Question

Phthalic acid is a diprotic acid with a pKa1 = 2.950 and pKa2 = 5.408. A solution of phthalic acid is adjusted with a strong base to a pH = 6.32. What is the principal species in the solution?

Select one:
a.phthalic acid
b.[phthalic acid] = [hydrogen phthalate]
c.hydrogen phthalate
d.[hydrogen phthalate] = [phthalate]
e.phthalate

Answer 1

The principal species in the solution with a pH of 6.32 is the hydrogen phthalate ion (C₈H₅O₄⁻).

Step-by-step explanation:

The principal species in the solution with a pH of 6.32 is the hydrogen phthalate ion, denoted as [hydrogen phthalate] or C₈H₅O₄⁻. This is because phthalic acid is a diprotic acid, meaning it can donate two protons (H⁺ ions).

At a pH above the first pKa (2.950), most of the phthalic acid will have already donated one proton and formed the hydrogen phthalate ion.

The pH of 6.32 indicates that the pH is between the two pKa values, so the principal species in the solution is the hydrogen phthalate ion.

correct option c.hydrogen phthalate

Answer 2

The principal species in the solution at pH = 6.32 is [hydrogen phthalate].

The correct answer is option d.[hydrogen phthalate] = [phthalate].

Step-by-step explanation:

The principal species in the solution at pH = 6.32 is [hydrogen phthalate]. At this pH, between the pKa1 and pKa2 of phthalic acid, the predominant species is the hydrogen phthalate ion. The solution is primarily composed of the conjugate base [hydrogen phthalate], formed by the deprotonation of the first acidic proton of phthalic acid.

This adjustment with a strong base results in [hydrogen phthalate], making option (d) [hydrogen phthalate] = [phthalate] the correct choice. The pH-dependent ionization of phthalic acid determines the equilibrium concentrations of phthalate species in the solution.

The correct answer is option d.[hydrogen phthalate] = [phthalate].