Acids, Bases and Buffers Flashcards
What is a base?
A species that can accept a proton
What is an acid?
A species that can donate a proton
What is an acid-base pair?
A pair of two species that transform into each other by gain or loss of a proton
What is the difference between a strong and weak acid?
- strong acids fully dissociate
- weak acids partially dissociate
What does Ka show?
The extent of acid dissociation
How do we find pKa?
-logKa
What is Ka?
[H+][A-]/[HA]
How do we find pH?
-log[H+]
How do we find [H+]?
10^-pH
What is the expression for Kw?
Kw= [H+][OH-]
What is a buffer solution?
A system that minimises pH changes in addition of small amounts of an acid or a base
What is a buffer solution?
A weak acid mixed with the salt of a weak acid e.g. CH3COOH/CH3COONa
Explain the role of the conjugate acid-base pair in an acid buffer solution
A weak acid dissociates partially, HA H+ + A-
A high concentration of conjugate base A- is formed.
-this pushes the equilibrium to the left so the concentration of H+ is very small
How does a buffer act when acid is added?
-conjugate base, A-, removes added acid When H+ ions ares added: •[H+] is increases •conjugate base, A-, reacts with H+ ions •equilibrium shifts to the left, removing most of added [H+]
How does a buffer act when alkali is added?
The weak acid, HA, removes added alkali
On addition of an alkali, OH-, to a buffer:
•[OH-] is increased
•the small concentration of H+ ions react with the OH- ions
• HA dissociates shifting the equilibrium to the right to restore most of H+ ions that reacted
Where is a buffer used in our body and how?
Carbonic acid-hydrogencarbonate buffer system in blood plasma:
•how the pH is controlled in the plasma
•carbonic acid acts as a weak acid, hydrogencarbonate acts as conjugate base
•increase in H+ in blood is removed by conjugate base: equilibrium shifts to left
•increase in OH- is removed by weak acid: small conc of H+ reacts with OH-, weak acid dissociates, shifting equilibrium to the right to restore H+
