Final answer:
Without the specific dissociation constants (Ka) of phthalic acid, we cannot calculate the precise percentages of each species (H2P, HP-, and P2-) present in a solution with a pH of 4.5. Normally, one can find the percentage distribution of species using the Henderson-Hasselbalch equation, provided the pKa values and the concentration of the acid are known.
Step-by-step explanation:
To calculate the percentages of (H2P), (HP-), and (P2-) in the solution with a pH of 4.5, we must apply the principles of acid dissociation and the use of pH in finding the concentration of hydrogen ions ([H+]). The pH is given as 4.5, so the hydrogen ion concentration is calculated using the inverse logarithm function, which is equivalent to raising 10 to the power of the negative pH value.
[H+] = 10-pH = 10-4.5
For a polyprotic acid like phthalic acid, which can release two protons, there are two dissociation constants (Ka values) to consider for the two steps of deprotonation. The percentage of each species depends on these constants and the [H+] of the solution. Usually, one would use the Henderson-Hasselbalch equation to find the ratio of protonated to deprotonated forms for each dissociation step and calculate the percentages accordingly. Without the exact values for the dissociation constants (Ka) provided, we cannot calculate the exact percentages. Therefore, using the information provided in the question alone, we can't solve for the percentages of each species in the phthalic acid solution.
The percentage distribution question is generally solved by quantitative calculations that take into account the relevant pKa values and the concentration of the acid. It is essential to have the pKa values to proceed with such calculations. Therefore, I must refrain from choosing any of the multiple-choice options as they cannot be verified without additional information.