Acid & Base Theories
Overview
•
Acid & Base General Properties
(Arrhenius Theory)
•
Brønsted-Lowry Theory
•
Strong & Weak Acid & Base
General Properties of
Acid & Base
Simple Definition
• An acid is that it is a substance which neutralizes a base
• A base is that it is a substance which neutralizes an acid
• OR…
Simple Definition
• An acid is a substance that releases hydrogen ions when it
dissolves in water.
• A base is a substance that releases hydroxide ions when it
dissolves in water.
• This is the Arrhenius Definition
Simple Definition
Simple Definition
Simple Definition
Simple Definition
General Properties of Acid
Acid + Metal →
Salt + H2 (hydrogen gas)
General Properties of Acid
Acid + Metal oxide →
= Basic oxide
Salt + Water
General Properties of Acid
Acid + Base →
Salt + Water
General Properties of Acid
Acid + Carbonate salt →
Salt + Water + CO2
General Properties of Acid
Acid + Salt →
Acid + Salt
General Properties of Base
Base + Non-metal oxide →
= Acidic oxide
Salt + Water
General Properties of Base
Base + Acid →
Salt + Water
General Properties of Base
Base + Salt →
Base + Salt
Brønsted–Lowry Theory of
Acid & Base
Brønsted–Lowry Definition
• The previous definition is limited
• Especially for reaction with water
Brønsted–Lowry Definition
• New definition is based on the idea that in an acid–base reaction, a proton is
transferred from an acid to a base (a proton is a hydrogen ion, H+).
Brønsted–Lowry Definition
• A Brønsted–Lowry acid is a proton donor.
• A Brønsted–Lowry base is a proton acceptor.
• Remember: proton = H+
Brønsted–Lowry Definition
• Now, we can explain some reactions with water.
• They are also acid-base reactions.
• Who donated a proton?
•
Who accepted a proton?
Brønsted–Lowry Definition
Brønsted–Lowry Definition
Brønsted–Lowry Definition
In this case, water acts as an acid
Brønsted–Lowry Definition
Brønsted–Lowry Definition
• Water can act as both acid and base
• Water is amphoteric
Brønsted–Lowry Definition
Brønsted–Lowry Definition
Brønsted–Lowry Definition
• An acid reacts with another acid
• But one acts as a base
Brønsted–Lowry Definition
These substances can act as both acid and base.
• What will it become after gaining a proton?
• What will it become after losing a proton?
H2O
NH3
HSO4-
H2PO4-
Brønsted–Lowry Definition
Conjugate Acid & Base
• So far, we only looked at acid & base as reactants
• In equilibrium, we also need to look at products
Conjugate Acid & Base
• In forward reaction
• Which one is acid? Which one is base?
Conjugate Acid & Base
• In reverse reaction
• Which one is acid? Which one is base?
Conjugate Acid & Base
acid
base
Conjugate Acid & Base
• Identify acid and base on both sides
Conjugate Acid & Base
If a reactant is linked to a product
by the transfer of a proton we call
this pair a conjugate pair.
Conjugate Acid & Base
Forward reaction:
• Cl- is the conjugate base of the acid HCl
• H3O+ is the conjugate acid of the base H2O.
Conjugate Acid & Base
Reverse reaction:
conjugate acid
• HCl is the _________________
of the base
Clconjugate base
• H2O is the ________________
of the acid
H3O+
Conjugate Acid & Base
Conjugate Acid & Base
Conjugate Acid & Base
In each equilibrium, identify the CAs and CBs
Strong & Weak
Acid & Base
Strong Acid & Base
• Almost completely dissociated (ionized)
• Position of equilibrium is far over right
• Almost irreversible reaction
Strong Acid & Base
• Acids that dissociate almost completely in solution are called
strong acids.
• Bases that dissociate almost completely in solution are called
strong bases.
Strong Acid & Base
• The mineral acids, hydrochloric acid, sulfuric acid and nitric
acid, are all strong acids.
• The Group 1 metal hydroxides are strong bases.
Weak Acid & Base
• Partially dissociated (ionized)
• Position of equilibrium is over left
• Reversible reaction
Weak Acid & Base
• Acids that only partially dissociate in solution are called
weak acids.
• Bases that only partially dissociate in solution are called
weak bases.
Weak Acid & Base
• Weak acids include most organic acids, hydrocyanic acid
(HCN), hydrogen sulfide and carbonic acid.
• Ammonia, amines and some hydroxides of transition metals
are weak bases.
PH Scale
•
Acidic solutions have pH values
less than 7
•
Basic solutions have pH values
greater than 7
PH Scale
Past Papers