3.1.1—Brønsted-Lowry theory

A Brønsted–Lowry acid donates H+ and a Brønsted–Lowry base accepts H+. An alkali is a base that is soluble in water.

Follow the proton: the species losing it is the acid and the species gaining it is the base.

Pair species that differ by exactly one H⁺ to identify conjugate acid–base pairs. Charge alone does not decide the role: in NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺, NH₄⁺ is the proton donor and water is the acceptor.

Representative question

[Maximum number: 2]

Describe whether ammonia acts as a Brønsted-Lowry acid or base in its reaction with water. Include an equation in your answer.

base AND accepts $\mathrm{H}^{+}$ /hydrogen ion/proton $\boldsymbol{}$ $\begin{aligned} \mathrm{NH}_{3}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{I}) \rightleftharpoons \mathrm{NH}_{4} \mathrm{OH}(\mathrm{aq}) \boldsymbol{O} \boldsymbol{R} \end{aligned}$ $\mathrm{NH}_{3}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightleftharpoons \mathrm{NH}_{4}^{+}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq}) \downarrow$

Accept either type of arrow

Retrieve the route: track proton transfer and conjugates, calculate pH and Kw, distinguish strength, balance neutralization, read titration curves, use Ka/Kb and hydrolysis, select indicators, and explain and calculate buffer behaviour.

Check donor versus acceptor, one-proton differences, logarithm direction, ion comparison, strength versus concentration, equivalence versus endpoint, pKa landmarks, conjugate equations and dilution ratios.

3.1.1—Brønsted-Lowry theory

Brønsted–Lowry Acids and Bases

Assigning Acid and Base Roles

Assessment in practice

Proton Transfer Reactions Summary

Question 1