What would the initial ph of a carbonic acid - bicarbonate (ka=4.27 x 10-7) buffer be if the ratio of conjugate base to acid is 0.366 to 1?
a.
1.67
b.
1.81
c.
5.79
d.
5.85
e.
5.93

E. 5.93

Explanation:

#Plato

Use the Henderson-Hasselbalch equation:

pH = pKa + log, where A^- is the concentration of the conjugate base of the weak acid & HA is the concentration of the acid.

                    Quick note: A^- = bicarbonate and HA = carbonic acid.

Plug the known numbers into the equation:  

pH = 4.27 x 10^-7 + log

Remember, the 4.27 x 10^-7 is Ka, to change it to pKa use: -log[Ka] and pKa will be 6.37.

Thus,

pH = 6.37 + log(0.366) = 5.93305321

5.93 is the intial pH

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