Topic 8.1: Acid and bases – Theories of acids and bases
Many reactions involve the transfer of a proton from an acid to a base.
• Understanding: A Brønsted–Lowry acid is a proton/H+ donor and a Brønsted–Lowry base is a proton/H+ acceptor.
▪ Brønsted-Lowry acid: define as a proton (hydrogen ion) donor
▪ Brønsted-Lowry base: defined as a proton (hydrogen ion) acceptor
▪ Hydronium ion (H3O+): ion formed when water molecules form a coordinate bond with a proton
• Protons in aqueous solution, H+ (aq), actually refers to presence of hydronium ions, H3O+ (aq).
• Understanding: Amphiprotic species can act as both Brønsted–Lowry acids and bases.
▪ Amphiprotic species: substance that can act as both Brønsted-Lowry acids or bases (can either donate or accept a proton)
• Common characteristic: all amphiprotic contain at least one hydrogen atom
• Examples of amphiprotic species: water, amino acids, proteins
▪ Amphoteric species: species that can act as both acid and base
• Amphiprotic species is a category of amphoteric species
• Understanding: A pair of species differing by a single proton is called a conjugate acid-base pair.
▪ Conjugate acid-base pair: pair of species differing by a single proton
• Brønsted-Lowry acid: has a conjugate base that has one less proton
• Brønsted-Lowry base: has a conjugate acid that has one more proton
• Applications and skills: Deduction of the Brønsted–Lowry acid and base in a chemical reaction.
▪ Characteristics of Brønsted-Lowry acid and base
• Conjugate acid-base pair: reactant and product differ by a proton
• Presence of hydrogen: B-L acids contain at least one hydrogen
• Applications and skills: Deduction of the conjugate acid or conjugate base in a
chemical reaction.
▪ Process of identifying conjugate acid or base
• Proton: conjugate acid or base differs by their respective conjugate by a proton
• Relative strength of acid/base: strong acids have weak conjugate bases, and vice versa
▪ Strong acid: acid that undergoes complete dissociation in water, and where the hydrogen has minimal affinity for the formed ions
▪ Weak acid: base that undergoes partial dissociation in water, establishing an equilibrium
• Nature of science: Falsification of theories—HCN altering the theory that oxygen was the element which gave a compound its
acidic properties allowed for other acid–base theories to develop.
• Nature of science: Theories being superseded—one early theory of acidity derived from the sensation of a sour taste, but this had
been proven false.
• Nature of science: Public understanding of science—outside of the arena of chemistry, decisions are sometimes referred to as "acid
test" or "litmus test".
• International-mindedness: Acidus means sour in Latin, while alkali is derived from the Arabic word for calcined ashes. Oxygene means
acid-forming in Greek, and reflects the mistaken belief that the element oxygen was responsible for a compound’s acidic properties.
• International-mindedness: Acid–base theory has been developed by scientists from around the world, and its vocabulary has been
influenced by their languages.
• Guidance: Lewis theory is not required here.
• Guidance: The location of the proton transferred should be clearly indicated. For example, CH3COOH/CH3COO– rather than
C2H4O2/C2H3O2–.
• Guidance: Students should know the representation of a proton in aqueous solution as both H+ (aq) and H 3O+ (aq).
• Guidance: The difference between the terms amphoteric and amphiprotic should be covered.
Many reactions involve the transfer of a proton from an acid to a base.
• Understanding: A Brønsted–Lowry acid is a proton/H+ donor and a Brønsted–Lowry base is a proton/H+ acceptor.
▪ Brønsted-Lowry acid: define as a proton (hydrogen ion) donor
▪ Brønsted-Lowry base: defined as a proton (hydrogen ion) acceptor
▪ Hydronium ion (H3O+): ion formed when water molecules form a coordinate bond with a proton
• Protons in aqueous solution, H+ (aq), actually refers to presence of hydronium ions, H3O+ (aq).
• Understanding: Amphiprotic species can act as both Brønsted–Lowry acids and bases.
▪ Amphiprotic species: substance that can act as both Brønsted-Lowry acids or bases (can either donate or accept a proton)
• Common characteristic: all amphiprotic contain at least one hydrogen atom
• Examples of amphiprotic species: water, amino acids, proteins
▪ Amphoteric species: species that can act as both acid and base
• Amphiprotic species is a category of amphoteric species
• Understanding: A pair of species differing by a single proton is called a conjugate acid-base pair.
▪ Conjugate acid-base pair: pair of species differing by a single proton
• Brønsted-Lowry acid: has a conjugate base that has one less proton
• Brønsted-Lowry base: has a conjugate acid that has one more proton
• Applications and skills: Deduction of the Brønsted–Lowry acid and base in a chemical reaction.
▪ Characteristics of Brønsted-Lowry acid and base
• Conjugate acid-base pair: reactant and product differ by a proton
• Presence of hydrogen: B-L acids contain at least one hydrogen
• Applications and skills: Deduction of the conjugate acid or conjugate base in a
chemical reaction.
▪ Process of identifying conjugate acid or base
• Proton: conjugate acid or base differs by their respective conjugate by a proton
• Relative strength of acid/base: strong acids have weak conjugate bases, and vice versa
▪ Strong acid: acid that undergoes complete dissociation in water, and where the hydrogen has minimal affinity for the formed ions
▪ Weak acid: base that undergoes partial dissociation in water, establishing an equilibrium
• Nature of science: Falsification of theories—HCN altering the theory that oxygen was the element which gave a compound its
acidic properties allowed for other acid–base theories to develop.
• Nature of science: Theories being superseded—one early theory of acidity derived from the sensation of a sour taste, but this had
been proven false.
• Nature of science: Public understanding of science—outside of the arena of chemistry, decisions are sometimes referred to as "acid
test" or "litmus test".
• International-mindedness: Acidus means sour in Latin, while alkali is derived from the Arabic word for calcined ashes. Oxygene means
acid-forming in Greek, and reflects the mistaken belief that the element oxygen was responsible for a compound’s acidic properties.
• International-mindedness: Acid–base theory has been developed by scientists from around the world, and its vocabulary has been
influenced by their languages.
• Guidance: Lewis theory is not required here.
• Guidance: The location of the proton transferred should be clearly indicated. For example, CH3COOH/CH3COO– rather than
C2H4O2/C2H3O2–.
• Guidance: Students should know the representation of a proton in aqueous solution as both H+ (aq) and H 3O+ (aq).
• Guidance: The difference between the terms amphoteric and amphiprotic should be covered.
