[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
    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.
   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
     with the titration of seawater samples with HCl to measure alkalinity. I
     HCl to the water and the pH goes down, and if I add enough acid the pH
     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).
     suspect I adopted this use from a chemistry book, or methods paper, or
     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
   Coral-List mailing list
   [9]Coral-List at coral.aoml.noaa.gov


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