14. Acids, bases and buffers Flashcards
What are the possible classifications of acids and bases?
- Arrhenius: A - increases H+ ions, B - increases OH- ions
- Bronsted - Lowry: A - H+ donor, B - H+ acceptor
- Lewis: A - e pair acceptor, B - e pair donor
What is an amphoteric compound?
Can act both as an acid and a base: H2O
Explain conjugate acid - base pairs? Consider their strength
How to determine pH of strong acids / bases?
[H+]=[acid]
[`OH-]=[base]
How to determine pH of weak acids / bases?
Equilibrium constant must be considered using ICE method
What is the relation between Ka and Kb?
Ka x Kb = Kw
pKa + pKb = 14
How to compare acidity between two acids given the structure and pKa?
Inductive effect: stronger inductive effect (higher charge density) -> anion less stable - more basic
Inductive effect: weaker inductive effect (lower charge density) -> anion more stable - more acidic
Compare acidity of methanoic, ethanoic and propanoic acids
The longer the C chain - the stronger the inductive effect - the weaker the acid
How does resonance influence the strength of an acid?
The more resonance strcutures the acid has → the more stable it is → the stronger it is → the lower the pKa
Inductive effect also influences the strength of the acid - but resonance more
How is the pH of salts predicted?
Analysing from which acids and bases the salt was made
What is a buffer?
Buffer - a solution which resist the pH change when a small amount of acid / base is added - equilibrium shifts to minimise the effect
Buffer = mixture of weak acid and its conjugate anion
What happens to the equilibrium in buffer when small amount of acid is added?
What happens to the equilibrium in buffer when small amount of base is added?
What happens to the equilibrium in buffer when large amount of acid / base is added?
What is the Henderson-Hasselbalch equation?
