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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