17.3.5 Weak Base-Strong Acid Titration

Question 1

Weak Base-Strong Acid Titration

Answer 1

• The titration curve of a weak base-strong acid titration has many components in common with a weak acid-strong base titration curve.
• The pH of a weak base-strong acid titration is below 7 at the equivalence point.

Question 2

note

Answer 2

• The titration curve of a weak base-strong acid titration has many components in common with a weak acid-strong base titration curve.
• At the beginning of the titration, the solution is entirely weak base. Calculating the pH is a base-dissociation constant (K b ) problem.
• As strong acid is added, a buffer region and the
  half-equivalence point are reached. At the half-equivalence point, there are equal amounts of weak base and the conjugate acid; at this point pH = pK a .
• Past the equivalence point, the buffer capacity of the buffer created by the weak base and its conjugate acid is exceeded and the pH of the solution drops dramatically.
• The pH of a weak base-strong acid titration is below 7 at the equivalence point.
• At the equivalence point there is only conjugate acid ion in solution. This is an acid-dissociation constant (K a ) calculation.
• Problem: What is the pH of the solution at the equivalence point after 100.0 mL of 0.100 M ammonia is titrated with 100.0 mL of 0.100 M hydrochloric acid?
• The K a of ammonium ion (the conjugate acid of ammonia) is 5.6 x 10 –10 (at 25 ̊C). Since the final volume is twice the initial volume, the initial concentration of ammonium ion at the equivalence point is 0.05 M. These values can be used to solve for the concentration of H + (5.29 x 10 –6 M). The pH of the solution is 5.28. This value makes sense—ammonium ion is a weak acid, so the pH should be slightly below 7.

Question 3

We examined the titration of a weak base with a strong acid.

Which statement about this reaction is not correct?

Answer 3

We need to know the equilibrium concentrations of NH3 , H3O+, NH4+, and H2O to calculate the value of Kb for this reaction.

Question 4

We examined the titration of a weak base, NH3, with a strong acid, HCl.
Ka = 5.6*10^-10
Suppose that we start with 100 mL of 0.150 M NH3 titrated with 0.150 M HCl. What is the pH of the solution at Point E?

Answer 4

5.19

Question 5

Look at the neutralization reaction for water.

Which statement about this reaction is not correct?

Answer 5

If you know the number of moles of OH − needed to neutralize a weak base, you can determine the number of moles of weak base that were consumed during the neutralization reaction.

Question 6

Look at the plot for the titration of a weak base, NH3, with a strong acid, HCl.

Which statement about this plot is not correct?

Answer 6

At Point D, we still have a significant amount of NH3 in solution.

Question 7

Look at the plot for the titration of a weak base, NH3, with a strong acid, HCl.

Suppose that we have 100.0 mL of 0.100 M NH3 titrated with 0.100 M HCl. At Point A, we have only NH3 in aqueous solution.

where Kb = 1.8 × 10−5

What is the pH of the solution at the initialization point Kw = 1.0 × 10−14?

Answer 7

11.13

Question 8

Look at the plot for the titration of a weak base, NH3, with a strong acid, HCl.

Which answer gives the range of all of the areas of the plot that are not buffered by NH3 (the weak base)?

Answer 8

C–H

Question 9

Look at the plot for the titration of a weak base, NH3, with a strong acid, HCl.

Which statement about this plot is not correct?

Answer 9

At Point G, the NH4+ and H + are contributing to the lowering of the pH value.

Question 10

What is the pH of the solution at Point H?

Assume that we started with 100.0 mL of 0.130 M NH3 titrated with 0.130 M HCl

Answer 10

1.4

Question 11

What is the pH of the solution at Point G?

Assume that we started with 100.0 mL of 0.160 M NH3 titrated with 0.160 M HCl.

Answer 11

1.85

Question 12

Use the plot to determine the change in pH between Points G and H.

Assume that we started with 100.0 mL of 0.140 M NH3 titrated with 0.140 M HCl.

Answer 12

0.477