Bronsted-Lowry acid
Proton donor
Bronsted-Lowry base
Proton acceptor
Conjugate acid-base pair
A pair of species differing by a single proton.
Amphiprotic species
Species that can act as both Bronsted-Lowry acids and bases.
Examples of amphiprotic species:
Water
Hydrogen carbonate ion (HCO3- can become CO3 2- or H2CO3)
Hydrogen sulfate ion (HSO4-)
Dihydrogen phosphate (HPO4-)
Hydrogen phosphate (HPO4 2-)
The ion product constant of water (Kw)
The product of [H+] and [OH-] in water at a particular temperture.
The Kc (equilibrium constant) of water.
A constant at a certain temperature, as Kw is an equilibrium constant and is temperature dependent.
(Constant => when [H+] increases, then [OH-] decreases, and so on.)
Shows an inverse relationship between [H+] and [OH-].
Do acid-base equilibria lie in the direction of the weaker or stronger conjugate?
The weaker conjugate.
Lewis acid
An electron-pair acceptor
Electrophiles are Lewis acids.
Lewis base
An electron-pair donor
Nucleophiles are Lewis bases.
What type of bond is formed when a Lewis base reacts with a Lewis acid?
Coordination bond
What values describe the strengths of weak acids and bases?
Ka, Kb, pKa, pKb.
Temperature dependent.
Ka x Kb =
Kw
Salts of weak acids and strong bases
The salt fully dissociates to form ions.
The ion of the strong base (i.e. metal cation) does not have acid-base activity.
The ion of the weak acid is the conjugate base tht reacts with water to form ethanoic acid, a weak acid. The weak acid does not fully ionise in water, and OH- ions are formed from this reaction that make the solution alkaline (pH>7) at 298K.
Salt hydrolysis of parent acid and base that have approximately the same value of Ka / Kb
Neither (or both?) ions will hydrolyse and the salt produced will have a pH of around 7.
Acid-base indicator
A weak acid or weak base in which the dissociated and undissociated forms have different coloours.
Exists in an equilibrium between the two forms,
How can the position of equilibrium of an acid-base indicator be changed?
By adding an acid or a base.
End-point
The point at which an indicator changes colour during an acid-base titration.
The pH of the end-point approximately corresponds to its pKa value.
Buffer solution
A solution that resists changes in pH on the addition of small amounts of acid or alkali.
Works by minimising stress by shifting the position of equilibrium of the system to counteract the change (Le Chatelier’s principle).
Composition of buffers
A weak acid or base as the primary component.
In order to make a buffer solution that can respond to stress, the system at equilibrium must contain a relatively equal amount of both the weak acid/base and the conjugate base/acid.
Otherwise, the response to the stress would not be very effective.
The conjugate base must be added to the weak acid to provide a sufficient concentration. The conjugate base can be added to the solution by adding a salt that contaiins the conjgate base as the anion, and its cation must not provide any acid-base activity to the buffer solution (strong acid).
Ratio of a buffer solution with the largest capacity
1:1
Most resistant to change.
Equivalence point
