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PH and Buffers Pre-AP Biology. Bellwork You have a large puddle of water on the floor, explain how the sponge works to remove the water. How do you remove.

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Presentation on theme: "PH and Buffers Pre-AP Biology. Bellwork You have a large puddle of water on the floor, explain how the sponge works to remove the water. How do you remove."— Presentation transcript:

1 pH and Buffers Pre-AP Biology

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-) H 2 O  H + + OH – [ H + ][OH - ] =10 -14

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 [H + ]=[OH - ] @pH = 7 (neutral)

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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?

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 [OH-] Example: HCl  HCl  H + + Cl -

10 Bases Created in one of two ways  Reduce H+ concentration Ex. NH 3 + H +  NH 4 +  Increase OH - concentration Ex. NaOH  Na + + OH - pH > 7; [OH - ] > [H+]

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

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

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

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

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?

17 17Snapshot Write a “snapshot” of today’s learning in 25 words or less.

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