Acids and Bases
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What is the basis of the Bronsted-Lowry model of acids and bases?
Proton transfer
What is a Bronsted-Lowry acid?
Proton donator
What is a Bronsted-Lowry base?
Proton acceptor
What defines the strength of an acid?
Its ability to dissociate to release H+ ions in solution. This is given by Ka.
What is a conjugate acid/base pair?
Species that are differentiated by the gain/loss of an H+ ion
What is a weak acid?
Species that only partially dissociates to release H+ in aqueous solution
What is a strong acid?
Species that fully dissociates to release H+ in aqueous solution
Describe an acid/base reaction in aqueous solution using an equation.
HA + H2O -> H3O+ + A-
Why is the dislocation of a weak acid given using a reversible symbol?
The process is an equilibrium between the acid and its’ conjugate base, as both are only partially formed without reaching completion.
What is the difference between a mono basic and a dibasic acid?
One vs two replaceable hydrogen atoms in their structures
How do we calculate pH?
-log [H+]
How do we calculate [H+] from pH?
10^-pH
How do we apply dilution theory to pH?
If we introduce H2O, we increase the volume but number of H+ ions is constant So we just use multiply [H+] by the volume ratio (before:after) Then determine new pH
What does Ka represent?
The equilibrium constant for the dissociation of a weak acid in aqueous solution
How do we calculate Ka?
Ka = [H+][A-]/[HA]
What would a higher Ka represent in terms of acid strength?
Greater [H+] conc. at equilibrium Stronger acid as it dissociates to a greater extent
How do we calculate pKa?
-log (Ka)
What would a higher pKa mean about acid strength?
Less dissociation -> weaker acid
What assumptions can we make when calculating Ka for a weak acid in water?
[H+] = [A-] where H2O dissociation is negligible [H+] init. = [H+] eq. where negligible dissociation occurs for a weak acid
Why can we not use assumptions when calculating Ka for… strong weak acids weak strong acids
[HA] eq. /= [HA] init. [H+] /= [A-] But these assumptions would usually hold for most applications when completing calculations where assumptions are a foundational component
What is the value of the ionic product of water Kw?
10^-14
What does Kw represent?
The dissociation constant for water
Give an algebraic expression for Kw in pure water.
Ka = [H+][OH-]/[H2O] Kw = [H+][OH-] Kw ~ [H+]^2
What type of base can Kw be applied to during calculations?
Strong bases only