First question in any acid/base problem
Is a strong acid or strong base present?
Yes → BCA reaction first
No → ICE or Henderson
When do I do a BCA table?
Whenever H⁺ or OH⁻ reacts with something weak
Weak acid + strong base
Weak base + strong acid
A⁻ + strong acid
HA + strong base
Weak acid + strong base reaction
HA + OH → A− + H20
Weak base + strong acid reaction
BH+ → B + H+
After BCA, if only HA remains →
Ka, ICE
After BCA, if only A⁻ remains →
Kb, ICE
After BCA, if only B remains →
Kb, ICE
After BCA, if only BH⁺ remains →
Ka, ICE
After BCA, if HA + A⁻ remain →
Buffer → Henderson
pH = pKa + log(H- / HA)
After BCA, if B + BH⁺ remain →
Buffer → Henderson
pOH = pKb + log(BH+ / B)
- then subtract from 14 to get pH
Halfway point in titration
Weak acid titration → pH = pKa
Weak base titration → pOH = pKb
How do I know before / at / after equivalence?
Acid < Base: before eq → buffer
Acid = Base: equivalence
Acid > Base: After eq
Condition | Region |
What is HA
Weak Acid
What is A-
Conjugate Base of HA
What is B
Weak Base
What is BH+
Conjugate Acid of Base
What is H+
Strong Acid Proton
What is OH-
Strong Base
How to calculate halfway point?
moles of added strong acid/base is equal to 1/2 moles of original weak base or acid — ph = pka
How to calculate equivalence point?
when moles of strong acid or base are equal to moles of weak acid or base
Q < Ksp
Unsaturated
Q = Ksp
Equilibrium
Q>Qsp
Supersaturated
