Acids and Bases Flashcards
Define bronsted-Lowry acid
Give an example
Proton donor
HA + H2O → H3O+ + A-
Define bronsted-Lowry base
Give an example
Proton acceptor
B + H2O → BH+ + OH-
Define strong acid
Completely dissociates
Define weak acid
Slighty dissociates
Define strong base
Completely ionises
Define weak base
Slightly ionises
What happens during acid base equilibria?
Protons are transferred from acid to base
Does water fully dissociate or slightly?
Slightly dissociates
Where is kw derived from?
Kc x [H2O]
Ionic product of water
Unit
Kw = [H+] [OH-]
mol2 dm-6
Does the value of Kw change as the temp changes?
Yes, it varies w/ temp
What is the value of Kw at 298k?
1.00 x 10-14 mol2 dm-6
Why is a solution w/ pH 6 still considered neutral?
[H+] = [OH-]
Equation for pH
pH = -log [H+]
pH to conc equation
[H+] = 10-pH
Give the expression of Ka
Unit
Ka = [H+] [A-] / [HA]
Ka = [H+]2 / [HA]
mol dm-3
When is Ka used?
Weak acid
How do you work out Ka from pKa?
Ka = 10-pKa
How do you work out pKa from Ka?
pKa = -log (Ka)
Would you expect strong acids to have higher or lower pKa value than weak acids?
Lower
What is the vertical line in a pH curve?
Equivalence point - neutral
How do you work out which indicator to use?
The one that changes colour over narrow pH range that lies on vertical part of pH curve
Methyl orange
Colour change
pH range
- Red to yellow
- 3.1 - 4.4
Phenolphthalein
Colour change
pH range
- Colourless to pink
- 8.3 - 10