Question

3. The human body has devised an excellent method to keep the body pH under control.

a. What principle underlies the constant pH of human blood, and how does the blood achieve this? (1 point)

b. Use Le Châtelier’s principle to explain how the human body is protected against low pH after excessive exercise. (1 point)

c. Use the concept of the equilibrium constant to explain why neutrality in the blood depends on the concentrations of [H⁺] and [OH^-] rather than pH. (1 point)

Answer 1

3.a. The principle behind the constancy of the pH of blood is the Buffering Principle i.e Blood acts like a Buffer solution which restrict the change of pH in a huge amount if a small amount of Acid or base is added.

• The Blood maintain its pH by the Buffer system known as Carbonic Acid/Bicarbonate Buffer.The following equilibria is taking place in the blood constantly to maintain its pH-

$CO_{2}+H_{2}O\rightleftharpoons H_{2}CO_{3}\rightleftharpoons HCO_{3}^{-}+H^{+}$ ---1

If you drink water,it reacts with the Carbon Dioxide in the Blood to produce Carbonic Acid (
H2CO3
) which decrease the pH level of blood but it soon dissociates into Bicarbonate ion(
HCO
) which again raise the pH level.

3.b. As we do extensive exercise,our body uses
O2
from hemoglobin and release $CO_{2}$ and $H^{+}$ due to which the pH levels of our blood drops from the standard 7.4 to approx 7.1-7.2. The Buffer system doesn't allow a significant drop in pH as more carbonic acid is produced, the equilibrium 1 sets off and produces Bicarbonate ions very quickly according to Le-Chatelier's Principle to balance the pH level again (According to Le-Chatelier's principle,the forward reaction favors if there is more supply of reagent which is Carbonic acid here).

3.c.  

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