Proton Transfer Reactions and Brønsted–Lowry Acids & Bases (IB Chemistry HL)

A comprehensive set of flashcards covering Brønsted–Lowry definitions, acid/base strength, conjugate pairs, buffers, pH concepts, titration points, and related equilibria.

What is a Brønsted–Lowry acid?

A Brønsted–Lowry acid is a species that donates a proton (H+).

What is a Brønsted–Lowry base?

A Brønsted–Lowry base is a species that accepts a proton (H+).

In the reaction HCl(aq) + H2O(l) → Cl-(aq) + H3O+(aq), which species acts as the acid?

HCl (aq) acts as the Brønsted–Lowry acid.

In the same reaction, which species acts as the base?

H2O(l) acts as the Brønsted–Lowry base.

Define amphiprotic.

Amphiprotic is a term describing species that can act both as proton donors and acceptors.

Is water an amphiprotic species?

Yes, water is amphiprotic (can donate or accept a proton).

True or False: All amphiprotic substances are amphoteric.

True.

True or False: All amphoteric substances are amphiprotic.

False (e.g., aluminium oxide is amphoteric but not amphiprotic).

What is a conjugate acid-base pair?

Two species that differ by a proton; the acid and its conjugate base.

What is the conjugate base of NH4+?

NH3.

What is the conjugate acid of NH3?

NH4+.

In CH3COOH + HCl ⇌ CH3COOH2+ + Cl-, what is the conjugate acid?

CH3COOH2+ is the conjugate acid.

Which acid is stronger: HI or HBr?

HI is the stronger acid.

Name some common strong acids.

HCl, HBr, HI, HNO3, and H2SO4.

Define a strong acid.

An acid that dissociates almost completely in aqueous solution.

Define a weak acid.

An acid that partially (incompletely) dissociates in aqueous solution.

Define a strong base.

A base that dissociates almost completely in aqueous solutions.

True or False: HCN is a strong acid when concentrated.

False. HCN is a weak acid even when concentrated.

What is the Ka of hydrocyanic acid (HCN)?

Ka ≈ 6.17 × 10^-10.

What is the pKa of hydrocyanic acid?

pKa ≈ 9.21.

What is the pKa of benzoic acid?

pKa ≈ 4.18.

What is the Ka of benzoic acid?

Ka ≈ 6.61 × 10^-5.

What is Kw?

Kw is the ion-product constant of water: Kw = [H+][OH-].

Does Kw change with temperature?

Yes, Kw changes as temperature changes.

What is the pH of a neutral solution at 298 K?

pH = 7.

Write the autoionization equation of water.

H2O(l) ⇌ H+(aq) + OH-(aq).

What is the relation between pH and pOH at a given temperature?

pH + pOH = pKw.

What is the pH of a solution with [H+] = 1.0 × 10^-3 M?

pH = 3.

What is the pH range for acidic solutions?

pH 0 to 6.

What is the pH range for alkaline solutions?

pH 8 to 14.

What is the most accurate method to measure pH?

Using a pH meter.

What is the pH at the equivalence point of a strong acid–strong base titration?

pH ≈ 7.

What is the half-equivalence point?

The point at which exactly half of the weak acid has been neutralised; pH = pKa at this point.

What region of a titration curve is labeled as the buffer region?

The region around the vertical section where the solution resists pH change (buffer region).

Define a buffer solution.

A solution that resists changes in pH upon addition of small amounts of acid or base.

What two components make up a typical acidic buffer?

A weak acid and its conjugate base (or a weak base and its conjugate acid).

What happens to pH when a buffer is diluted (ideal case)?

The pH remains largely unchanged if the ratio of acid to conjugate base stays constant.

What is the Henderson–Hasselbalch equation commonly used for?

Not explicitly given in the notes; (context: pH = pKa + log([A-]/[HA]); used for buffers.

Which indicator is suitable for a strong acid–weak base titration?

Methyl red.

Which indicator is suitable for a strong base–weak acid titration?

Phenolphthalein.

What is the equation for a neutralisation reaction?

Acid + base → salt + water.

What is the salt formed when sulfuric acid reacts with ammonia?

Ammonium sulfate (NH4)2SO4.

Is NaCl neutral in solution, and why?

Yes; Na+ and Cl- are spectator ions and do not affect pH.

What is the effect of adding OH- to an acidic buffer containing HA?

OH- reacts with H+ from HA to form H2O and shift equilibrium to re-establish HA.

What is the relation between Ka, Kb and Kw?

Ka × Kb = Kw.

What is the pKw value at 25°C?

pKw = 14 (at 25°C; temperature dependent in general).