Molarity, pH, Titration

A 50.0 mL sample of an acid, HA, of unknown molarity is titrated, and the pH of the resulting solution is measured with a pH meter and graphed as a function of the volume of 0.100 M NaOH added.

At point R in the titration, which of the following species has the highest concentration?

• HA

• A^-

• H₃O⁺

• OH^-

A solution of a weak monoprotic acid is titrated with a solution of a strong base, KOH. Consider the points labeled (A) through (E) on the titration curve

that results, as shown below.

The point at which the concentrations of the weak acid and its conjugate base are approximately equal is

• A

• B

• C

• D

• E

An unknown acid is dissolved in 25 mL of water and titrated with 0.100 M NaOH. The results are shown in the titration curve above. Which of the following could be the unknown acid?

• Fluoroacetic acid, pKa = 2.6

• Glycolic acid, pKa = 3.8

• Propanoic acid, pKa = 4.9

• Hypochlorous acid, pKa = 7.5

• Boric acid, pKa = 9.3

The graph above shows the titration curve that resulted when a sample of 0.1 M monoprotic acid was titrated with a solution of NaOH. Based on the graph, the pKa of the acid is closest to

• 3.0

• 4.0

• 6.0

• 8.0

• 12.0

A 0.35 g sample of Li(s) is placed in an Erlenmeyer flask containing 100 mL of water at 25°C. A balloon is placed over the mouth of the flask to collect the hydrogen gas that is generated.

After all of the Li(s) has reacted with H₂O(l), the solution in the flask is added to a clean, dry buret and used to titrate an aqueous solution of a monoprotic acid. The pH curve for this titration is shown in the diagram below.

On the basis of the pH curve, the pKa value of the acid is closest to

• 4

• 5

• 8

• 12

B(aq) + HCl(aq) ↔ HB⁺(aq) + Cl^-(aq)

The graph above shows the titration curve for an aqueous solution of a weak base, B, with HCl as the titrant. Based on the graph, which of the following best estimates the pKa of HB⁺?

• 12.0

• 10.8

• 6.0

• 1.8

A 50.0 mL sample of an acid, HA, of unknown molarity is titrated, and the pH of the resulting solution is measured with a pH meter and graphed as a function of the volume of 0.100 M NaOH added.

At which point on the titration curve is [A^-] closest to twice that of [HA] ?

• R

• S

• T

• U

When a strong acid is titrated with a strong base using phenolphthalein as an indicator, the color changes abruptly at the endpoint of the titration and can be switched back and forth by the addition of only one drop of acid or base. The reason for the abruptness of this color change is that

• a large change in pH occurs near the endpoint of the titration

• a buffer solution exists at the endpoint of the titration

• phenolphthalein is a strong proton donor

• the pH of water is very resistant to change

• phenolphthalein is much more sensitive to the pH of a solution than most other indicators

A student performs an acid-base titration and plots the experimental results in the graph above. Which of the following statements best explains the experimental findings?

• A strong acid was titrated with a strong base, as evidenced by the equivalence point at pH = 7.

• A strong acid was titrated with a strong base, as evidenced by the equivalence point at pH > 7.

• A weak acid was titrated with a strong base, as evidenced by the equivalence point at pH > 7.

• A weak acid was titrated with a weak base, as evidenced by the equivalence point at pH approximately 7.

NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)

To determine the concentration of a NaOH(aq) solution, a student titrated a 50. mL sample with 0.10 M HCl(aq) . The reaction is represented by the equation above. The titration is monitored using a pH meter, and the experimental results are plotted in the graph below.

At the point labeled R on the pH curve, which of the following ions are present in the reaction mixture at a concentration greater than 0.01 M?

• Na⁺ and Cl^- only

• Na⁺, Cl^-, and H⁺ only

• Na⁺, Cl^-, and OH^- only

• Na⁺, Cl^-, H⁺, and OH^-

Tags

NGSS.HS-PS1-2