pH , Acids and BasesPg 164-165

pHReminder: Water is held together by

___________________ bonds.These are relatively __________ bonds.These bonds are constantly _________ and

_____________.Water molecules can naturally break apart.

This is called the dissociation of water.

Acids, Bases and pHOne water molecule in 550 million

naturally dissociates into a Hydrogen Ion (H+) and a Hydroxide Ion (OH-)

Hydrogen Ion Hydroxide Ion Acid Base

H2O H+ + OH-

The pH Scale

**Some compounds form acids or bases

Scientists use something called the pH scale to measure how acidic or basic a liquid is

The scale looks at the concentration of positively charged hydrogen ions (H+) in a solution vs. the amount of negatively charged hydroxide ions (OH-)

The scale goes from values 0 through 14.

Brain pop

Acids

Tastes sour Corrodes metals

• An acid releases hydrogen ions when it dissolves in water.

- High H+ concentration- Low OH- concentration- pH less than 7

Bases

Tastes bitter, chalkyFeels soapy, slippery

A base releases hydroxide ions

A B

Left to right

Summary! If you have an ionic compound and you put it

in water, it will break apart into two ions.If one of those ions is H+, the solution is acidic. If one of the ions is OH-, the solution is basic.

There are other ions that make acidic and basic solutions, but we won't be talking about them

here.

ACID BASE

NeutralPure water contains small, but equal

amounts of ions: H+ and OH-On the pH scale the number is 7

Acids vs BasesAcids: Anything that dissolves in water and

adds H+. Bases: Anything that dissolves in water and

adds OH- ions.

BuffersBuffer - mixtures that can react with acids or

bases to prevent major pH changes.

Buffered aspirin has a coating on it to prevent the acids in your stomach from dissolving it right away.

1001

2

3

4

5

6

7

8

9

3Amount of base added

Bufferingrange

4 52

pH

Buffers & Cellular RegulationpH of cells must be kept ~7

pH affects the shape of moleculesshape of molecules affects functionpH affects cellular function

Buffers Control pH donate H+ when

[H+] falls absorb H+ when

[H+] rises

Honors Biology