Acids, Bases and Buffers

Question 0

What is a base?

Answer 0

A species that can accept a proton

Question 1

What is an acid?

Answer 1

A species that can donate a proton

Question 2

What is an acid-base pair?

Answer 2

A pair of two species that transform into each other by gain or loss of a proton

Question 3

What is the difference between a strong and weak acid?

Answer 3

• strong acids fully dissociate

- weak acids partially dissociate

Question 4

What does Ka show?

Answer 4

The extent of acid dissociation

Question 5

How do we find pKa?

Answer 5

-logKa

Question 6

What is Ka?

Answer 6

[H+][A-]/[HA]

Question 7

How do we find pH?

Answer 7

-log[H+]

Question 8

How do we find [H+]?

Answer 8

10^-pH

Question 9

What is the expression for Kw?

Answer 9

Kw= [H+][OH-]

Question 10

What is a buffer solution?

Answer 10

A system that minimises pH changes in addition of small amounts of an acid or a base

Question 11

What is a buffer solution?

Answer 11

A weak acid mixed with the salt of a weak acid e.g. CH3COOH/CH3COONa

Question 12

Explain the role of the conjugate acid-base pair in an acid buffer solution

Answer 12

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

Question 13

How does a buffer act when acid is added?

Answer 13

-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+]

Question 14

How does a buffer act when alkali is added?

Answer 14

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

Question 15

Where is a buffer used in our body and how?

Answer 15

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+