Answer:
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