How does $ce{H2CO3}$ form in the blood with a ratio of 1:20 with $ce{HCO3-}$ if there are not enough $ce{H+}$ ions
In our bodies, the balance of acids and bases, known as pH, is tightly regulated to maintain homeostasis. One of the key players in this regulation is the bicarbonate-carbonate buffer system, which helps to maintain the pH balance in the blood.
The formation of carbonic acid ($ce{H2CO3}$) in the blood starts with the reaction between carbon dioxide ($ce{CO2}$) and water ($ce{H2O}$). This reaction is catalyzed by an enzyme called carbonic anhydrase, which is present in red blood cells. The reaction can be represented as follows:
$ce{CO2 + H2O H2CO3}$
Carbon dioxide in the blood, which is produced as a waste product of cellular respiration, diffuses into red blood cells. Inside the red blood cells, the enzyme carbonic anhydrase speeds up the reaction between carbon dioxide and water, resulting in the formation of carbonic acid. This is a reversible reaction, meaning that carbonic acid can break down back into carbon dioxide and water
The carbonic acid then dissociates into hydrogen ions ($ce{H+}$) and bicarbonate ions ($ce{HCO3-}$):
$ce{H2CO3 H+ + HCO3-}$
The 1:20 ratio between $ce{H2CO3}$ and $ce{HCO3-}$. The concentration of $ce{H2CO3}$ in the blood is typically very low because it is in equilibrium with carbon dioxide, which is usually present at low concentrations in the blood. However, bicarbonate ions ($ce{HCO3-}$) are much more abundant in the blood
Even if there are not enough hydrogen ions ($ce{H+}$) available in the blood, the bicarbonate ions can still be converted back into carbonic acid. This is because the reaction can shift to the right, producing more $ce{H2CO3}$, if the concentration of bicarbonate ions is high enough. In other words, even without an excess of hydrogen ions, the equilibrium between $ce{H2CO3}$ and $ce{HCO3-}$ can be maintained at a ratio of 1:20 by the reversible reaction
It is important to note that this buffer system plays a crucial role in maintaining the pH balance in our blood. When there is an excess of acid (an increase in hydrogen ions), the carbonic acid will dissociate, releasing hydrogen ions, which can help to neutralize the excess acid. On the other hand, when there is an excess of base (a decrease in hydrogen ions), the equilibrium will shift to the left, producing more bicarbonate ions to balance out the blood pH
Overall, the bicarbonate-carbonate buffer system in our blood helps to regulate the pH balance by converting carbon dioxide into carbonic acid and bicarbonate ions, allowing for the maintenance of a relatively constant ratio of 1:20 between $ce{H2CO3}$ and $ce{HCO3-}$, even in the absence of excess hydrogen ions
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