L1 - Theories of Acids & Bases

objectives

Understandings:

• A Brønsted–Lowry acid is a proton/H+ donor and a Brønsted–Lowry base is a proton/H+ acceptor.

• Amphiprotic species can act as both Brønsted–Lowry acids and bases.

• A pair of species differing by a single proton is called a conjugate acid-base pair.

Applications and skills:

• Deduction of the Brønsted–Lowry acid and base in a chemical reaction.

• Deduction of the conjugate acid or conjugate base in a chemical reaction.

Guidance:

• Lewis theory is not required here.

• The location of the proton transferred should be clearly indicated. For example, CH3COOH/CH3COO– rather than C2H4O2/C2H3O2–.

• Students should know the representation of a proton in aqueous solution as both H+ (aq) and H3O+ (aq).

• The difference between the terms amphoteric and amphiprotic should be covered.

Brønsted-Lowry Acids and Bases

ACID = proton donor

HCl ——> H⁺(aq) + Cl¯(aq)

BASE = proton acceptor

NH₃ (aq) + H⁺(aq) ——> NH₄⁺(aq)

Conjugate Systems

Acids are related to bases

ACID ⇌ PROTON + CONJUGATE BASE

Bases are related to acids

BASE + PROTON ⇌ CONJUGATE ACID

For an acid to behave as an acid, it must have a base present to accept a proton...

example CH₃COO¯ + H₂O ⇌ CH₃COOH + OH¯

Base 1 acid 1 acid 2 base 2

HA + B ⇌ BH⁺ + A¯

Strong Acids and Bases

STRONG ACIDS - completely dissociate (split up) into ions in aqueous solution

e.g. HCl ——> H⁺(aq) + Cl¯(aq) MONOPROTIC 1 replaceable H

HNO₃ ——> H⁺(aq) + NO₃¯(aq)

H₂SO₄ ——> 2H⁺(aq) + SO₄^2-(aq) DIPROTIC 2 replaceable H’s

STRONG BASES - completely dissociate into ions in aqueous solution

e.g. NaOH ——> Na⁺(aq) + OH¯(aq)

Amphiprotic Species

Amphiprotic Species can behave as both Bronsted-Lowry Acids and Bases meaning they can both accept and donate protons