Ap chem 프린스턴 화학 summary part 8

Use the following information to answer questions 1–5.

A student titrates 20.0 mL of 1.0 M NaOH with 2.0 M formic acid, HCO₂H (K_a = 1.8 × 10^-4). Formic acid is a monoprotic acid.

Question 1:

A solution of 0.10 M sodium hydroxide (NaOH) is being titrated into 20.0 mL of formic acid (HCOOH) of unknown concentration. It takes 10.0 mL of the NaOH solution to reach the equivalence point. What is the concentration of the formic acid solution?

Options:

• (A) 0.050 M
• (B) 0.100 M
• (C) 0.200 M
• (D) 0.500 M

Question 2:

At the equivalence point, is the solution acidic, basic, or neutral? Why?

Options:

• (A) Acidic; the strong acid dissociates more than the weak base
• (B) Basic; the only acidic or basic ion present at equilibrium is the conjugate base
• (C) Basic; the higher concentration of the base is the determining factor
• (D) Neutral; equal moles of both acid and base are present

Question 3:

If the formic acid were replaced with a strong acid such as HCl at the same concentration (2.0 M), how would that change the volume needed to reach the equivalence point?

Options:

• (A) The change would reduce the amount, as the acid now fully dissociates
• (B) The change would reduce the amount, because the base will be more strongly attracted to the acid.
• (C) The change would increase the amount, because the reaction will now go to completion instead of equilibrium
• (D) Changing the strength of the acid will not change the volume needed to reach equivalence.

Question 4:

Which of the following would create a good buffer when dissolved in formic acid?

Options:

• (A) HCOONa
• (B) HC₂H₃O₂
• (C) NH₃
• (D) H₂O

Question 5:

The equation CH₃NH₂(aq) + H₂O(l) ⇌ CH₃NH₃⁺(aq) + OH^-(aq) represents the reaction between the weak base methylamine and water. Which of the following best represents the concentrations of the various species at equilibrium?

Options:

• (A) [CH₃NH₂] > [CH₃NH₃⁺] = [OH^-]
• (B) [OH^-] > [CH₃NH₂] > [CH₃NH₃⁺]
• (C) [CH₃NH₃⁺] = [OH^-] > [CH₃NH₂]
• (D) [CH₃NH₂] = [CH₃NH₃⁺] = [OH^-]

Question 6:

A 0.1-molar solution of which of the following acids will be the best conductor of electricity?

Options:

• (A) H₂CO₃
• (B) H₂S
• (C) HF
• (D) HNO₃

Question 7:

A laboratory technician wishes to create a buffered solution with a pH of 5. Which of the following acids would be the best choice for the buffer?

Options:

• (A) Oxalic acid (H₂C₂O₄), K_a = 5.9 × 10^-2
• (B) Arsenic acid (H₃AsO₄), K_a = 5.6 × 10^-3
• (C) Acetic acid (HC₂H₃O₂), K_a = 1.8 × 10^-5
• (D) Hypochlorous acid (HOCl), K_a = 3.0 × 10^-8

Question 8:

A solution of sulfurous acid (H₂SO₃) is present in an aqueous solution. Which of the following represents the relative concentrations of the different species in solution?

Options:

• (A) [SO₃^2-] > [HSO₃^-] > [H₂SO₃]
• (B) [H₂SO₃] > [HSO₃^-] > [SO₃^2-]
• (C) [HSO₃^-] > [H₂SO₃] = [SO₃^2-]
• (D) [SO₃^2-] = [HSO₃^-] > [H₂SO₃]

Question 9:

What is the pH of a buffer solution made by combining 0.50 moles of acetic acid (CH₃COOH) and 0.25 moles of sodium acetate (CH₃COONa) in 1.0 L of water? The K_a of acetic acid is 1.8 × 10^-5.

Options:

• (A) 4.44
• (B) 4.14
• (C) 4.74
• (D) 5.00

Question 10:

What is the pH of a 0.010 M solution of formic acid (HCOOH)? The K_a of formic acid is 1.8 × 10^-4.

Options:

• (A) 3.18
• (B) 2.74
• (C) 2.90
• (D) 3.74

Question 11:

Which of the following indicators would be best for a titration where the endpoint pH is expected to be around 9.5?

Options:

• (A) Bromothymol blue (pH range: 6.0 - 7.6)
• (B) Phenolphthalein (pH range: 8.3 - 10.0)
• (C) Methyl orange (pH range: 3.1 - 4.4)
• (D) Litmus (pH range: 4.5 - 8.3)

Question 12:

An aqueous solution of NH₄Cl is mildly acidic. Which of the following statements explains this observation?

Options:

• (A) The NH₄⁺ ion reacts with water to produce H₃O⁺, lowering the pH.
• (B) The Cl^- ion reacts with water to produce HCl, lowering the pH.
• (C) Both NH₄⁺ and Cl^- ions hydrolyze water to produce an acidic solution.
• (D) NH₄Cl is the salt of a strong base and strong acid, which makes its solution acidic.

Question 13:

An aqueous solution of sodium acetate (NaC₂H₃O₂) is basic. What is the best explanation for this?

Options:

• (A) The acetate ion (C₂H₃O₂^-) reacts with water to produce OH^-, raising the pH.
• (B) The Na⁺ ion reacts with water to produce NaOH, raising the pH.
• (C) Sodium acetate is the salt of a strong base and strong acid, making the solution basic.
• (D) Both Na⁺ and C₂H₃O₂^- ions hydrolyze to produce a basic solution.

Question 14:

Which of the following salts, when dissolved in water, produces a neutral (pH ≈ 7) solution?

Options:

• (A) NaCl
• (B) NH₄Cl
• (C) Na₂CO₃
• (D) CH₃COONa

Question 15:

Which of the following pairs of substances, when mixed in solution, would produce a buffer solution?

Options:

• (A) HCl and NaCl (equal volumes)
• (B) CH₃COOH and CH₃COONa (equal concentrations)
• (C) HNO₃ and NaNO₃ (equal moles)
• (D) NaOH and KCl (equal moles)

Question 16:

A buffer solution contains appreciable amounts of acetic acid (CH₃COOH) and sodium acetate (CH₃COONa). Which equation best represents what happens when a small amount of NaOH is added to this buffer?

Options:

• (A) CH₃COOH + OH^- → CH₃COO^- + H₂O
• (B) CH₃COO^- + OH^- → CH₃COOH + O^2-
• (C) CH₃COOH + H⁺ → CH₃COOH₂⁺
• (D) CH₃COO^- + H⁺ → CH₃COOH

Question 17:

During the titration of a weak acid with a strong base, the half-equivalence point is reached when half of the acid has been neutralized. Which of the following is true at the half-equivalence point?

Options:

• (A) pH = pK_a of the acid (and [HA] = [A^-]).
• (B) pH = 7.00 for any weak acid titration.
• (C) The moles of base added are equal to the initial moles of acid.
• (D) The buffering capacity of the solution is effectively zero.

Question 18:

In a buffer solution, if the pH is greater than the pK_a of the weak acid, which of the following statements is true about the concentrations of the conjugate base [A^-] and the acid [HA]?

Options:

• (A) [A^-] > [HA]
• (B) [A^-] = [HA]
• (C) [A^-] < [HA]
• (D) No relationship can be determined from the pH and pK_a.

Question 19:

What is the percent dissociation of 0.020 M formic acid (HCOOH)? (K_a = 1.8 × 10^-4)

Options:

• (A) ~3.0%
• (B) ~6.0%
• (C) ~9.5%
• (D) ~19%

Question 20:

Estimate the percent dissociation of 0.010 M hydrofluoric acid (HF). (K_a = 6.8 × 10^-4)

Options:

• (A) ~8%
• (B) ~14%
• (C) ~26%
• (D) ~2.6%

Question 21:

A 0.10 M solution of formic acid (HCOOH) is prepared. Which change will decrease its percent dissociation the most?

Options:

• (A) Diluting the solution to 0.010 M
• (B) Adding solid NaCl
• (C) Adding 0.10 M NaHCOO (sodium formate)
• (D) Warming the solution by 5 °C

Question 22:

A 0.10 M acetic acid (CH₃COOH) solution has a percent dissociation of about 1.3%. If this solution is diluted tenfold to 0.010 M (same K_a), the percent dissociation will:

Options:

• (A) Stay the same
• (B) Approximately double
• (C) Increase by a factor of about √10 (≈ 3.16)
• (D) Decrease by a factor of about √10 (≈ 0.32)

Question 23:

What is the approximate percent dissociation of 0.050 M benzoic acid (C₆H₅COOH)? (K_a = 6.3 × 10^-5)

Options:

• (A) ~1.1%
• (B) ~2.2%
• (C) ~3.6%
• (D) ~7.2%

Question 24:

What is the pH of a 0.10 M NH₄Cl solution at 25 °C? (K_b for NH₃ = 1.8 × 10^-5)

Options:

• (A) 5.13
• (B) 6.50
• (C) 7.00
• (D) 8.87

Question 25:

What is the pH of a 0.10 M CH₃COONa solution at 25 °C? (K_a for CH₃COOH = 1.8 × 10^-5)

Options:

• (A) 5.13
• (B) 8.87
• (C) 7.00
• (D) 6.50

Question 26:

A weak acid HA (pK_a = 3.17) is titrated with a strong base. What is the pH at the half-equivalence point?

Options:

• (A) 3.17
• (B) 7.00
• (C) 2.00
• (D) 4.74

Question 27:

Mix 100.0 mL of 0.200 M CH₃COOH with 50.0 mL of 0.100 M NaOH. What is the resulting pH? (pK_a of CH₃COOH = 4.74)

Options:

• (A) 4.26
• (B) 4.74
• (C) 5.21
• (D) 3.74

Question 28:

Which indicator is most suitable for a titration of a weak base with a strong acid if the expected endpoint pH is ~5.0?

Options:

• (A) Phenolphthalein (8.3–10.0)
• (B) Methyl orange (3.1–4.4)
• (C) Methyl red (4.4–6.2)
• (D) Bromothymol blue (6.0–7.6)

Question 29:

A buffer contains 0.20 M HA and 0.40 M A^- (pK_a = 4.74). What is the pH?

Options:

• (A) 4.44
• (B) 5.04
• (C) 4.74
• (D) 5.44

Question 30:

Which change increases the percent dissociation of a weak acid HA the most?

Options:

• (A) Adding its conjugate base salt (A^-)
• (B) Diluting the solution
• (C) Adding a neutral salt (e.g., NaCl)
• (D) Slightly increasing temperature (assume endothermic dissociation is negligible)

Question 31:

What is the pH of a buffer solution made by combining 0.50 moles of acetic acid (CH₃COOH) and 0.25 moles of sodium acetate (CH₃COONa) in 1.0 L of water? The K_a of acetic acid is 1.8 × 10^-5.

Options:

• (A) 4.44
• (B) 4.14
• (C) 4.74
• (D) 5.00

Answer Explanation:
Use the Henderson-Hasselbalch equation for buffer solutions:
pH = pKa + log([conjugate base]/[acid]) 
First, calculate the pKa:
pKa = −log(1.8 × 10−5) = 4.74 
Now, substitute the concentrations into the equation:
pH = 4.74 + log(0.25/0.50) = 4.74 + log(0.50) = 4.74 − 0.30 = 4.44 
Correct Answer: (A)

Question 32:

What is the pH of a 0.010 M solution of formic acid (HCOOH)? The K_a of formic acid is 1.8 × 10^-4.

Options:

• (A) 3.18
• (B) 2.74
• (C) 2.90
• (D) 3.74

Answer Explanation:
Use the Ka expression for formic acid: 
Ka = [H+][A-]/[HA] = x2/(0.010 − x) = 1.8 × 10−4 
In this case, the dissociation is significant (>5%), so we should use the quadratic formula to solve for x = [H+]: 
x2 + (1.8 × 10−4)x − (1.8 × 10−6) = 0 
Solving for x gives:
x = 1.255 × 10−3 M
The pH is:
pH = −log(1.255 × 10−3) = 2.90
Correct Answer: (C)

Question 33:

What is the pH of a buffer solution containing 0.10 M of lactic acid (C₃H₆O₃) and 0.05 M of sodium lactate (C₃H₅O₃Na)? The K_a of lactic acid is 1.4 × 10^-4.

Options:

• (A) 3.08
• (B) 3.24
• (C) 3.55
• (D) 3.00

Answer Explanation:
Use the Henderson-Hasselbalch equation:
pH = pKa + log([conjugate base]/[acid]) 
Calculate pKa:
pKa = −log(1.4 × 10−4) = 3.85 
Substitute the concentrations into the equation:
pH = 3.85 + log(0.05/0.10) = 3.85 + log(0.50) = 3.85 − 0.30 = 3.55 
Correct Answer: (C)

Question 34:

A buffer solution is prepared by dissolving 0.40 moles of sodium hydrogen carbonate (NaHCO₃) in 1.0 L of 0.50 M carbonic acid (H₂CO₃). What is the pH of the solution? The K_a of carbonic acid is 4.3 × 10^-7.

Options:

• (A) 6.12
• (B) 6.27
• (C) 6.50
• (D) 6.74

Answer Explanation:
Use the Henderson-Hasselbalch equation:
pH = pKa + log([conjugate base]/[acid]) 
Calculate pKa:
pKa = −log(4.3 × 10−7) = 6.37 
Substitute the concentrations into the equation:
pH = 6.37 + log(0.40/0.50) = 6.37 + log(0.80) = 6.37 − 0.10 = 6.27 
Correct Answer: (B)

Question 35:

What is the pH of a 0.20 M solution of sodium hydroxide (NaOH)?

Options:

• (A) 13.30
• (B) 13.60
• (C) 12.60
• (D) 13.00

Answer Explanation:
For a strong base like NaOH, the concentration of OH⁻ ions is equal to the NaOH concentration. Calculate the pOH:
pOH=− log(0.20)=0.70
Now, calculate the pH:
pH=14−pOH=14−0.70=13.30
Correct Answer: (A)

Question 36:

What is the pH of a solution that contains 0.10 M HCO₃^- and 0.05 M H₂CO₃? The K_a of carbonic acid is 4.3 × 10^-7.

Options:

• (A) 6.54
• (B) 6.37
• (C) 6.67
• (D) 6.20

Answer Explanation:
Using the Henderson-Hasselbalch equation:
pH = pKa + log([conjugate base]/[acid]) 
Calculate pKa:
pKa = − log(4.3 × 10−7) = 6.37 
Substitute the concentrations into the equation:
pH = 6.37 + log(0.10/0.05) = 6.37 + log(2.00) = 6.37 + 0.30 = 6.67 
Correct Answer: (C)

Question 37: Which of the following is a strong acid?

• (A) HCl
• (B) HF
• (C) H₂CO₃
• (D) H₃PO₄

Correct Answer: (A) Hydrochloric acid (HCl) is a strong acid that completely dissociates in water.

Question 38: Which of the following pairs can form a buffer solution?

• (A) HCl and NaCl
• (B) NH₃ and NH₄Cl
• (C) H₂SO₄ and Na₂SO₄
• (D) NaOH and KOH

Correct Answer: (B) This pair forms a buffer solution as NH₃ is a weak base and NH₄Cl contains its conjugate acid.

Question 39: Which of the following is a weak acid?

• (A) HNO₃
• (B) CH₃COOH
• (C) H₂SO₄
• (D) HI

Correct Answer: (B) Acetic acid (CH₃COOH) is a weak acid because it only partially dissociates in water.

Question 40: Which of the following salts will produce a basic solution when dissolved in water?

• (A) NaCl
• (B) NH₄Cl
• (C) KNO₃
• (D) Na₂CO₃

Correct Answer: (D) Sodium carbonate (Na₂CO₃) is a salt that will produce a basic solution because the carbonate ion (CO₃²⁻) is a weak base.

Question 41: Identify the strong base among the following compounds.

• (A) NH₃
• (B) NaOH
• (C) Al(OH)₃
• (D) Mg(OH)₂

Correct Answer: (B) Sodium hydroxide (NaOH) is a strong base that fully dissociates in water.

Question 42: During the titration of 25.0 mL of 0.1 M acetic acid (CH₃COOH) with 0.1 M NaOH, what is the pH at the equivalence point?

• (A) 7.00
• (B) 8.72
• (C) 4.74
• (D) 3.00

Correct Answer: (B) At the equivalence point, the solution contains the conjugate base (CH₃COO⁻), which makes the solution basic.

Question 43: Which of the following is a weak base?

• (A) KOH
• (B) NH₃
• (C) Ca(OH)₂
• (D) LiOH

Correct Answer: (B) Ammonia (NH₃) is a weak base because it only partially dissociates in water.

Question 44: Which of the following solutions would best resist a pH change when a small amount of HCl is added?

• (A) HCl and NaCl
• (B) CH₃COOH and CH₃COONa
• (C) NaOH and KOH
• (D) H₂SO₄ and Na₂SO₄

Correct Answer: (B) This is a buffer solution that resists pH changes when a small amount of acid or base is added.

Question 45: Which of the following acids is strong?

• (A) HClO₄
• (B) H₃PO₄
• (C) H₂CO₃
• (D) CH₃COOH

Correct Answer: (A) Perchloric acid (HClO₄) is a strong acid and completely dissociates in water.

Question 46: Which of the following salts will produce an acidic solution when dissolved in water?

• (A) NaCl
• (B) NH₄NO₃
• (C) KNO₃
• (D) CaCl₂

Correct Answer: (B) Ammonium nitrate (NH₄NO₃) produces an acidic solution due to the presence of NH₄⁺, which is a weak acid.

Question 47: Select the weak acid among the following options.

• (A) HNO₃
• (B) HCl
• (C) H₂SO₄
• (D) H₂CO₃

Correct Answer: (D) Carbonic acid (H₂CO₃) is a weak acid because it only partially dissociates in water.

Question 48: What is the pH at the halfway point in the titration of 50 mL of 0.1 M acetic acid with 0.1 M NaOH?

• (A) 4.74
• (B) 7.00
• (C) 5.00
• (D) 3.00

Correct Answer: (A) At the halfway point, the pH is equal to the pKa of the acid. The pKa of acetic acid is 4.74.

Question 49: Which of the following is a strong base?

• (A) NaOH
• (B) NH₄OH
• (C) Al(OH)₃
• (D) CH₃NH₂

Correct Answer: (A) Sodium hydroxide (NaOH) is a strong base and dissociates completely in water.

Question 50: A buffer solution has a pH of 5.0. Which of the following acids would be best for creating this buffer?

• (A) Acetic acid, pKa = 4.74
• (B) Formic acid, pKa = 3.75
• (C) Hydrochloric acid, pKa < 0
• (D) Nitric acid, pKa < 0

Correct Answer: (A) The pKa of acetic acid (4.74) is close to the desired pH of 5.0, making it suitable for the buffer.

Question 51: Identify the weak base in this list.

• (A) KOH
• (B) Ca(OH)₂
• (C) NH₃
• (D) Ba(OH)₂

Correct Answer: (C) Ammonia (NH₃) is a weak base as it only partially dissociates in water.

Question 52: Which salt, when dissolved in water, would likely produce a solution with a pH greater than 7?

• (A) NaCl
• (B) NH₄Cl
• (C) KNO₃
• (D) Na₂CO₃

Correct Answer: (D) Sodium carbonate (Na₂CO₃) forms a basic solution as the carbonate ion (CO₃²⁻) is a weak base.

Question 53: Which of the following is a strong acid?

• (A) HClO₃
• (B) H₂CO₃
• (C) HF
• (D) CH₃COOH

Correct Answer: (A) Chloric acid (HClO₃) is a strong acid and dissociates completely in water.

Question 54: Which of the following is a strong acid?

• (A) HBr
• (B) CH₃COOH
• (C) H₂CO₃
• (D) H₃PO₄

Correct Answer: (A) Hydrobromic acid (HBr) is a strong acid that fully dissociates in water.

Question 55: Which indicator would be most suitable for a titration between a strong acid and a strong base?

• (A) Methyl orange (pH range: 3.1 - 4.4)
• (B) Phenolphthalein (pH range: 8.3 - 10.0)
• (C) Bromothymol blue (pH range: 6.0 - 7.6)
• (D) Thymol blue (pH range: 1.2 - 2.8)

Correct Answer: (C) Bromothymol blue is suitable for strong acid-strong base titrations as it changes color around the neutral pH range.

Question 56: Which of the following salts will produce an acidic solution when dissolved in water?

• (A) Na₂SO₄
• (B) NH₄NO₃
• (C) KCl
• (D) CaCl₂

Correct Answer: (B) Ammonium nitrate (NH₄NO₃) produces an acidic solution due to the presence of NH₄⁺, which is a weak acid.

Question 57: Which of the following would not form a buffer solution?

• (A) CH₃COOH and CH₃COONa
• (B) HCl and NaCl
• (C) NH₃ and NH₄Cl
• (D) H₂CO₃ and NaHCO₃

Correct Answer: (B) This combination does not form a buffer as HCl is a strong acid and does not have a weak conjugate base in this pair.

Question 58: In the titration of a weak acid with a strong base, which indicator would be most appropriate?

• (A) Methyl red (pH range: 4.4 - 6.2)
• (B) Bromothymol blue (pH range: 6.0 - 7.6)
• (C) Phenolphthalein (pH range: 8.3 - 10.0)
• (D) Thymol blue (pH range: 1.2 - 2.8)

Correct Answer: (C) For weak acid-strong base titrations, phenolphthalein is suitable as the pH at the equivalence point is usually above 7.

Question 59: Which of the following acids is considered weak?

• (A) HNO₃
• (B) HF
• (C) HCl
• (D) H₂SO₄

Correct Answer: (B) Hydrofluoric acid (HF) is a weak acid as it only partially dissociates in water.

Question 60: Which of the following indicators would change color at a pH of approximately 5.5?

• (A) Methyl orange (pH range: 3.1 - 4.4)
• (B) Bromothymol blue (pH range: 6.0 - 7.6)
• (C) Methyl red (pH range: 4.4 - 6.2)
• (D) Phenolphthalein (pH range: 8.3 - 10.0)

Correct Answer: (C) Methyl red changes color in the pH range 4.4 to 6.2, covering pH 5.5.

Question 61: Which of the following is a strong base?

• (A) NH₃
• (B) KOH
• (C) CH₃NH₂
• (D) Al(OH)₃

Correct Answer: (B) Potassium hydroxide (KOH) is a strong base that fully dissociates in water.

Question 62: Which of the following buffer solutions would have the highest pH?

• (A) CH₃COOH and CH₃COONa
• (B) H₂CO₃ and NaHCO₃
• (C) NH₄Cl and NH₃
• (D) H₃PO₄ and NaH₂PO₄

Correct Answer: (C) This buffer is made from a weak base (NH₃) and its conjugate acid, so its buffering range is in the basic pH region (around 9.25), which is higher than the acidic buffers listed.

Question 63: In a titration of a strong base with a weak acid, the pH at the equivalence point is likely to be:

• (A) 7.0
• (B) Less than 7.0
• (C) Greater than 7.0
• (D) Depends on the initial concentration

Correct Answer: (C) At the equivalence point, the weak acid has been converted to its conjugate base, which makes the solution basic (pH > 7).

Question 64: Which indicator would be best for detecting the endpoint in a titration involving a weak base and a strong acid?

• (A) Phenolphthalein (pH range: 8.3 - 10.0)
• (B) Bromophenol blue (pH range: 3.0 - 4.6)
• (C) Bromothymol blue (pH range: 6.0 - 7.6)
• (D) Methyl orange (pH range: 3.1 - 4.4)

Correct Answer: (D) For a weak base-strong acid titration, the pH at the equivalence point is acidic (pH < 7). An indicator like methyl orange is suitable because its color change range is in the acidic region.

Question 65: A buffer solution is made with 0.1 M acetic acid (CH₃COOH) and 0.1 M sodium acetate (CH₃COONa). What is the pH of the buffer if the pKa of acetic acid is 4.74?

• (A) 4.74
• (B) 5.00
• (C) 4.50
• (D) 7.00

Correct Answer: (A) When the concentrations of the weak acid and its conjugate base are equal, the pH of the buffer is equal to the pKa.

Question 66: When sodium acetate (CH₃COONa) dissolves in water, the resulting solution will be:

• (A) Acidic
• (B) Basic
• (C) Neutral
• (D) Depends on concentration

Correct Answer: (B) Acetate (CH₃COO⁻) is the conjugate base of a weak acid and will hydrolyze water to form a basic solution.

Question 67: Which of the following indicators would be best for a titration where the endpoint pH is expected to be around 9.5?

• (A) Bromothymol blue (pH range: 6.0 - 7.6)
• (B) Phenolphthalein (pH range: 8.3 - 10.0)
• (C) Methyl orange (pH range: 3.1 - 4.4)
• (D) Litmus (pH range: 4.5 - 8.3)

Correct Answer: (B) Phenolphthalein changes color in the range of 8.3 to 10.0, which is perfect for detecting an endpoint around pH 9.5.

Question 68:

An aqueous solution of NH₄Cl is mildly acidic. Which of the following statements explains this observation?

Options:

• (A) The NH₄⁺ ion reacts with water to produce H₃O⁺, lowering the pH.
• (B) The Cl^- ion reacts with water to produce HCl, lowering the pH.
• (C) Both NH₄⁺ and Cl^- ions hydrolyze water to produce an acidic solution.
• (D) NH₄Cl is the salt of a strong base and strong acid, which makes its solution acidic.

Question 69:

An aqueous solution of sodium acetate (NaC₂H₃O₂) is basic. What is the best explanation for this?

Options:

• (A) The acetate ion (C₂H₃O₂^-) reacts with water to produce OH^-, raising the pH.
• (B) The Na⁺ ion reacts with water to produce NaOH, raising the pH.
• (C) Sodium acetate is the salt of a strong base and strong acid, making the solution basic.
• (D) Both Na⁺ and C₂H₃O₂^- ions hydrolyze to produce a basic solution.

Question 70:

Which of the following salts, when dissolved in water, produces a neutral (pH ≈ 7) solution?

Options:

• (A) NaCl
• (B) NH₄Cl
• (C) Na₂CO₃
• (D) CH₃COONa