Ocean acidity/CO2 Solubility

Right, I don't usually post stuff like this because in due course i manage to work it out. However, this thing in storylines (i.e. not the core text book) is part of the spec, and it's about CO2 dissolving in the Oceans

CO2(g) <----------> CO2(aq)

CO2(aq) + H2O(L) <----------> H+(aq) + HCO3-(aq)

HCO3-(aq) <----------> H+(aq) + CO32-(aq)

Adding these together gives:

CO2(g) + H2O(l) <----------> 2H+(aq) + CO32-(aq)

Now, I follow this so far, but then the book says something which i don't quite get, and neither does my teacher.

"It can be seen that times of high atmospheric carbon dioxide levels will lead to more carbon dioxide dissolving in the oceans. The oceans do not become increasingly acidic because the excess carbonate ions precipitate out as CACO3."

I dont get the bit in bold. It makes no sense. Surely if carbonate is precipitated out, then the equilibrium will shift right and just cause even more H+ to appear?

Any help, or discussion is welcomed. Rep availible for the best input :eek:

Cheers

Reply 1

username68316

OP

3

Hmm, I don't really want to rep you, help bot.

Reply 2

arpeggio

12

Try this?

I don't know how much help it is, but if you scroll down to the bottom then it has stuff about ocean acidity. It seems to contradict what your book says though, as it says pH decreases as carbon dioxide levels increase :confused:

Maybe the book's wrong?

Reply 3

ChemistBoy

16

Nathan Ley3

Right, I don't usually post stuff like this because in due course i manage to work it out. However, this thing in storylines (i.e. not the core text book) is part of the spec, and it's about CO2 dissolving in the Oceans

CO2(g) <----------> CO2(aq)

CO2(aq) + H2O(L) <----------> H+(aq) + HCO3-(aq)

HCO3-(aq) <----------> H+(aq) + CO32-(aq)

Adding these together gives:

CO2(g) + H2O(l) <----------> 2H+(aq) + CO32-(aq)

Now, I follow this so far, but then the book says something which i don't quite get, and neither does my teacher.

"It can be seen that times of high atmospheric carbon dioxide levels will lead to more carbon dioxide dissolving in the oceans. The oceans do not become increasingly acidic because the excess carbonate ions precipitate out as CACO3."

I dont get the bit in bold. It makes no sense. Surely if carbonate is precipitated out, then the equilibrium will shift right and just cause even more H+ to appear?

Any help, or discussion is welcomed. Rep availible for the best input :eek:

Cheers

You're right it makes no sense. The reason why the oceans wouldn't become too acidic is due to the currents and flow in our oceans. However in 2004 the Royal Society launched an investigation into rises in ocean acidity linked with rises in atmospheric CO2. It is my professional opinion as a chemist that the book is wrong.