pH and Buffers Pre-AP Biology 1

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?

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

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

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) 5

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

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?

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

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

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

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

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

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

Link to Bellwork How is a Buffer like a sponge?

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

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