Question

In the bloodstream, the effective pKa for carbonic acid is 6.35. If the pH of the blood is 7.40, what percentage of the blood buffer is present as bicarbonate

Answer 1

The 91.8% is present as bicarbonate ion

Step-by-step explanation:

It is possible to find pH of a buffer using H-H equation:

pH = pKa + log [A⁻] / [HA]

Where pH is 7.40; pKa is 6.36, [A⁻] is concentration of bicarbonate ion and [HA] concentration of carbonic acid

7.40 = 6.35 + log [A⁻] / [HA]

1.05 = log [A⁻] / [HA]

11.22 = [A⁻] / [HA] (1)

As the question is in therms of percentage:

[A⁻] + [HA] = 100 (2)

Replacing (2) in (1):

11.22 = [A⁻] / 100 - [A⁻]

1122 - 11.22[A⁻] = [A⁻]

1122 = 12.22[A⁻]

91,8% = [A⁻]

The 91.8% is present as bicarbonate ion