Final answer:
The ratio of the concentration of carbonic acid (H2CO3) to bicarbonate ion (HCO3-) in a buffer with a pH of 6.95 is approximately 0.372 when the Ka for carbonic acid is 4.2 x 10^-7.
Step-by-step explanation:
The pH of a bicarbonate-carbonic acid buffer is 6.95, and the Ka of carbonic acid (H2CO3) is 4.2 x 10-7. To find the ratio of the concentration of carbonic acid to that of bicarbonate ion (HCO3-), we use the Henderson-Hasselbalch equation: pH = pKa + log([HCO3-]/[H2CO3]).
By rearranging the equation to solve for the ratio [H2CO3]/[HCO3-], we get the equation [H2CO3]/[HCO3-] = 10(pH - pKa). Using the given pH of 6.95 and pKa which is the negative log of the Ka value (pKa = -log(Ka)), we calculate pKa = 6.38. Substituting these values into the formula gives us [H2CO3]/[HCO3-] = 10(6.95 - 6.38), yielding the ratio of approximately 0.372. Hence, the concentration of H2CO3 is 0.372 times that of HCO3- in this buffer system.