Question

The pH of blood plasma is 7.40. Assuming the principal buffer system is HCO3-/H2CO3, calculate the ratio [HCO3-]/[H2CO3]. Is this buffer more effective against an added acid or an added base?

Answer 1

Given that

The pH of blood plasma = 7.40.

[HCO3^-]/[H2CO3] = ?

pKa = 6.37 for .H2CO3.

Formula to calculate the pH of any buffer we use following equation;

, pKa = pH + log[base/acid]

so, pH = pKa + log{[HCO3^-]/[H2CO3

Let us put all the known values,

7.40 = 6.37 + log{[HCO3^-]/[H2CO3]}

so, log{[HCO3^-]/[H2CO3]} = 7.40 - 6.37

log{[HCO3^-]/[H2CO3]} = 1.03.............(logarithmic form)

[HCO3^-]/[H2CO3] = 10^1.03.............(exponential form)

[HCO3^-]/[H2CO3] = 10.72.

This buffer is an example of slightly basic thus it will be more effective against the added acid.