Is carbon dioxide a base

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Carbonic acid buffer

In terms of quantity, carbon dioxide () and water are the most important end products of metabolism. Carbon dioxide dissolved in water reacts to form biprotonic carbonic acid (1), which dissociates in a second reaction (2).

The equilibrium of the first reaction is on the left (=). If you dissolve carbon dioxide in water, it is mainly present as and only to a small extent as. Reaction equations (1) and (2) can be drawn together and the values ​​added. The balance of the overall reaction is even more on the left: dissolved carbon dioxide reacts as a weak acid. The conjugate base is hydrogen carbonate, also called bicarbonate.

Carbon dioxide and bicarbonate form a buffer system with -optimum at =.


The carbon dioxide-bicarbonate buffer system is the most important buffer system of the blood, which is buffered on one of. The concentration ratio of the buffer substances at = can thus be calculated:

The reaction constant is temperature dependent; that of the overall reaction in the blood is at instead of at. The concentration ratio then becomes:

So there is an excess of bicarbonate, so that the buffer system works primarily against ions. Since there is a gas, what is dissolved is in equilibrium with that of the air in the lungs. This shows a special feature of this buffer system. It can not only buffer ions at the point of origin, but also remove the reaction product from the equilibrium:

+ → (↑) +

The vertical arrow indicates that the carbon dioxide is leaving the solution and going into the gas phase (leaving the system). This is why one speaks of an open buffer system.