[Stoves] more on ocean acidification

Thu Aug 8 00:27:23 CDT 2013

Dear Friends

I have been catching up on less important correspondence after being in Asia
for a while. There is one thing that still needs to be put down like a
broken-legged horse and that of course is the idea that CO2 'acidifies' the
ocean.

Because this is a high school chemistry level topic and I know some of us
took other things - or as the drummer in my brothers class said, "I don't
remember Chemistry, I was stoned that year."

So for those of you who were also stoned that year or can't remember back
that far, here is a simple review of pH with special reference to the
oceans, CO2 and the false, badly mis-named idea that CO2 'increases the
acidity of the oceans'.

The term pH refers to one of three distinct chemical conditions which bear
no relationship to each other. One is called acidity, another is called
alkalinity and third is 'neutral'. Acidity and alkalinity are so different
that if equal in 'strength' they cancel each other completely leaving a
neutral condition. Different pH numbers refer to different conditions.

Acid solutions (it has to be a solution with water in it) have a chemistry
that has Hydrogen atoms stripped of their single electron. They are thus
positively changed and seeking an electron. This they will happily strip out
of anything passing by if they can find it, tearing the molecules to bits in
the process which is why acids 'eat' things.

Alkaline solutions (again, involving water) have molecules that have an
extra electron available (but not Hydrogen) and are thus negatively charged.
They will give away an electron happily, often wrecking the object that
receives it which is why they eat things too but by a completely different
process.

Both acidic and alkaline solutions can corrode things like metals and rocks.
One takes electrons and one gives them. Quote opposite. The two conditions
are so incompatible they cannot be present at the same time in a mixed
solution. It is one, the other or 'neutral' if neither condition is present.

If you have an alkaline solution like the ocean (pH 7.8 - 8.4 depending on
where you are, the time of day and a host of other things) and you want to
neutralise it so that all its spare electrons are taken up by various
things, you would have to add something acidic. Adding CO2 by bubbling it
through the seawater will convert some of the CO2 (about 1%) to carbonic
acid which has a deficiency of electrons and that acid will merge with
whichever passing opportunity presents itself. The corresponding alkaline
molecule will be neutralised as its spare electron will be passed to the
carbonic acid molecule (which has an H- in it) and afterwards neither will
have any charge. Both will be neutralised if the charges are balanced.

Because this happens very quickly, you cannot actually find any carbonic
acid in the ocean. Nor any other acid. The oceans are not acidic at all.
Any ocean has quite a store of available electrons. Anything acidic you dump
into the sea is quickly neutralised and the pH drops slightly because it is
closer to a neutral condition. The oceanic capacity to hand over electrons
to any passing electron gap is very, very large. There are several processes
that would begin to offer electrons but do not because the ocean is too
alkaline to allow them to get started. The ability to do this is called the
'buffering' capacity. You may remember 'Bufferin' the pill that neutralises
stomach acid. The pill is alkaline and has a large buffering capacity so it
can hand a lot of electrons over to the acid in the stomach, thus
neutralising it. If you took a whole bottle of Bufferin pills, your stomach
would not become less and less and less acidic. It would be neutralised and
then become alkaline and remains so until the spare electrons were taken up
in a neutralising process. People are, in general, alkaline and should eat
alkaline foods to remain healthy. Excess acid is a problem.

By the same measure, reducing the availability of spare electrons in the
ocean water does not at all make the water acidic because it still has many
more available electrons. It is less alkaline, but it is not acidic at all -
zero in the 'acidic scale' (there isn't one). 

In order to make a convenient metric for describing these two conditions
(which can cancel each other out very predictably) the pH scale is used.
Above 7.0 the solution has available electrons and is termed alkaline. Below
7.0 is has a deficiency of electrons and is called 'acidic'. The reason for
the use of two different terms is they are chemically dissimilar and cannot
coexist.

Acidity of a solution is often represented by the Hydrogen equivalent [H+]T
which is the total number of Hydrogen electrons that would be needed to
neutralise it.

Alkalinity is often expressed in terms of its equivalence to Calcium
Carbonate CACO3 in mg/Litre.

Q.           Can CO2 'acidify' water? 

A.            Yes, if the water is neutral to begin with, or already acidic,
like rain water. Because rain water is acidic, when it falls into the ocean
it neutralises the drops of seawater where it touches, before becoming
diluted again by the surrounding ocean. Rainwater does not impart to the
ocean any microscopic ability to withdraw electrons. It is quickly
neutralised by some seawater. When it is finished a few seconds later, the
acid has been destroyed.

Q.           If one bubbled CO2 through sea water, would it eventually
become acidic?

A.            Yes. If you were to first neutralise all the available
electrons by mopping them up, after that it would start to become acidic. It
would not considered be acidic at all until the whole body of the sample had
first been neutralised. These two conditions cannot co-exist.

Q.           What about 'acid rain'. 

A.            All rain is acidic. It is acidic because fresh water absorbs
CO2 rapidly from the atmosphere, converting about 1% into carbonic acid.
This falls into the oceans and reacts with the available alkaline molecules.
It is easy to acidify rain. It is very difficult to neutralise the oceans
because of the rocks upon which they sit which have a huge, massive
buffering capacity. There are numerous life cycles of creatures that
withdraw CO2, CO3-2 and HCO3- when it is available. Obviously CACO3 is high
on the list for uptake by creatures that make shells.

Q.           Which has a larger impact on ocean alkalinity: atmospheric CO2
or rain containing CO2?

A.            Not clear. Rain has a big effect because oceans actually have
difficulty picking up enough CO2 to drive the level much above 600 ppm
because of the limited surface area compared with the volume and the huge
buffering capacity.  Rain is much higher - about 1120 ppm CO2. Global
rainfall totals about half a million cubic kilometers per year and contains
about 600 billion tons of CO2 which is about 20 times human
<http://www.global-greenhouse-warming.com/anthropogenic-climate-change.html>
output. 

Q.           What is the mass of the oceans?

A.            1.332 billion billion tons.

Q.           Do reputable scientific organisations refer to 'acidifying' the
oceans even though that is not, chemically, what it happening?

A.            Yes. NASA does
<http://www.earthobservatory.nasa.gov/Features/OceanCarbon/> . "As we burn
fossil fuels and atmospheric carbon dioxide levels go up, the ocean absorbs
more carbon dioxide to stay in balance. But this absorption has a price:
these reactions lower the water's pH, meaning it's more acidic."

Q.           But it is less alkaline, not more acidic. Why do they write
that when it is untrue, in fact it is unscientific?

A.            I don't think anyone knows.  Perhaps they too missed Chemistry
in high school.

+++++++

Regards
Crispin

Sent: Friday, July 26, 2013 3:25 PM
Subject: [Stoves] more on ocean acidification

http://www.scientificamerican.com/article.cfm?id=noaa-scientists-embark-voya
ge-asses-ocean-acidification

-- 
Paul A. Olivier PhD
26/5 Phu Dong Thien Vuong
Dalat
Vietnam

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