Reef Chemistry Question of the Day #101 Bicarbonate/carbonate

[Randy Holmes-Farley]

Reef Chemistry Question of the Day #101

At what pH in seawater would there be equal concentrations of carbonate and bicarbonate ion?


A. pH 5.85
B. pH 7.00
C. pH 8.20
D. pH 8.92

Good luck!












































.

 

[wolfie2012]

D. 8.92 ;-)

 

[beaslbob]

3.48

 

[beaslbob]

get the idea I have no clue. LOL

 

[ILLA]

Ph 7

 

[Zacco]

8.92

 

[Cory]

Ph 7 because it's in the middle

 

[Steven@]

PH of 7

 

[scardall]

d) 8.92

 

[Randy Holmes-Farley]

And the answer is...D. pH 8.92

A number of my articles discuss this fact, but this one also includes a graph. Note the point where the red and white lines cross is pH 8.92 in seawater:

http://reefkeeping.com/issues/2006-10/rhf/index.php

from it:

CO₂ + H₂O ßà HCO₃^- + H⁺ pKa = 5.85
HCO₃^-ßà CO₃^--+ H⁺ pKa = 8.92
​

These pKa values imply that seawater at pH 5.85 contains equal concentrations of carbon dioxide and bicarbonate, and that seawater at pH 8.92 contains equal concentrations of bicarbonate and carbonate.

Figure 1. Relative fraction of carbon dioxide and carbonic acid (black), bicarbonate (white) and carbonate (red) in seawater as a function of pH.

Happy Reefing!

 

[beaslbob]

thanks
as usual learned something new