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IB Diploma Chemistry SL · Reactivity 3.1 — proton transfer reactions
Mini-Lesson

Proton transfer — acids and bases

This mini-lesson covers Reactivity 3.1: Brønsted-Lowry acids and bases, conjugate pairs, strong vs weak, the pH scale and neutralisation.

Brønsted-Lowrythe pH scaleneutralisation Reactivity 3.1 — proton transfer reactions

Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you're ready.

Reactivity 3.1

Brønsted-Lowry acids and bases

A Brønsted-Lowry acid is a proton (H⁺) donor; a base is a proton acceptor.

When an acid donates a proton it becomes its conjugate base; a base becomes its conjugate acid. They differ by a single H⁺ — e.g. HCl / Cl⁻ and H₂O / OH⁻.

Quick check

Conjugate base

?What is the conjugate base of the acid HNO₃?
Reactivity 3.1

Strong versus weak

Strong acids/bases dissociate (ionise) essentially completely in water (e.g. HCl, NaOH). Weak acids/bases dissociate only partially (e.g. ethanoic acid, ammonia), setting up an equilibrium.

Strength (extent of dissociation) is not the same as concentration.

Quick check

Strong or weak?

?Which is a WEAK acid?
Reactivity 3.1

The pH scale

Water self-ionises: [H⁺][OH⁻] = Kw = 1 × 10⁻¹⁴ at 298 K. The pH scale measures acidity:

pH = −log[H⁺] and pH + pOH = 14lower pH = more acidic; each unit is a ×10 change in [H⁺]
Calculate

pH from [H⁺]

1A solution has [H⁺] = 1 × 10⁻³ mol dm⁻³. Calculate its pH.
pH = −log(1 × 10⁻³) = 3.
Calculate

pOH from pH

2A solution has pH = 11. Calculate its pOH.
pOH = 14 − pH = 14 − 11.
Calculate

Hydroxide from acid

3If [H⁺] = 1 × 10⁻² mol dm⁻³, then [OH⁻] = 1 × 10⁻ˣ. What is x?
[OH⁻] = Kw ÷ [H⁺] = 10⁻¹⁴ ÷ 10⁻² = 10⁻¹².
Reactivity 3.1

Neutralisation

Acids react with bases to form a salt and water: H⁺ + OH⁻ → H₂O. Acids also react with:

  • Carbonates → salt + water + CO₂
  • Reactive metals → salt + hydrogen
Quick check

Neutralisation product

?What are the products when hydrochloric acid neutralises sodium hydroxide?
Sort it

Acid, base or salt?

Tap a substance, then its category.

🍋 Acids

🧼 Bases

🧂 Salts

Match it

Match acid to conjugate base

Tap an item on the left, then its match on the right.

Acid
Conjugate base
Recap

The big ideas to know

Brønsted-Lowry: acid = proton donor, base = proton acceptor; conjugate pairs differ by H⁺

Strength: strong = fully dissociated, weak = partially (an equilibrium)

pH: pH = −log[H⁺]; pH + pOH = 14; Kw = [H⁺][OH⁻] = 10⁻¹⁴

Neutralisation: acid + base → salt + water

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