Buffers Flashcards
What is the definition of a buffer?
A solution that maintains an approximately pH on addition of small amounts of acid or alkali
What is an acidic buffer made up of?
A mixture of a weak acid [HA] + Salt [A-]
What are the 2 ways of forming an acidic buffer?
1) Weak acid + its salt i.e. [HA] + [A-]
2) Partly neutralise a weak acid to form [HA] and some [A-]
What happens when H+ are added to an acidic buffer solution?
The salt will react with the added [H+] ions to create more of the weak acid i.e. the equilibrium shifts to the left
What happens when H+ are added to an alkali buffer solution?
Added [OH-] ions will react with [H+] ions to create water. the equilibrium will shift to the right.
What is an basic buffer made up of?
A mixture of a weak base [B] and its salt [BH+]
What are the 2 ways of forming an basic buffer?
1) Weak base + its salt i.e. [B] + [BH+]
2) Partly neutralise a weak base to form [B] and some [BH+]
What does the pH of an acidic buffer solution depend on?
1) The Ka of the acid
2) The ratio of weak acid to salt
How do you calculate the pH of an acidic buffer solution?
[H+]= Ka[Ha]/[A-]
When is pH equal to pKa?
When [HA] and [A-] are equal.
As a rule of thumb what is the buffer range?
pKa +/- 1
