Why is sea water alkaline?

  • Thread starter vivesdn
  • Start date
  • #26
104
0
2Ca(OH)2 + 2H2CO3 ---> 2CaCO3 +4H2O.
Do you understand that on the right side that calcium carbonate is a product and the
the 4 waters are a product , from 4H+ and 4OH-
That the 4H+ , from the carbonic acid are consumed ?
And OH- is also consumed, didn't you notice?
 
  • #27
morrobay
Gold Member
773
263
Here is a reaction that removes calcium carbonate from seawater without
producing H+

Ca++ + 2HCO3- --> Ca(HCO3)2
--> CaCO3 +H2O + CO2
 
  • #28
Borek
Mentor
28,702
3,190
Here is a reaction that removes calcium carbonate from seawater without
producing H+

Ca++ + 2HCO3- --> Ca(HCO3)2
--> CaCO3 +H2O + CO2

No. You liberated carbon dioxide, it reacts with water acidifying solution. Initially solution pH was around 8.3, now it is somewhere between 5 and 6.
 
  • #29
morrobay
Gold Member
773
263
Yes it can do both: cold temperatures favor CO2 + H2O -->
2H+ + CO3-- So your right with some local conditions.

But with warmer temperatures the CO2 (gas) can be released to atmosphere
 
  • #30
Borek
Mentor
28,702
3,190
Yes it can do both: cold temperatures favor CO2 + H2O -->
2H+ + CO3-- So your right with some local conditions.

But with warmer temperatures the CO2 (gas) can be released to atmosphere

Looks unrealistic. Solubility of carbon dioxide at 15 °C is 0.197 g, at 35 °C is 0.111 g (per 100g of water, 760 mmHg of gas pressure), that means it changes about twice in the range of reasonable water temperatures. Twofold change of acid concentration means pH change in the range of several tenths of unit (below 0.5) - we are still on the acidic side.
 
  • #31
morrobay
Gold Member
773
263
Besides temperature influencing CO2 in the oceans.
There is also CO2 partial pressures in ocean and atmosphere , Henry's Law
to consider.
There is local salinity to consider.
There is CO2 uptake by marine phytoplankton and algae to consider.
Although all your posts are correct in a strict inorganic chemistry context
the carbon dioxide cycle in the oceans is more complex and synergistic than inorganic chemistry alone.
 
Last edited:
  • #32
Borek
Mentor
28,702
3,190
the carbon dioxide cycle in the oceans is more complex and synergistic than inorganic chemistry alone.

So why do you try to answer the initial question with single nonsensical reaction equations?
 
  • #33
morrobay
Gold Member
773
263
So why do you try to answer the initial question with single nonsensical reaction equations?

You dont seem to understand that a single reaction can have products that are
influenced by more than one factor in the surroundings;

Ca++ + 2HCO3- <> Ca(HCO3)2 <> CaCO3 + H2O + CO2
Here is the reaction with products that are influenced by temperature, partial pressures,
salinity and photosynthesis . Do you understand that marine plants consume the CO2 in the above product and hence stop this reaction:
CO2 + H2O > H+ + HCO3-
thereby maintaining alkalinity ?
Mabey you should reread the OP and brush up on photosynthesis
 
  • #34
Borek
Mentor
28,702
3,190
You are just trolling, and I am telling it for the second (and last) time. You showed you have no idea about the system much earlier, in many ways, proposing presence of Ca(OH)2:

Ca(OH)2 + CO2 >>shellfish> CaCO3 + H2O

suggesting existence of metallic calcium:

Ca + 2 H2O ---> Ca(OH)2 + H2

calcium oxide:

CaO + H2O --> Ca(OH)2

later you suggested that reaction which produces carbon dioxide - acid anhydride:

Ca++ + 2HCO3- --> Ca(HCO3)2 --> CaCO3 +H2O + CO2

doesn't change pH, now you call for photosynthesis to explain what happens to carbon dioxide. Trick is, if carbon dioxide is produced and then consumed, and speeds of both reactions are identical so that pH is maintained, that's a classic example of a steady state system, different from the one I was thinking about - but conceptually similar.
 
Last edited:

Related Threads on Why is sea water alkaline?

  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
9
Views
7K
  • Last Post
Replies
14
Views
2K
Replies
8
Views
16K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
4
Views
3K
  • Last Post
Replies
18
Views
29K
  • Last Post
Replies
17
Views
7K
Top