Answer to Question #89000 in Physical Chemistry for Sasha

Question

Buffer solutions are important in biological systems and in industry to maintain almost
constant pH values.
In the human body, one of the important buffer systems in blood involves the
hydrogencarbonate ion (HCO3-) and carbonic acid (H2CO3) which is formed when
carbon dioxide dissolves in water.
(i) Use the following equation to explain how this buffer maintains a constant pH of
7.41 even if a small amount of acid enters the bloodstream.

H2CO3 (aq) ⇄ H+(aq) + HCO3- (aq)

(ii) Provide a clear explanation in relation to the Henderson-Hasselbach equation or appropriate calculations of pH based on the above equation.

Answer 1

Solution.

(i)

$$H2CO3 = H+ + HCO3-$$

If acid enters the blood and the concentration of hydrogen ion increases, then it interacts with HCO3-, shifts the equilibrium toward H2CO3 and leads to the release of gaseous CO2.

(ii)

$$pH = pKa - log10([H2CO3]/[HCO3-])$$

If acid is added to this buffer, the ion concentration of HCO3- will decrease. This will help maintain a certain value of pH. Thus, the numerator under the sign of the logarithm will increase, and the denominator will decrease.