1. The substances on the left side of the number line (from 0 to 7) are all acids. The substances on the right side of the number line (from 7 to 14) are called bases. The substances located in the middle of the number line (around 7) are called neutral substances.

2. Acids are substances that add H+ to solution. Bases are substances that add OH- to solution. Neutral substances do not add H+ or OH- to solution. Arrhenius Definition of Acids and Bases: An acid is any substance that adds hydrogen ion (H+) to solution. A base is any substance that adds hydroxide ion (OH-) to solution.

3. Brønsted-Lowry Definition of Acids and Bases: An acid is a proton donor. A base is a proton acceptor. Acids and bases that break apart (dissociate) completely in solution are called strong acids and strong bases. Acids and bases that do not dissociate completely in solution are called weak acids and weak bases.

4. The pH scale is a logarithmic scale that describes the concentration of H + ions in solution. pH is related to [H + ] by the formula pH = -log [H + ]

5. H + concentrationOH – concentrationpH 1.0 X 10 0 M1.0 X 10 –14 M0 1.0 X 10 –1 M1.0 X 10 –13 M1 1.0 X 10 –2 M1.0 X 10 –12 M2 1.0 X 10 –3 M1.0 X 10 –11 M3 1.0 X 10 –4 M1.0 X 10 –10 M4 1.0 X 10 –5 M1.0 X 10 –9 M5 1.0 X 10 –6 M1.0 X 10 –8 M6 1.0 X 10 –7 M 7 1.0 X 10 –8 M1.0 X 10 –6 M8 1.0 X 10 –9 M1.0 X 10 –5 M9 1.0 X 10 –14 M1.0 X 10 –0 M14 More acidic More basic neutral

6. In any solution, the product of the hydrogen ion, H +, concentration and hydroxide ion, OH –, concentration is a constant. Water dissociates into H + and OH – ions.

7. Adding water to an acid or a base dilutes the solution, making it less acidic or less basic. An acid can never be turned into a base by diluting it with water, and a base can never be turned into an acid by diluting it with water.

8. Each time the H+ concentration is diluted tenfold, the pH number goes up 1 unit. pH H+ concentration (decimal number) H+ concentration (scientific notation) 20.010 mol/L1.0 X 10 –2 mol/L 30.0010 mol/L1.0 X 10 –3 mol/L 40.00010 mol/L1.0 X 10 –4 mol/L 50.000010 mol/L1.0 X 10 –5 mol/L 60.0000010 mol/L1.0 X 10 –6 mol/L 70.00000010 mol/L1.0 X 10 –7 mol/L