ph and buffers pre-ap biology. bellwork you have a large puddle of water on the floor, explain how...
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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 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
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)
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?
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-
Bases
Created in one of two waysReduce H+ concentration
Ex. NH3 + H+ NH4+
Increase OH- concentration Ex. NaOH Na+ + OH-
pH > 7; [OH-] > [H+]
pH problems
If [OH-] is 1 x 10-11 M
a.What is the [H+] concentration?
b.What is the pH?
Practice Problem
If the pH is 1, what is the [H+] and [OH-]?
Biological Significance
Strong acids aid in digestion Blood = 7.4, which helps carry oxygen
throughout your body
Role of Buffers
Chemicals that moderate pH by accepting H+ when too acidicby donating H+ when too basic
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?
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