Question 1

Calculate the pH of a solution formed by mixing 250.0 mL of 0.15 mol L^-1 NH₄Cl with 200.0 mL of 0.12 mol L^-1 NH₃. The K_b for NH₃ is 1.8 × 10^-5. A) 9.06 B) 9.45 C) 4.55 D) 4.74 E) 9.26

Accepted Answer

The correct answer is A because the pH of the solution is 9.06. The reaction between NH4Cl and NH3 is a weak acid-weak base reaction, and the pH of the solution will be determined by the equilibrium constant for the reaction. The equilibrium constant for the reaction is Kb = [NH4+][OH-]/[NH3], and the value of Kb is 1.8 × 10^-5. The concentration of NH4+ in the solution is 0.15 mol L^-1, and the concentration of NH3 in the solution is 0.12 mol L^-1. The concentration of OH- in the solution can be calculated using the equilibrium constant expression: [OH-] = Kb[NH3]/[NH4+] = (1.8 × 10^-5)(0.12 mol L^-1)/(0.15 mol L^-1) = 1.44 × 10^-5 mol L^-1. The pH of the solution can be calculated using the pOH: pOH = -log[OH-] = -log(1.44 × 10^-5 mol L^-1) = 4.84. The pH of the solution is 14 - pOH = 14 - 4.84 = 9.06.

Question 2

Calculate the pH of a solution formed by mixing 200.0 mL of 0.30 mol L^-1 HClO with 100.0 mL of 0.20 mol L^-1 KClO. The K_a for HClO is 2.9 × 10^-8. A) 5.99 B) 8.01 C) 7.54 D) 7.06 E) 6.46

Accepted Answer

D

Question 3

If the pK_a of HCOOH is 3.74 and the pH of an HCOOH/HCOONabuffer solution is 3.74, which of the following is TRUE? A) [HCOOH] > [HCOONa] B) [HCOOH] = [HCOONa] C) [HCOOH] < [HCOONa] D) [HCOOH] << [HCOONa] E) [HCOOH] >> [HCOONa]

Accepted Answer

When the pH of a buffer solution equals the pKa (or in this case, pK_a) of the weak acid, the concentration of the weak acid and its conjugate base are equal. Therefore, [HCOOH] = [HCOONa] in this buffer solution.

Question 4

Calculate the pH of a buffer that is 0.058 mol L^-1 HF and 0.058 mol L^-1 LiF. The K_a for HF is 3.5 × 10^-4. A) 2.86 B) 9.31 C) 10.54 D) 3.46 E) 4.69

Accepted Answer

The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]). Here, [A-] = [LiF] = 0.058 M and [HA] = [HF] = 0.058 M. The pKa is calculated as -log(Ka) = -log(3.5 × 10^-4) ≈ 3.46. Since the concentrations of the acid and its conjugate base are equal, the log term is zero, so pH = pKa = 3.46.

Question 5

Calculate the pH of a buffer that is 0.105 mol L^-1 CH₃COOH and 0.146 mol L^-1 CH₃COOK. The K_a for CH₃COOH is 1.8 × 10^-5. A) 4.89 B) 9.11 C) 4.74 D) 9.26 E) 4.60

Accepted Answer

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Question 6

Calculate the pH of a solution formed by mixing 100.0 mL of 0.20 mol L^-1 HClO with 200.0 mL of 0.30 mol L^-1 KClO. The K_a for HClO is 2.9 × 10^-8. A) 5.99 B) 8.01 C) 7.54 D) 7.06 E) 6.46

Accepted Answer

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Question 7

Calculate the pH of a buffer that is 0.040 mol L^-1 HF and 0.020 mol L^-1 LiF. The K_a for HF is 3.5 × 10^-4. A) 2.06 B) 4.86 C) 3.15 D) 3.46 E) 3.76

Accepted Answer

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Question 8

Which one of the following statements is TRUE?
A) A buffer is an aqueous solution composed of two weak acids.
B) A buffer can absorb an unlimited amount of acid or base.
C) A buffer resists pH change by neutralizing added acids and bases.
D) A buffer does not change pH when large amounts of a strong acid or a strong base are added.
E) The common ion in a buffer solution does not have any effect on the dissociation of the acidic component of the buffer solution.

Accepted Answer

A buffer solution resists pH change by neutralizing added acids or bases through its weak acid and its corresponding conjugate base or weak base and its corresponding conjugate acid. It can only absorb a limited amount of acid or base before the pH starts to change. Therefore, statement A, B, D, and E are false.

Question 9

Calculate the pH of a buffer that is 0.225 mol L^-1 CH₃COOH and 0.162 mol L^-1 CH₃COOK. The K_a for CH₃COOH is 1.8 × 10^-5. A) 4.89 B) 9.11 C) 4.74 D) 9.26 E) 4.60

Accepted Answer

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Question 10

If the pKa of HCOOH is 3.74 and the pH of an HCOOH/HCOONasolution is 3.11, which of the following is TRUE? A) [HCOOH] < [HCOONa] B) [HCOOH] = [HCOONa] C) [HCOOH] << [HCOONa] D) [HCOOH] > [HCOONa] E) [HCOOH] >> [HCOONa]

Accepted Answer

The pH of the solution (3.11) is lower than the pKa of HCOOH (3.74), which means that the solution is more acidic than the dissociation constant of HCOOH. This indicates that the majority of HCOOH molecules have dissociated into H+ ions and HCOO- ions. Since HCOONa is a salt of HCOO-, it will dissociate completely in solution, producing Na+ ions and HCOO- ions. Therefore, the concentration of HCOO- ions in the solution will be much higher than the concentration of undissociated HCOOH molecules. As a result, [HCOOH] > [HCOONa] is the correct answer, making option D the correct choice.

Question 11

Calculate the pH of a buffer that is 0.020 mol L^-1 HF and 0.040 mol L^-1 LiF. The K_a for HF is 3.5 × 10^-4. A) 2.06 B) 4.86 C) 3.16 D) 3.46 E) 3.76

Accepted Answer

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Question 12

You wish to prepare a buffer containing CH₃COOH with a pH of 5.44. If the pK_a of acetic acid is 4.74, what ratio of [CH₃COO⁻]/[CH₃COOH] must you use? A) 0.70 B) 0.20 C) 1.4 D) 5.0 E) 1.1

Accepted Answer

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Question 13

Calculate the pH of a buffer that is 0.158 mol L^-1 HClO and 0.099 mol L^-1 NaClO. The K_a for HClO is 2.9 × 10^-8. A) 7.54 B) 6.67 C) 3.77 D) 6.46 E) 7.33

Accepted Answer

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Question 14

You wish to prepare a buffer containing CH₃COOH with a pH of 4.24. If the pK_a of acetic acid is 4.74, what ratio of [CH₃COO⁻]/[CH₃COOH] must you use? A) 0.10 B) 0.50 C) 0.32 D) 2.0 E) 2.8

Accepted Answer

pH = pKa + log([A⁻]/[HA])

4.24 = 4.74 + log([A⁻]/[HA])

log([A⁻]/[HA]) = -0.5

[A⁻]/[HA] = antilog (-0.5)

[A⁻]/[HA] = 0.32

Therefore, the ratio of [CH3COO⁻]/[CH3COOH] to prepare the buffer with pH 4.24 is 0.32. Hence, the correct answer is C.

Question 15

Identify a good buffer.
A) a solution containing small amounts of both a weak acid and its conjugate base
B) a solution containing significant amounts of both a strong acid and a strong base
C) a solution containing small amounts of both a strong acid and a strong base
D) a solution containing significant amounts of both a weak acid and a strong acid
E) a solution containing significant amounts of both a weak acid and its conjugate base

Accepted Answer

A good buffer is a solution that contains significant amounts of both a weak acid and its conjugate base, allowing it to resist changes in pH when small amounts of acid or base are added.

Question 16

Calculate the pH of a solution formed by mixing 250.0 mL of 0.15 mol L^-1 NH₄Cl with 100.0 mL of 0.20 mol L^-1 NH₃. The K_b for NH₃ is 1.8 × 10^-5. A) 9.13 B) 9.25 C) 9.53 D) 4.74 E) 8.98

Accepted Answer

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Question 17

Which of the following solutions represents a good buffer system? A) a solution that is 0.10 mol L^-1 CH₃COOH and 0.10 mol L^-¹ CH₃COOLi B) a solution that is 0.10 mol L^-1 HF and 0.10 mol L^-1 CH₃COONa C) a solution that is 0.10 mol L^-1 HCl and 0.10 mol L^-1 NH₄⁺ D) a solution that is 0.10 mol L^-1 NaOH and 0.10 mol L^-1 KOH E) a solution that is 0.10 mol L^-1 HCl and 0.10 mol L^-1 KCl

Accepted Answer

A good buffer system consists of a weak acid and its conjugate base or a weak base and its conjugate acid. Option A has acetic acid (CH₃COOH) and its conjugate base (CH₃COO⁻ from CH₃COOLi), making it a suitable buffer system.

Question 18

A buffer solution is 0.100 mol L^-1 in both C₆H₅COOH and C₆H₅COOLi and has a pH of 4.19. Which of the following pH values would you expect after the addition of a small amount of a strong base? A) 3.89 B) 3.69 C) 5.69 D) 4.49 E) 8.89

Accepted Answer

A buffer solution resists changes in pH upon the addition of small amounts of acid or base. To determine the pH change after the addition of a strong base, we need to consider the components of the buffer solution and how they will react with the added base. The buffer solution contains both C₆H₅COOH (the acid) and C₆H₅COOLi (the salt of the acid). When a strong base is added, it will react with the acid in the buffer solution to form its conjugate base. The salt present in the buffer solution will then react with the added conjugate base to reform the original acid. The overall result is that the concentration of the acid and conjugate base in the buffer solution will remain relatively constant, and the pH of the solution will remain stable. Since the pH of the buffer solution is 4.19, we know that the concentration of H+ ions is 10^-4.19 = 6.49 x 10^-5 M. Because the buffer solution contains equal amounts of the acid and salt, we can assume that the initial concentration of the conjugate base is also 0.100 mol L^-1. When a strong base is added, it will react with the acid in the buffer solution to neutralize some of the H+ ions. This will shift the equilibrium towards the conjugate base, increasing its concentration. The concentration of the acid will decrease, but only slightly since it is present in excess in the buffer solution. The best choice among the answer options is D (4.49), as it is the only one close to the original pH of the buffer solution. The pH of the solution will increase slightly after the addition of the strong base, but it will still be within the acidic range. The exact pH change will depend on the amount of strong base added and the overall buffering capacity of the solution.

Question 19

Which of the following solutions is a good buffer system? A) a solution that is 0.10 mol L^-1 NaCl and 0.10 mol L^-1 HCl B) a solution that is 0.10 mol L^-1 HCN and 0.10 mol L^-1 LiCN C) a solution that is 0.10 mol L^-1 NaOH and 0.10 mol L^-1 HNO₃ D) a solution that is 0.10 mol L^-1 HNO₃ and 0.10 mol L^-1 KNO₃ E) a solution that is 0.10 mol L^-1 HCN and 0.10 mol L^-1 NaCl

Accepted Answer

A buffer system consists of a weak acid and its conjugate base or a weak base and its conjugate acid. Option B contains HCN, a weak acid, and LiCN, its conjugate base, making it a good buffer system. The other options contain either strong acids or bases, or do not have a weak acid/weak base conjugate pair.

Question 20

If the pK_aof HCOOH is 3.74 and the pH of an HCOOH/HCOONabuffer solution is 3.89, which of the following is TRUE? A) [HCOOH] < [HCOONa] B) [HCOOH] = [HCOONa] C) [HCOOH] > [HCOONa] D) [HCOOH] >> [HCOONa] E) [HCOOH] << [HCOONa]

Accepted Answer

The pH of the buffer solution is higher than the pKa, indicating that the concentration of the conjugate base (HCOONa) is greater than the concentration of the acid (HCOOH).

Quiz 16: Aqueous Ionic Equilibrium

Calculate the pH of a solution formed by mixing 250.0 mL of 0.15 mol L-1 NH4Cl with 200.0 mL of 0.12 mol L-1 NH3. The Kb for NH3 is 1.8 × 10-5.

Calculate the pH of a solution formed by mixing 200.0 mL of 0.30 mol L-1 HClO with 100.0 mL of 0.20 mol L-1 KClO. The Ka for HClO is 2.9 × 10-8.

If the pKa of HCOOH is 3.74 and the pH of an HCOOH/HCOONa buffer solution is 3.74, which of the following is TRUE?

Calculate the pH of a buffer that is 0.058 mol L-1 HF and 0.058 mol L-1 LiF. The Ka for HF is 3.5 × 10-4.

Calculate the pH of a buffer that is 0.105 mol L-1 CH3COOH and 0.146 mol L-1 CH3COOK. The Ka for CH3COOH is 1.8 × 10-5.

Calculate the pH of a solution formed by mixing 100.0 mL of 0.20 mol L-1 HClO with 200.0 mL of 0.30 mol L-1 KClO. The Ka for HClO is 2.9 × 10-8.

Calculate the pH of a buffer that is 0.040 mol L-1 HF and 0.020 mol L-1 LiF. The Ka for HF is 3.5 × 10-4.

Which one of the following statements is TRUE?

Calculate the pH of a buffer that is 0.225 mol L-1 CH3COOH and 0.162 mol L-1 CH3COOK. The Ka for CH3COOH is 1.8 × 10-5.

If the pKa of HCOOH is 3.74 and the pH of an HCOOH/HCOONa solution is 3.11, which of the following is TRUE?

Calculate the pH of a buffer that is 0.020 mol L-1 HF and 0.040 mol L-1 LiF. The Ka for HF is 3.5 × 10-4.

You wish to prepare a buffer containing CH3COOH with a pH of 5.44. If the pKa of acetic acid is 4.74, what ratio of [CH3COO⁻]/[CH3COOH] must you use?

Calculate the pH of a buffer that is 0.158 mol L-1 HClO and 0.099 mol L-1 NaClO. The Ka for HClO is 2.9 × 10-8.

You wish to prepare a buffer containing CH3COOH with a pH of 4.24. If the pKa of acetic acid is 4.74, what ratio of [CH3COO⁻]/[CH3COOH] must you use?

Identify a good buffer.

Calculate the pH of a solution formed by mixing 250.0 mL of 0.15 mol L-1 NH4Cl with 100.0 mL of 0.20 mol L-1 NH3. The Kb for NH3 is 1.8 × 10-5.

Which of the following solutions represents a good buffer system?

A buffer solution is 0.100 mol L-1 in both C6H5COOH and C6H5COOLi and has a pH of 4.19. Which of the following pH values would you expect after the addition of a small amount of a strong base?

Which of the following solutions is a good buffer system?

If the pKa of HCOOH is 3.74 and the pH of an HCOOH/HCOONa buffer solution is 3.89, which of the following is TRUE?

Calculate the pH of a solution formed by mixing 250.0 mL of 0.15 mol L^-1 NH₄Cl with 200.0 mL of 0.12 mol L^-1 NH₃. The K_b for NH₃ is 1.8 × 10^-5.

Calculate the pH of a solution formed by mixing 200.0 mL of 0.30 mol L^-1 HClO with 100.0 mL of 0.20 mol L^-1 KClO. The K_a for HClO is 2.9 × 10^-8.

If the pK_a of HCOOH is 3.74 and the pH of an HCOOH/HCOONabuffer solution is 3.74, which of the following is TRUE?

Calculate the pH of a buffer that is 0.058 mol L^-1 HF and 0.058 mol L^-1 LiF. The K_a for HF is 3.5 × 10^-4.

Calculate the pH of a buffer that is 0.105 mol L^-1 CH₃COOH and 0.146 mol L^-1 CH₃COOK. The K_a for CH₃COOH is 1.8 × 10^-5.

Calculate the pH of a solution formed by mixing 100.0 mL of 0.20 mol L^-1 HClO with 200.0 mL of 0.30 mol L^-1 KClO. The K_a for HClO is 2.9 × 10^-8.

Calculate the pH of a buffer that is 0.040 mol L^-1 HF and 0.020 mol L^-1 LiF. The K_a for HF is 3.5 × 10^-4.

Calculate the pH of a buffer that is 0.225 mol L^-1 CH₃COOH and 0.162 mol L^-1 CH₃COOK. The K_a for CH₃COOH is 1.8 × 10^-5.

If the pKa of HCOOH is 3.74 and the pH of an HCOOH/HCOONasolution is 3.11, which of the following is TRUE?

Calculate the pH of a buffer that is 0.020 mol L^-1 HF and 0.040 mol L^-1 LiF. The K_a for HF is 3.5 × 10^-4.

You wish to prepare a buffer containing CH₃COOH with a pH of 5.44. If the pK_a of acetic acid is 4.74, what ratio of [CH₃COO⁻]/[CH₃COOH] must you use?

Calculate the pH of a buffer that is 0.158 mol L^-1 HClO and 0.099 mol L^-1 NaClO. The K_a for HClO is 2.9 × 10^-8.

You wish to prepare a buffer containing CH₃COOH with a pH of 4.24. If the pK_a of acetic acid is 4.74, what ratio of [CH₃COO⁻]/[CH₃COOH] must you use?

Calculate the pH of a solution formed by mixing 250.0 mL of 0.15 mol L^-1 NH₄Cl with 100.0 mL of 0.20 mol L^-1 NH₃. The K_b for NH₃ is 1.8 × 10^-5.

A buffer solution is 0.100 mol L^-1 in both C₆H₅COOH and C₆H₅COOLi and has a pH of 4.19. Which of the following pH values would you expect after the addition of a small amount of a strong base?

If the pK_aof HCOOH is 3.74 and the pH of an HCOOH/HCOONabuffer solution is 3.89, which of the following is TRUE?