[Hagrid]

the following equations (taking an average seawater temperature of 25°C  for the Great Barrier Reef system) describe the effect (dissolution) that increasing atmospheric CO2 levels will ultimately have on corals (carbonates) due to ocean acidification:
log K25°C = -1.5      CO2 + H20  HCO3-(aq) + H+(aq)
log K25°C = 10.3      H+(aq) + CO32-(aq)  HCO3-(aq)
log K25°C = -8.5      CaCO3 (coral)  Ca2+(aq) + CO32-(aq)
For a 0.15 decrease in pH (from 8.0 to 7.85) of seawater, estimate how much less CO32-(aq) (molecular weight = 60g/mole) will be available to form coral (assuming that calcium is not a limiting factor).  You may give your answer as either ppm or μmol/kg.

There is more to this question but it is subsequently and I can do it, but if I have forgotten something I can include it (though I am confident with that part)
   

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I would have thought the steps be this:

1st equation: pH = - log [H+] , so we can work out the concentration of H+ based on the pH being 8
Concentration times volume will give me the number of moles (n)
I can use this n and the volume of liquid to calculate the concentration CO32- in the third equation.
I then repeat these above 3 steps for the pH being 7.85
I subtract the the result of pH 8 and pH 7.85


I highly doubt I am right and of course I can't reach and answer:....there is extra info I have not used and some info I don't have.


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I'm a geology student taking a  hybrid geology and chemistry course (geochem). My chemistry is very very weak but there aren't many chemistry based questions.

You're help is really appreciated. This is another sample exam question for my exam next week.

[Borek]

No redox here, just an acid/base equilibrium.

See if this page helps: http://www.chembuddy.com/?left=pH-calculation&right=pH-polyprotic-acid-base

(specifically equation 9.13 derived there).