1. pH and Buffers
Pre-AP Biology 1

2. Bellwork
You have a large puddle of water on the floor, explain how the sponge works to remove the water. How do you remove the water collected by the sponge?

3. Objectives Define pH Explain why the pH scale is logarithmic
Distinguish between acids and bases
Explain how a buffer works

4. Dissociation of Water Water molecules break down
into hydrogen ions (H+) and hydroxide ions (OH-)
H2O  H+ + OH –
[ H+][OH-] =10-14 4

5. pH Scale pH = -log [H+] Use logarithms to make scale more compact
Called a “Log Scale”
Like Richter Scale
Each pH Unit represents
a power of 10
= 7 (neutral) 5

7. pH Scale Problem
Cola has a pH of 3 and blood plasma has a pH of 7. How much greater is the hydrogen ion concentration of cola than blood plasma? 7

8. pH Scale Problem
Milk of magnesia has a pH of 10. Vinegar has a pH of 3. How much greater is the hydrogen ion concentration of vinegar relative to Milk of Magnesia?

9. Acids Increase H+ concentration in solution
H+ > OH- is an acidic solution
pH < 7; [H+] > [OH-]
Example: HCl
HCl  H+ + Cl- 9

10. Bases Created in one of two ways Reduce H+ concentration
Ex. NH3 + H+  NH4+
Increase OH- concentration
Ex. NaOH  Na+ + OH-
pH > 7; [OH-] > [H+] 10

11. pH problems If [OH-] is 1 x 10-11 M a.What is the [H+] concentration?
b.What is the pH? 11

12. Practice Problem
If the pH is 1, what is the [H+] and [OH-]? 12

13. Biological Significance
Strong acids aid in digestion
Blood = 7.4, which helps carry oxygen throughout your body 13

14. Role of Buffers Chemicals that moderate pH
by accepting H+ when too acidic
by donating H+ when too basic 14

15. Link to Bellwork
How is a Buffer like a sponge?

16. Buffer Question If I add an acid to water what will happen to the pH?
If I add an acid to a buffer what will happen to pH? 16

17. Write a “snapshot” of today’s learning in 25 words or less.
teacher provides a prompt from the lesson
students must write a “snapshot” of the lesson in 25 words or less
teacher uses a strategy to check all 17 17