Acids, Bases & Titration — Chapter quiz · Physical Science: Chemistry, Grade 11

Separate strength from concentration and connect proton transfer with pH, buffers, and titration.

Problem 1

Which statement correctly describes a strong acid?
  1. It ionizes completely in water, releasing nearly all of its H⁺
  2. It always has a very high molarity
  3. It has a pH above 7
  4. It cannot conduct electricity in solution
Answer and explanation

It ionizes completely in water, releasing nearly all of its H⁺

A strong acid ionizes essentially completely, releasing almost all of its hydrogen ions into solution — a separate idea from how concentrated it is.

Problem 2

Explain the difference between a 'strong' acid and a 'concentrated' acid.
Answer and explanation

'Strong' describes how completely the acid ionizes in water — a strong acid ionizes almost 100%. 'Concentrated' describes how much acid is dissolved per liter (a high molarity). The two are independent: you can have a dilute solution of a strong acid or a concentrated solution of a weak acid.

Problem 3

A solution with a pH of 9 is…
  1. impossible
  2. strongly acidic
  3. neutral
  4. basic
Answer and explanation

basic

A pH above 7 is basic; 9 is above 7.

Problem 4

A solution has a hydrogen ion concentration [H⁺] of 1 × 10⁻³ M. What is its pH?
Answer and explanation

3

pH = −log(1 × 10⁻³) = 3.

Problem 5

How many times more acidic is a solution of pH 2 than a solution of pH 5?
Answer and explanation

1000 times

The pH values differ by 5 − 2 = 3 units, and each unit is a factor of 10, so the difference is 10³ = 1000 times.

Problem 6

Explain the following claim and supply a valid example or counterexample: Acid strength and concentration are independent; neither alone fixes pH.
Answer and explanation

It accepts a proton from water, forming NH₄⁺ and OH⁻; Brønsted bases need not contain hydroxide initially. Acid strength and concentration are independent; neither alone fixes pH.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 7

Independent chapter check: In NH₃+H₂O⇌NH₄⁺+OH⁻, identify the acid, base and both conjugate pairs. Explain why NH₃ can act as a base without OH in its formula.
Answer and explanation

H₂O donates a proton and NH₃ accepts it. Pairs are H₂O/OH⁻ and NH₄⁺/NH₃. NH₃ produces hydroxide through proton transfer with water rather than having to release pre-existing OH⁻ groups.

H₂O donates a proton and NH₃ accepts it. Pairs are H₂O/OH⁻ and NH₄⁺/NH₃. NH₃ produces hydroxide through proton transfer with water rather than having to release pre-existing OH⁻ groups.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 8

Explain the following claim and supply a valid example or counterexample: pH differences are logarithmic; neutrality near 7 assumes about 25°C.
Answer and explanation

pH3 has 10^(5−3)=100 times the hydronium concentration in the simple concentration model. pH differences are logarithmic; neutrality near 7 assumes about 25°C.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 9

Independent chapter check: Mix 20.0 mL 0.100 M strong monoprotic acid with 25.0 mL 0.100 M strong base at 25°C. Assume additive volumes and complete neutralization. Find approximate pH.
Answer and explanation

Acid=0.00200 mol and base=0.00250 mol, leaving 0.00050 mol OH⁻ in 0.0450 L. [OH⁻]≈0.0111 M, pOH≈1.95 and pH≈12.05. Do stoichiometry before logarithms.

Acid=0.00200 mol and base=0.00250 mol, leaving 0.00050 mol OH⁻ in 0.0450 L. [OH⁻]≈0.0111 M, pOH≈1.95 and pH≈12.05. Do stoichiometry before logarithms.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 10

Which acid is stronger in a comparable aqueous model: Ka=10⁻³ or 10⁻⁶?
Answer and explanation

Ka=10⁻³ implies more extensive ionization.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 11

Why check x/C after using the square-root approximation?
Answer and explanation

It checks whether replacing C−x by C changes the result appreciably.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 12

Independent chapter check: For a hypothetical monoprotic acid with C=0.200 M and Ka=2.0×10⁻⁵, estimate hydronium and pH, then test the small-ionization approximation.
Answer and explanation

x≈√(KaC)=√(4.0×10⁻⁶)=0.0020 M. pH≈2.70. x/C≈0.010=1%, supporting the approximation for ordinary classroom accuracy under the stated species model.

x≈√(KaC)=√(4.0×10⁻⁶)=0.0020 M. pH≈2.70. x/C≈0.010=1%, supporting the approximation for ordinary classroom accuracy under the stated species model.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 13

Differentiate endpoint and equivalence.
Answer and explanation

Endpoint is observed; equivalence is a stoichiometric condition. Their difference contributes systematic error.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 14

pKa=5 and conjugate-base/acid ratio=.1. Estimate pH.
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

4

log.1=−1, so 5−1=4.

Problem 15

Independent chapter check: A buffer initially has 0.080 mol HA and 0.120 mol A⁻, with pKa=4.80. Add 0.020 mol strong acid without exhausting either component. Estimate pH after reaction and state an approximation.
Answer and explanation

H⁺ converts A⁻ to HA, leaving 0.100 mol of each. The ratio is one, so pH≈4.80. Assume the usual dilute activity/concentration approximation with both conjugate components appreciable and a common final volume.

H⁺ converts A⁻ to HA, leaving 0.100 mol of each. The ratio is one, so pH≈4.80. Assume the usual dilute activity/concentration approximation with both conjugate components appreciable and a common final volume.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Browse all courses