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PH and Buffers Pre-AP Biology 1.

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Presentation on theme: "PH and Buffers Pre-AP Biology 1."— Presentation transcript:

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


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