Question

In our body, carbon dioxide $\left({CO}_2\right)$ combines with water $\left(H_{2}O\right)$ to form carbonic acid.
$H_{2}O+{CO}_2⟶H_2{CO}_3$
Carbonic acid undergoes dissociation as,
$H_2{CO}_3\rightleftharpoons H^{+}+H{CO}_3^{-}$
During the physical and mental stress, the rate of respiration increases, which results in the decrease in concentration of ${CO}_2$ in the blood. What will be the effect on pH of human blood during the stress?

• A. Decreases
• B. Remains same
• C. Increases
• D. Cannot be predicted

Answer 1

Answer: (A)

Decreases

In our body following ionic equilibrium are present.

$H_{2}O+{CO}_2\rightleftharpoons H_2{CO}_3⟶\left(i\right)$

$H_2{CO}_3\rightleftharpoons H^{+}+{HCO}_3^{-}⟶\left(ii\right)$

If rate of respiration increases, the concentration of ${CO}_2$ decreases in the blood. As a result concentration of $H_2{CO}_3$ (carbonic acid) also decreases according equation $1$. Now $H_2{CO}_3/{HCO}_3^{-}$ system acts on buffer. So to maintain equilibrium $\left(ii\right)$ more concentration of $H^{+}$ will be needed. As a result $pH$ decreases.