Applications of Aqueous Equilibria

Practice flashcards covering key concepts related to aqueous equilibria, focusing on acid-base solutions, buffers, and titrations.

What happens to the pH when a conjugate base is added to a solution of a weak acid?

The pH will shift to a higher value.

How does the common ion effect influence the solubility of salts?

It shifts the chemical equilibrium to favor the formation of the solid salt, reducing its solubility.

What is a buffered solution?

A solution that resists changes in pH when small amounts of acids or bases are added.

What components make up an acid buffer?

A weak acid and a soluble salt of its conjugate base.

How do buffers maintain pH in biological systems, like human blood?

Buffers, through the common ion effect, stabilize pH by neutralizing added acids or bases.

What effect does adding H+ to a buffer solution have?

It reacts with the weak base component of the buffer, maintaining a relatively constant pH.

How can the pH of a buffered solution be calculated using the Henderson-Hasselbalch equation?

pH = pKa + log([A−]/[HA]), where [A−] is the concentration of the conjugate base and [HA] is the acid concentration.

What occurs at the equivalence point of a titration between a strong acid and a strong base?

The number of moles of acid equals the number of moles of base, resulting in a neutral solution (pH ">" 7).

In a titration curve, what does the steep part indicate?

It indicates a rapid change in pH with the addition of a small amount of titrant.

What effect does decreasing pH have on the solubility of insoluble bases?

Decreasing pH increases the solubility of insoluble bases.

How does the common ion effect change the molar solubility of a salt in solution?

The presence of a common ion reduces the molar solubility of the salt.

What is the purpose of using indicators in titrations?

Indicators are used to signal the end point of titrations by changing color.

What must be considered when choosing an indicator for a titration?

The pH range of the indicator should match the expected pH at the equivalence point.

What is the significance of a buffer's capacity?

Buffer capacity is the amount of acid or base the buffer can neutralize without a significant change in pH.

What is the relationship between pKa and the strength of an acid?

A lower pKa indicates a stronger acid.

Calculate the pH of a buffer solution if the pKa is 4.76, the concentration of the weak acid [HA] is 0.10 M, and the concentration of its conjugate base [A-] is 0.20 M.

Using the Henderson-Hasselbalch equation, pH = pKa + \log([A-]/[HA]), pH = 4.76 + \log(0.20/0.10) = 4.76 + \log(2.0) = 4.76 + 0.30 = 5.06. Therefore, pH = 5.06.

Calculate the pH of a buffer solution with a pKa of 5.20 if the concentration of the weak acid [HA] is 0.05 M and the concentration of its conjugate base [A-] is 0.15 M.

Using the Henderson-Hasselbalch equation, pH = pKa + \log([A-]/[HA]), pH = 5.20 + \log(0.15/0.05) = 5.20 + \log(3.0) \approx 5.20 + 0.477 = 5.677. Therefore, pH \approx 5.68.

How is the pKa value related to the acid dissociation constant (Ka)?

pKa = -\log(Ka)

If the Ka of an acid is 1.8 \times 10^{-5}, what is its pKa?

Using pKa = -\log(Ka), pKa = -\log(1.8 \times 10^{-5}) \approx 4.74.

If the pKa of an acid is 3.75, what is its acid dissociation constant (Ka)?

Using Ka = 10^{-pKa}, Ka = 10^{-3.75} \approx 1.78 \times 10^{-4}.

How do buffers resist changes in pH when a strong base is added?

The strong base (OH-) reacts with the weak acid component of the buffer, converting it into the conjugate base and water, thereby minimizing the change in pH.