IB Chemistry Quiz: Understand Proton Transfer Reactions

What this quiz covers

This quiz focuses on Understand Proton Transfer Reactions, giving you a quick way to practice the rules, question types, and explanations that matter most for IB Chemistry.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. H₂S and HCN
2. CN⁻ and HS⁻ (correct answer)
3. H₂S and HS⁻
4. CN⁻ and HCN

Question 2

1. H₃O⁺
2. HSO₄⁻ (correct answer)
3. SO₄²⁻
4. CH₃COOH

Question 3

1. 0.90 (correct answer)
2. 1.00
3. 1.10
4. 1.25

Question 4

1. It increases the concentration of hydroxide ions.
2. It is a molecule containing hydrogen atoms.
3. It accepts a proton from a water molecule. (correct answer)
4. It donates a lone pair of electrons to a proton.

Question 5

1. Acetate ions compete with water molecules for protons from $\text{NH}_4^+$, reducing the forward reaction rate and shifting equilibrium leftward.
2. Acetate ions accept protons from $\text{H}_3\text{O}^+$ ions, decreasing their concentration and shifting equilibrium leftward by Le Chatelier's principle. (correct answer)
3. Acetate ions donate protons to $\text{NH}_3$ molecules, converting them back to $\text{NH}_4^+$ and directly driving the reverse reaction.
4. Acetate ions form ion pairs with $\text{NH}_4^+$ ions, preventing them from participating in proton transfer and reducing system reactivity.

Question 6

1. 0.020 M, because the lower concentration of B limits the extent of proton transfer proportionally to the initial concentration ratio.
2. 0.035 M, because the equilibrium constant remains constant but the stoichiometry requires adjustment for the different initial concentrations. (correct answer)
3. 0.040 M, because the equilibrium constant ensures the same product concentrations regardless of different starting concentrations of reactants.
4. 0.057 M, because the higher HA concentration drives more complete proton transfer despite the lower B concentration limiting the reaction.

Question 7

1. When the solution pH is significantly above the $pK_a$ of the $\text{HPO}_4^{2-}/\text{PO}_4^{3-}$ conjugate acid-base pair, favoring deprotonation reactions. (correct answer)
2. When the solution pH is significantly below the $pK_a$ of the $\text{H}_2\text{PO}_4^-/\text{HPO}_4^{2-}$ conjugate acid-base pair, favoring the protonated form.
3. When strong acids are added to the solution, providing excess $\text{H}_3\text{O}^+$ ions that shift equilibrium toward proton donation by $\text{HPO}_4^{2-}$.
4. When the concentration of $\text{HPO}_4^{2-}$ exceeds the concentrations of both $\text{H}_2\text{PO}_4^-$ and $\text{PO}_4^{3-}$ in the solution.

Question 8

1. The initial concentration ratio of $\text{HClO}$ to $\text{ClO}^-$, since this determines the availability of reactants for each competing pathway.
2. The pH relative to the $pK_a$ of $\text{HClO}$, since this determines which species predominates and controls the reaction kinetics accordingly.
3. The equilibrium constants for both reactions, since the more thermodynamically favorable reaction will have the faster rate under buffer conditions.
4. The difference in activation energies between the forward neutralization reaction and the reverse hydrolysis reaction of the conjugate base. (correct answer)

Question 9

1. Methylamine is a stronger base than acetic acid is an acid, since the basic hydrolysis of $\text{CH}_3\text{NH}_3^+$ predominates over acidic hydrolysis of $\text{CH}_3\text{COO}^-$. (correct answer)
2. Acetic acid is a stronger acid than methylamine is a base, since the solution pH is above 7 due to incomplete neutralization leaving excess acid.
3. The base and acid have equal strengths since they react in a 1:1 molar ratio and produce equal amounts of conjugate species.
4. Acetic acid is a weaker acid than methylamine is a base, since the acidic hydrolysis of $\text{CH}_3\text{COO}^-$ is less significant than basic hydrolysis of $\text{CH}_3\text{NH}_3^+$.

Question 10

1. $\text{NH}_3$ is a much stronger base than $\text{PO}_4^{3-}$ since the equilibrium lies far to the left, favoring the weaker base remaining protonated.
2. $\text{PO}_4^{3-}$ is a much stronger base than $\text{NH}_3$ since the small equilibrium constant indicates the stronger base preferentially retains protons.
3. $\text{PO}_4^{3-}$ is a much stronger base than $\text{NH}_3$ since the equilibrium lies far to the left, favoring the stronger base in its protonated form. (correct answer)
4. The relative base strengths cannot be determined from this equilibrium constant since the reaction involves multiple proton transfers with different stoichiometry.

Question 11

1. The reaction is thermodynamically unfavorable, requiring multiple collision attempts before successful proton transfer occurs between the reactant species.
2. The reaction involves a pre-equilibrium formation of hydrogen-bonded complexes that must rearrange before the actual proton transfer step.
3. The reaction is diffusion-controlled, with essentially every collision between HCN and $\text{OH}^-$ resulting in immediate and successful proton transfer. (correct answer)
4. The reaction requires specific molecular orientations during collision, making the geometric probability factor the primary determinant of reaction rate.

Question 12

1. The forward reaction involves neutral HA molecules whose reactivity is unaffected by solution pH, while the reverse reaction requires collisions between charged species whose concentrations vary with pH.
2. The forward reaction involves intramolecular proton transfer that is pH-independent, while the reverse reaction involves intermolecular proton transfer that becomes more favorable at higher pH.
3. The forward reaction rate depends only on [HA] which is buffered and constant, while the reverse reaction rate depends on both [$\text{H}_3\text{O}^+$] and [$\text{A}^-$] which change with pH.
4. The forward reaction has a pH-independent activation energy since it involves breaking the same H-A bond regardless of conditions, while the reverse reaction activation energy decreases with increasing pH. (correct answer)

Question 13

1. The equilibrium lies far to the right because HF is a stronger acid than $\text{HSO}_4^-$ and will preferentially donate protons to $\text{SO}_4^{2-}$.
2. The equilibrium lies significantly to the left because $\text{HSO}_4^-$ is a stronger acid than HF and the reverse reaction is favored. (correct answer)
3. The equilibrium lies close to the center because the difference in acid strengths is moderate, resulting in comparable forward and reverse rates.
4. The equilibrium position cannot be determined from the given data because it depends on the relative concentrations of all four species.

Question 14

1. H₂PO₄⁻
2. H₂O
3. NH₄⁺
4. CO₃²⁻ (correct answer)

Question 15

1. 1.0
2. 2.0
3. 3.0 (correct answer)
4. 4.0

Question 16

1. 1.30
2. 7.00
3. 12.70 (correct answer)
4. 13.00

Question 17

1. 2.0 × 10⁻¹³ (correct answer)
2. 5.0 × 10⁻¹³
3. 5.0 × 10⁻¹²
4. 1.0 × 10⁻⁷

Question 18

1. CH₃COOH(aq), Na⁺(aq), and OH⁻(aq)
2. CH₃COO⁻(aq) and Na⁺(aq) (correct answer)
3. CH₃COOH(aq), CH₃COO⁻(aq), and Na⁺(aq)
4. H⁺(aq), OH⁻(aq), Na⁺(aq), and CH₃COO⁻(aq)

Question 19

1. 1.50
2. 1.72 (correct answer)
3. 2.00
4. 2.72

Question 20

1. CN⁻ is a stronger base than Cl⁻. (correct answer)
2. Cl⁻ is a stronger base than CN⁻.
3. Both Cl⁻ and CN⁻ are strong bases.
4. Both Cl⁻ and CN⁻ have negligible basic properties.