Question

The buffer system in human blood buffer is composed of HCO₃^- and H₂CO₃. (The K_a for carbonic acid is 7.9 x 10 ^-7).

a. Please identify the acidic and basic component of the buffer.

b. Please write the chemical equation that will happen when additional HCl is added into the buffer. (Hint: acids like to react with bases.)

c. Please write the chemical equation that will happen when additional NaOH is added into the buffer. (Hint: bases like to react with acids.)

d. What is the effective buffer range?

e. In order for our body to function properly, the pH of blood needs to be maintained between 7.35-7.45. If the pH of the buffer is measured to be 7.40, what is the ratio between HCO₃^- and H₂CO₃?

f. If the concentration of HCO₃^- is 5 times that of H₂CO₃, what is the pH of the buffer?

Answer 1

a).

Carbonic acid is the acidic component as it can be deprotonated.

Bicarbonate anion is the basic component which can abstract proton from an acid.

b).

HCl is a strong acid. Hence, HCl is added it will react with the conjugate base of carbonic acid to form more carbonic acid.

c).

NaOH is a strong base. Hence, addition of base results in deprotonation of carbonic acid to form more bicarbonate ions.

d).

Effective buffer range is the range of pH of the buffer which is maintained with addition of acid or base. For example, addition of a small amount of acid can result in decrease in pH by consuming bicarbonate ions. Hence, the increase is small until all the bicarbonate ions are consumed.

Similarly, with addition of base, the pH of the buffer will increase by a very small amount until all the carbonic acids are consumed. In most buffers the pH change by these addition of acid and base is +1 or -1. Hence, then effective buffer range is about 2 in most cases.

e).

pH of the buffer is given to be 7.40.

Ka of carbonic acid is

hence,

Using the Henderson-Hasselbalch equation

hence, the ratio of bicarbonate to carbonic acid concentration is about 19.95.

f)

Given that

Using the Henderson-Hasselbalch equation

Hence, the pH of the buffer is 6.8.