Experiment 6: Acid-Base Equilibrium Potentiometric Titration of Weak Acids

What is the purpose of observing pH changes in monoprotic and polyprotic titrations?

To determine the equivalence point(s) and experimentally determine the Ka for weak acids.

What is a titration curve?

A graphical representation of pH vs. the amount of strong base added, showing different regions during the titration process.

What are the four regions of a titration curve for a weak monoprotic acid?

There is a buffer region before the equivalence point, a sharp rise near the equivalence point, a buffer region after, and a plateau.

What is the equivalence point in a titration?

The point at which the amount of titrant added is stoichiometrically equivalent to the amount of substance being titrated.

How can the titration equivalence point be determined?

By interpreting the titration curve and using a gran plot.

What is the significance of the inflection points in a titration curve?

They correspond to the pKa values of the weak acid and are used to calculate acid dissociation constants.

What is the role of a pH meter in potentiometric titration?

It measures the pH by detecting the change in electric potential as the titration progresses.

What type of acid is phosphoric acid classified as?

A triprotic (or polyprotic) acid.

What dissociation steps characterize phosphoric acid?

H3PO4 ⇌ H2PO4- + H+; H2PO4- ⇌ HPO42- + H+; HPO42- ⇌ PO43- + H+.

What is the initial pH of the acid solution used in the weak monoprotic acid titration?

It is measured before adding any titrant.

What is the endpoint of a titration?

The point during the titration when there is a significant change in pH, indicating complete neutralization.

How was the titration curve for acetic acid plotted?

By continuously monitoring the pH as NaOH was incrementally added until the equivalence point.

What calculations were performed to determine Ka for acetic acid?

Using initial pH and molarity, pH at half-equivalence point, and pH at equivalence with sodium acetate concentration.

How many graphs were created in the analysis of acetic acid titration?

Three graphs: a titration curve, a modified Gran plot, and a zoomed-in Gran plot near the equivalence point.

What is the method for calculating Ka1 of phosphoric acid?

Using the initial pH and molarity of the acid and the pH at the half-equivalence point.

How can Ka2 for phosphoric acid be determined?

From the pH halfway between the first and second equivalence points.

What additional graph was created in the titration of phosphoric acid?

A modified Gran plot.

Why might pKa2 and pKa3 not be discernible in polyprotic acids during titration?

If the pH of the solution approaches the pH of the titrant base.

What was used to monitor the pH during the titration?

A pH meter.

What was the concentration of NaOH used in the titrations?

0.35 M.

What is the initial pH of the weak polyprotic acid used in the experiment?

It is recorded before titration commences.

What indicates the neutralization of protons in a polyprotic acid titration?

Notable changes in pH observed at distinct equivalence points.

What methodology was used to compare Ka values for acetic acid?

Compared calculated Ka values to those found in Table 17.5 of Tro.

What experimental method was used to analyze weak acid-strong base titration?

Potentiometric titration.

What does the inflection point in the buffer region correspond to?

The pKa value of the weak acid.

How were the molarity of acetic acid and its Ka compared in the experiment?

Using three different methods to calculate and compare results.

What tool acts as both a pH meter and a galvanic cell in this experiment?

The pH meter.

What type of acid was used for the weak monoprotic acid titration?

Acetic acid.

What does each step of phosphoric acid titration reflect regarding its structure?

Each step represents the deprotonation of the acid, leading to different species in solution.

How is the endpoint of the titration visually confirmed?

By monitoring the significant change in pH during the titration process.