III. pHA. Dissociation of Water Molecules:

1. Water molecules split to form ions.

H2O H+ OH- + (hydroxide ion)

*The dissociation of water is reversible.

H+ + OH- H2O

3. Certain substances can cause imbalances in these concentrations.

2. In pure water, H+ and OH- are equal in concentration.

a. These substances are

called ACIDS and BASES.

B. Acids 1. Add (donate) more H+ when dissolved in

water.

2. More H+ = stronger acid

3. Taste sour

• Example: HCl H+ and Cl-

C. Bases1. Add more OH- when dissolved in water.

2. More OH- = stronger base

3. Alkaline

4. Taste bitter

• Example: NaOH Na+ and OH-

D. pH scaleThe measure of how acidic or

basic a compound is

7 1 2 3 4 5 6 8 9 10 11 12 13 14

Neutral

Acidic Basic

strong weak strongweak

[H+] > [OH-] [H+] < [OH-]