1. pH Scale & Buffers
Chapter 2
Biochemistry

2. You must know! How to interpret the pH scale.
How to calculate pH when given H+ or OH- concentrations
How changes in pH can alter biological systems.
The importance of buffers in biological systems.

3. pH Scale
In an aqueous solution some water and other molecules will ionize
Ex: H2O  H+ (hydrogen ion) and OH- (hydroxide ion)
1/10,000,000
The potential of Hydrogen (pH) is a measurement of the ratio of H+ relative to water molecules
1/10,000,000 = 10-7; pH = 7
pH indicates the acidity and alkalinity of aqueous (water based) solutions.

5. pH Scale It is a negative, logarithmic scale: pH = -log [H+]
Example: A solution has a ratio of 10-7 H+ per H2O therefore the solution has the pH of?
What if the solution has a ratio of 10-7 [OH-] per H2O?

6. Acids vs Bases
Acid
Solution that has a higher concentration than water of H+ ions (low concentration of OH-)
Has a pH < 7
Base
Solution that has a lower concentration than water of H+ (high concentration of OH-)
Has a pH > 7

7. More Practice
What is the ratio of H+ to water in a solution with a pH of 10?
What is the pH of a solution with a ratio of hydroxide ions to water molecules of 10-8?
How many times more acidic is a solution with a pH of 3 than a solution with a pH of 6?
What is the pH of a solution with a ratio of 10-2 OH- ions to H2O?

8. pH Homeostasis
Chemical reactions in living things (respiration, photosynthesis) depend on a stable pH
Your blood has a pH of 7.4
It is deadly if it raises to 7.5 or drops to 7.3
Buffers like carbonic acid H2CO3 (blood plasma and oceans) minimize pH change when an acid or base is added.
Most biological solutions have a natural ability to buffer: blood, milk, saliva, egg white
Buffers add H+ ions when they are running low or remove H+ ions when there are too many