# Self Ionization of Water and the pH Scale

13 Slides90.96 KB Self Ionization of Water and the pH Scale Ionization of Water Water will naturally break down into equal ions in water: 2H2O H3O (aq) OH- (aq) This is called the ionization of water. pH Scale scale used by chemists to measure the acidity of a substance; a measure of the amount of H in the solution. scale goes from 0 – 14 NEUTRAL 7 0 ACIDIC OH- H3O (We are counting how many hydronium ions are in a solution!) OH- H3O 14 BASIC OH- H3O (We are counting how many hydroxide ions are in a solution!) pH Scale pH describes a balance between hydroxide ions (OH-) and hydronium ions (H3O ) Note: [H ] and [H3O ] are equivalent! We will use them interchangeably. pH stands for “parts hydrogen ion” pOH stands for “parts hydroxide ion” Is It An Acid or a Base? 1. pH 4 2. pH 10 3. pH 7 The pH scale is not linear! The lower the pH, the higher the concentration of hydronium ions. The pH scale changes 10 times between each step. Example Problem: How many times more acidic is solution A than solution B? A B pH 4 pH 6 pH 3 pH 5 The number of zeros the difference in pH. pH 8 pH 11 Ex. 6-4 2 so, 100 times. pH 7 pH 4 Estimating pH from [H3O ] The pH of a solution can be estimated by looking at the concentration of hydronium (H3O ). The exponent is the estimated pH of the substance! Example: [H3O ] 1.0 x 10-3 M pH 3 Estimating pH from [H3O ] The pH of a solution can be estimated by looking at the concentration of hydronium (H3O ). Example: [H3O ] 1.0 x 10-12 M pH 12 Estimating pH from [H3O ] The pH of a solution can be estimated by looking at the concentration of hydronium (H3O ). Example: [H3O ] 3.1 x 10-12 M Estimating pH from [H3O ] The pH of a solution can be estimated by looking at the concentration of hydronium (H3O ). Example: [H3O ] 3.1 x 10-12 M pH a little less than 12 Estimating [H3O ] from pH Example: pH 9.0 So, [H3O ] 1.0 x 10-9 M Estimating [H3O ] from pH You try: pH 7.0 pH 2.0 pH 8.0