Acids, Bases and Buffers Flashcards
What is the Bronsted-Lowry definition of an acid?
Proton donor
What is the Bronsted-Lowry definition of a base?
Proton acceptor
What does acid-base equilibria involve?
The transfer of protons
How do you find the pH of a strong acid?
pH = –log₁₀[H⁺]
How do you find the H⁺ concentration from pH?
10⁻ᵖᴴ
How dissociated is water?
Slightly dissociated
What is the expression for the ionic product of water?
Kw = [OH⁻][H⁺]
How do you calculate the pH of a strong base?
1) Kw = [OH⁻][H⁺]
2) Rearrange for [H⁺]
3) Substitute into pH = –log₁₀[H⁺]
Define strong acids/weak acid
Fully dissociated in solution
Define weak acid/weak base
Partially dissociated
What is the dissociation constant for a weak acid?
Ka
How is Ka related to Kc?
Kc [H₂O] = Ka
What is the Ka expression for the equation:
CH₃COOH + H₂O ⇌ CH₃COO⁻ + H₃O⁺
Ka = [CH₃COO⁻][H⁺] / [CH₃COOH]
How do you calculate the pH of a weak acid?
Ka = [H⁺]² / [CH₃COOH]
- solve for [H⁺]
- use equation pH = –log₁₀[H⁺]
How does temperature affect Ka?
When you increase temperature, you increase Ka
What is the ‘end point’?
When the indicator changes colour
What is the ‘equivalence point’?
When [H⁺] = [OH⁻]
What indicator should be used for a strong acid/ weak base titration?
methyl orange
What indicator should be used for a strong base/weak acid titration?
phenolphthalein
How would you measure the pH change for a weak acid/weak base titration and why?
A pH probe because there is no sharp increase in pH.
How to calculate the pH during a titration?
1) Calculate moles
2) Find whichever is in excess (x)
3) Find the concentration from the moles of x left
4) Find pH
What is monoprotic?
Donates only one proton
What is a buffer?
A buffer is able to resist changes to pH when moderate amounts of acid or base are added
What makes up an acidic buffer?
Weak acid + Salt from the weak acid and strong base