Bicarbonate

I had an aha moment yesterday while attempting to study Human Physiology when my brain was too tired.  I was studying pH and buffers.  In the body, calcium bicarbonate is in the blood to act as a buffer to prevent rapid or extreme changes in pH which can be hazardous to your overall health or status as a living person.

Bicarbonate mixed with something acidic which "donates" Hydrogen ions to the solution (H+), ends up with water and carbon dioxide:

(HCO3)+ H ---> CO2 + H2O

Limestone & acid - notice all the bubbles.   Photo source

Trying to wrap my tired brain around this buffer thing was annoying.  But then I applied some Geology and Chemistry knowledge and it all came together.  This "buffer" reaction is the same thing that happens with calcite when you put hydrochloric acid on it.


Ca(HCO3)+ H ---> CO2 + H2O + Ca

That's why it bubbles- it's creating CO2 gas.  I'm sure I've been taught this already but it's just clicking again in a new context.


In the blood, if it gets too acidic (high H+ concentration), then the bicarbonate turns it into CO2 and water.  But if the CO2 gets too high, the reaction can go the other direction and form bicarbonate.  In lab we did some experiments with changing the pH and having the bicarbonate in the solution really evened out the pH changes.  The solution without buffer jumped from a pH of 8 down to 1.8 with the addition of just 5 mL HCl.  But the solution with buffer in it only went from 8 down to about 6.5.

Okay but here is one caveat.  I just learned today that there is an intermediate step in this process -  carbonic acid.  And my Phys teacher said that the carbonic acid can't be turned into CO2 and water without the enzyme carbonic anhydrase.  Sooo that might throw a wrench into things...but maybe not.  Maybe this is why putting HCl identifies limestone so well which has a biological basis.  Perhaps the fossils in it do actually contain that enzyme?  Need to try to find out.  Trouble is finding someone who knows stuff about Geology, Chemistry, and Human Physiology.  I can find experts in each single field but I don't think I know anyone who knows all 3 to be able to tie this all together for me.  Hmmm...