Topic 12 Acid Based Equilibria Flashcards
What are Bronsted-Lowry acids and bases?
Bronsted-Lowry acid - A proton donor
Bronsted-Lowry base - A proton acceptor
What is a Bronsted-Lowry reaction?
A reaction that involves the transfer of a proton (H⁺ ion) between an acid and base.
What are conjugate acids and bases?
Conjugate Acid - The product formed when a base accepts a proton
Conjugate Base - The product formed when an acid donates a proton
What do the terms amphoteric and amphiprotic mean?
Amphoteric - A substance that can act as both and acid and a base
Amphiprotic - A substance that can both donate and accept protons (H⁺ ions)
What is the difference between amphoteric and amphiprotic substances?
All amphiprotic substances are amphoteric as they act as an acid when donating protons and as a base when accepting protons. However, not all amphoteric substances are amphiprotic because they do not contain H⁺ ions to donate.
For example Aluminium Oxide. They acts as bases as they accept H⁺ ions to form water. However they do not contain any H⁺ ions to donate but do however act as an acid by reacting with bases such as NaOH.
How can you calculate the pH of a substance?
pH = - log₁₀[H⁺ (aq)]
or
pH = 14 - pOH
[] means concentration
How can you calculate the pOH of a substance?
pOH = - log₁₀[OH⁻ (aq)]
[] means concentration
or
pOH = 14 - pH
What does the term acid dissociation mean?
The process of acids forming ions in a solution. This is usually when acids are added to water as they dissolve. The extent of dissociation that occurs helps distinguish between strong and weak acids.
What is a strong acid?
An acid that is fully ionised (or dissociated) when dissolved in water.
What is a weak acid?
An acid that is partially ionised (or dissociated) when dissolved in water.
What is Kᵥᵥ?
The equilibrium constant for the ionisation of water. This is defined by the expression:
Kᵥᵥ = [H⁺ (aq)][OH⁻ (aq)] = 1.0 x 10⁻¹⁴
or
logKᵥᵥ = log[H⁺ (aq)] + log[OH⁻ (aq)] = -14
∴
-logKᵥᵥ = -log[H⁺ (aq)] - log[OH⁻ (aq)] = 14
What is the pKᵥᵥ?
This is defined by the expression pKᵥᵥ = -log[H⁺ (aq)] - log[OH⁻ (aq)] = -logKᵥᵥ ∴ pKᵥᵥ = pH - pOH = 14 ∴ pH = 14 - pOH
What is the acid dissociation constant?
This is the name given to the equilibrium constant K꜀ for the ionisation of a weak acid.
It is given the expression:
Kₐ = [H⁺ (aq)][A⁻ (aq)] / [HA (aq)]
In weak acids:
Ka = [H⁺ (aq)]² / [HA (aq)]
What is the equivalence point?
This is the point in a titration which is reached when the amount of reactant added from a burette is just enough to react exactly with all the measured amount of chemical in the flask according to the balanced equation.
What is the end point?
The point in a titration at which a colour change or pH change indicated that just enough of the solution in the burette has been added to react with the chemical in the flask.
