[Coral-List] FW: Ocean Acidification
Booth, Charles E. (Biology)
BOOTH at easternct.edu
Thu Jan 12 19:16:33 EST 2012
At Doug Fenner's suggestion, I am bringing this private exchange back to
Coral-List:
From: Booth, Charles E. (Biology)
Sent: Thursday, January 12, 2012 4:16 PM
To: Douglas Fenner
Subject: Re: [Coral-List] Ocean Acidification
You are correct. The last time I looked, the standard textbook value for
pure water in equilibrium with atmospheric CO2 was pH 5.6 – but, that was
based on the CO2 level of a couple of decades ago, so I suspect recent
textbook values should be a bit lower. I also suspect that pH 5.6 is a
calculated value (from the Henderson-Hasselbalch equation), as measuring the
pH of pure water (i.e.., equilibrated with purified N2 gas) using a pH
electrode is nearly impossible because the water has no conductivity or
buffer capacity (plus, there are no pH standards having the same ionic
concentration, so precise calibration of the pH meter becomes essentially
impossible even if you have a pH electrode designed for low conductivity
solutions). Our local tapwater (which comes from a nearby river) has such a
low ion concentration and alkalinity that pH measurements are essentially a
guess, as the meter readings are so unstable.
Regards,
Chuck Booth
From: Douglas Fenner <[1]douglasfenner at yahoo.com>
Reply-To: Douglas Fenner <[2]douglasfenner at yahoo.com>
Date: Thu, 12 Jan 2012 12:46:21 -0800
To: "Booth, Charles E. (Biology)" <[3]BOOTH at easternct.edu>,
"[4]coral-list at coral.aoml.noaa.gov" <[5]coral-list at coral.aoml.noaa.gov>
Subject: Re: [Coral-List] Ocean Acidification
Thanks!! I also note that it is my understanding that pure water is pH 7.0
only if it has not been in contact with air. If it has been in contact with
air it absorbs a little CO2, and since pure water is not buffered, it
actually goes slightly below pH 7.0. Sound familiar? (so if you read the
pH of distilled water but it has been in contact with the air, it will read
below 7.0 pH. Even distilled water is not really pure if it has been in
contact with very clean air. It will have N2, Oxygen, Argon, etc dissolved
in it too, anything that is in the air. The inert gases won't affect the
pH.) Cheers, Doug
_________________________________________________________________
From: "Booth, Charles E.. (Biology)" <[6]BOOTH at easternct.edu>
To: "[7]coral-list at coral.aoml.noaa.gov" <[8]coral-list at coral.aoml.noaa.gov>
Sent: Thursday, January 12, 2012 5:28 AM
Subject: [Coral-List] Ocean Acidification
Doug Fenner wrote (Wed, 11 Jan 2012 12:44:41 -0800 (PST):
'As far as I can tell, the term "acidification" means that the pH is going
down, not that the water is "acid."'
I have been using 'acidification' in this context for decades in
association
with the titration of seawater samples with HCl to measure alkalinity. I
add
HCl to the water and the pH goes down, and if I add enough acid the pH
falls
below 7.0 (I titrate to pH 4.0; I would also note here that the neutral pH
of pure water varies inversely with temperature, being 7.0 only at 25 C).
I
suspect I adopted this use from a chemistry book, or methods paper, or
from
talking with a chemist. I never encountered any opposition to my use of
acidification until 'ocean acidification' came along and skeptics started
arguing that it is an incorrect and misleading use of 'acidification,'
apparently in an attempt to deny that ocean surface pH (and alkalinity) is
decreasing measurably.
Chuck Booth
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References
1. mailto:douglasfenner at yahoo.com
2. mailto:douglasfenner at yahoo.com
3. mailto:BOOTH at easternct.edu
4. mailto:coral-list at coral.aoml.noaa.gov
5. mailto:coral-list at coral.aoml.noaa.gov
6. mailto:BOOTH at easternct.edu
7. mailto:coral-list at coral.aoml.noaa.gov
8. mailto:coral-list at coral.aoml.noaa.gov
9. mailto:Coral-List at coral.aoml.noaa.gov
10. http://coral.aoml.noaa.gov/mailman/listinfo/coral-list
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