AP - Advanced Placement Acids and Bases 1

Question 1

A 0.150 M solution of methylamine (CH₃NH₂) is prepared at 25°C. Given that Kb = 4.4 × 10⁻⁴ for methylamine, what is the pH of this solution?

Accepted Answer

11.90

Answer

2.10

Answer

11.18

Answer

12.66

Question 2

Which of the following species is amphiprotic?

Accepted Answer

HCO₃⁻

Answer

SO₄²⁻

Answer

NH₄⁺

Answer

CO₃²⁻

Question 3

A 0.050 M solution of a weak acid HA has a measured pH of 3.17 at 25°C. What is the percent dissociation of HA?

Accepted Answer

1.35%

Answer

6.34%

Answer

0.68%

Answer

3.17%

Question 4

For carbonic acid, Ka1 = 4.3 × 10⁻⁷ and Ka2 = 4.7 × 10⁻¹¹. Which statement best explains why Ka1 is approximately 10,000 times larger than Ka2?

Accepted Answer

The second proton must be removed from HCO₃⁻, which is already negatively charged, requiring greater energy to overcome the electrostatic attraction

Answer

H₂CO₃ has more hydrogen atoms available for donation than HCO₃⁻

Answer

CO₃²⁻ is a stronger base than HCO₃⁻, shifting equilibrium left

Answer

The O–H bond in HCO₃⁻ is longer and therefore weaker than in H₂CO₃

Question 5

A buffer solution has maximum resistance to pH change (maximum buffer capacity) when which condition is met?

Accepted Answer

The molar concentrations of weak acid and conjugate base are equal

Answer

The ratio [A⁻]/[HA] = 10

Answer

The concentration of the weak acid greatly exceeds the conjugate base concentration

Answer

The solution pH equals twice the pKa of the weak acid

Question 6

10.0 mL of 0.200 M HCl is diluted to a final volume of 500.0 mL with distilled water. What is the pH of the resulting solution?

Accepted Answer

2.40

Answer

1.70

Answer

3.10

Answer

2.70