HCO3 into H+ and CO3- affected by an increase in ocean temperature at the surface?

Edited by foreveryoung, : No reason given.

Edited by foreveryoung, : No reason given.

Edited by foreveryoung, : No reason given.


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crashfrog
Inactive Member


(1)
Message 290 of 569 (682685)
12-04-2012 3:47 PM
Reply to: Message 289 by foreveryoung
12-04-2012 11:41 AM


Re: Ocean acidification
Dissociation happens because it's free-energy favorable, so the extent to which it happens is determined by the free energy (delta-G). Recall that delta-G = RT ln(K). Take the derivative of K in terms of T and you'll see how the dissociation constant of HCO3 is affected by an increase in ocean temperatures.

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Coragyps
Member
Posts: 5414
From: Snyder, Texas, USA
Joined: 11-12-2002
Member Rating: 6.0


Message 291 of 569 (682689)
12-04-2012 4:51 PM
Reply to: Message 289 by foreveryoung
12-04-2012 11:41 AM


Re: Ocean acidification
I don't have a CRC Handbook of the proper age to look that Gibbs Free Energy up - but I'm going to bet that the change in solubility at real ocean temperatures overwhelms any thermodynamic terms anyway.

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foreveryoung
Member (Idle past 89 days)
Posts: 920
Joined: 12-26-2011


Message 292 of 569 (682693)
12-04-2012 5:37 PM
Reply to: Message 290 by crashfrog
12-04-2012 3:47 PM


Re: Ocean acidification
(6)Loge(Ka' / Ka) = ÄHo / R . (1/T-1/T')

Using this equation, it shows that an increase in temperature makes for a greater disassociation constant. This tells me that as the ocean surface warms, more HCO3 disassociates into H+ and CO3-

So, you don't even have to have more CO2 dissolved into the ocean to get greater acidity. All it takes is an increase in ocean surface temperatures.


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Coragyps
Member
Posts: 5414
From: Snyder, Texas, USA
Joined: 11-12-2002
Member Rating: 6.0


Message 293 of 569 (682694)
12-04-2012 5:56 PM
Reply to: Message 292 by foreveryoung
12-04-2012 5:37 PM


Re: Ocean acidification
So, you don't even have to have more CO2 dissolved into the ocean to get greater acidity. All it takes is an increase in ocean surface temperatures.

More dissolved CO2 at constant temperature lowers the pH. Higher temperature at constant CO2 content lowers the pH. But solubility of CO2 in water drops by about 50% from 10C to 30C, so I still wonder if a rise in temperature - all alone - might actually raise surface pH.

Of course, when that surface water circulates down to the abyss where it's uniformly cold, the CO2 content will tell the tale. More = lower pH down there at the bottom.


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foreveryoung
Member (Idle past 89 days)
Posts: 920
Joined: 12-26-2011


Message 294 of 569 (682696)
12-04-2012 6:13 PM
Reply to: Message 293 by Coragyps
12-04-2012 5:56 PM


Re: Ocean acidification
It all depends on which factor carries the greatest weight in le Chateliers principle.....either greater dissolved CO2 or greater temperature affect on raising the disassociation constant. Greater surface temperatures dissolve less CO2 at the surface and greater surface temperatures change the point of equilibrium to greater disassociation of HCO3. An experiment could be done to find out how much CO2 would have to be dissolved in a liter of sea water to change the pH by 30%, which is the amount said to have occurred in the oceans since records have been kept. Another experiment could be done that raises the temperature of one liter of sea water by.7C, the amount of temperature gain in the same period of time, and see the change in pH. Calculations could then be done to see if temperature has more of an effect than CO2 in raising acidity levels.

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crashfrog
Inactive Member


(1)
Message 295 of 569 (682700)
12-04-2012 7:42 PM
Reply to: Message 294 by foreveryoung
12-04-2012 6:13 PM


Re: Ocean acidification
It all depends on which factor carries the greatest weight in le Chateliers principle.....either greater dissolved CO2 or greater temperature affect on raising the disassociation constant.

Well, that's not going to be hard to figure out at a back-of-the-envelope level. A 50% change in solubility across a 20 degree difference is huge. Over the same temperature, though, the free energy will only change by about 6%. So the solubility is clearly your first-order factor.


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foreveryoung
Member (Idle past 89 days)
Posts: 920
Joined: 12-26-2011


Message 296 of 569 (682729)
12-05-2012 12:05 AM
Reply to: Message 295 by crashfrog
12-04-2012 7:42 PM


Re: Ocean acidification
I just figured that out for a change in temperature of .7C using the vant hoff equation. The resulting change in pH was miniscule compared to the supposed change of 30% in pH over the same period of time. Even though both disassociation reactions are endothermic, it takes a much greater change in temperature to change the pH by that much.

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foreveryoung
Member (Idle past 89 days)
Posts: 920
Joined: 12-26-2011


Message 297 of 569 (682732)
12-05-2012 1:09 AM


another cause of ocean acidification
It is known that colder water can dissolve more carbon dioxide. The deep ocean is more acidic than the surface ocean because of that. The thermohaline circulation brings cold deep water to the surface at certain points. If that upwelling occurs at a steady pace over time, then the extra acidity it brings to the surface cannot be taken into consideration when considering causes of increased ocean acidity. However, if that upwelling occurs at a faster past than normal,an increase in ocean acidity can logically be blamed on it. Scientists claim that an increase in ocean surface temperatures can speed up the thermohaline circulation. If ocean surface temperatures are not rising due to an increased greenhouse effect but due to other causes, an increase in ocean acidity can be blamed on the thermohaline circulation instead of increased carbon dioxide being dissolved.

  
foreveryoung
Member (Idle past 89 days)
Posts: 920
Joined: 12-26-2011


Message 298 of 569 (683523)
12-11-2012 2:44 PM


question for geologists
I am currently almost through with a course in mineralogy. I am having trouble consistently telling the difference between quartz and nepheline and alkaline feldspar that lack obvious twinning. I am also having trouble telling the difference between biotite and hornblende especially when the biotite is very weathered. I am talking about thin sections for these minerals and not hand sample specimens of them.

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mmo02old1 
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Posts: 2
Joined: 12-11-2012


Message 299 of 569 (683583)
12-11-2012 9:23 PM
Reply to: Message 8 by RAZD
11-25-2007 8:43 PM


Re: Oort cloud question.
Hi, I an new to here, nice to see you!

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roxrkool
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Posts: 1497
From: Nevada
Joined: 03-23-2003


(1)
Message 300 of 569 (683587)
12-11-2012 10:03 PM
Reply to: Message 298 by foreveryoung
12-11-2012 2:44 PM


Re: question for geologists
It's been a while since I've looked at thin sections, but what I remember is that quartz is often anhedral, black/white, and clear with no fractures. You can often find small inclusions of other minerals as well as tiny fluid inclusions, and they are often aligned. When deformed, quartz often displays undulatory extinction, sometimes having a granular appearance.

Unless they are interstitial, the feldspars often have twinning and are subhedral to euhedral. And if I remember correctly, cleavage planes are more common and visible, and since feldspars will alter to clay fairly easily, you will often see some sort of 'texture' to the feldspars, particularly along cleavage planes. Fluid inclusions are less common.

Play with the light source. Sometimes you can see cleavages and regular fracture patterns with the feldspars, whereas the quartz will remain smooth.

What I remember about biotite is the brown color (in plane light), the feathery/splintery ends, and bird's eye extinction. Bird's eye extinction is a 'rough' or mottled appearance. I believe this is because the biotite is made up of tiny plates of biotite and when bent up/broken, will go extinct at different angles.

Hornblende, on the other side, often has clean, straight edges (unless being replaced by biotite), is often euhedral/subhedral, and has visible 120/60 degree cleavage, visible as fractures.

Hope that helps some.


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