`Bronstead-Lowry definition of acid
proton donors
Bronstead-Lowry definition of base
proton acceptors
Titration curve
plot of acid solution pH against vol of added titrant
Create a titration curve with following labelled:
A: Equivalence point
B: midpoint
C: xs OH- controls pH
What is significant about equivalence
mol(A-)equiv = mol(HA)init = mol(OH)to reach equiv.
what is significant about the midpoint of a weak acid (3)
molHA = molA-
[HA] = [A-]
pH = pKa
conjugate acid-base pair
HA+ and A-
%dissociation formula
%dissociation formula = [HA]diss / [HA]init
or
[H+]equil / [HA]init
how does concentration affect %dissociation
increasing dilution of solution increases %dissociation
increasing concentration of solution decreases %dissociation
initial molarity
concentration of HA if no dissociation occurs (before its mixed)
How to find [A-] at equivalence if you are titrating a weak acid
[A-] = (HAmol)init / [(volHA)i + (volOH-)added]
What is significant about strong acid’s midpoint
[A-] does not equal [HA] because when HA is mixed with water it immediately dissociates meaning that the solution you are titrating has 0 [HA]
When do indicators change colour
pH of solution is close to pKa of indicator
Acid - base indicator
weak organic acids that have a conjugate bases of a different colour
Standardized base solution
base that you know the concentration of
How to determine an unknown concentration of a known acid (3)
- titrate acid to equivalence using a standardized base solution
- Use acid - base indicator to recognize when you’ve reached equilibrium (solution changes colour)
- You know how much titrant you had to add to reach equilibrium
Why do indicators change colour
- Indicators are substances that undergo their own reaction with H⁺ ions in a solution, with a different coloured conjugate base
HIn= H^+ + In^- - The H+ in the solution forces the reaction to reach its midpoint
- At the midpoint of an indicator’s reaction, [HIn] and [In⁻] are equal.
- After, the midpoint, the indicator reaction shifts to favor the formation of the differently coloured conjugate base
Experiment P process (4)
- prepare a beaker of unknown M of acid, add indicator
- titrate NaOh with the unknown acid
- while titrating acid, regularly record pH using pH meter to get a titration curve
- record entire titration curve. Reaction will turn pink at equivalence
