Indicators and Hydrogen Ions and Acidity Section 19.2

To test a diagnosis of diabetic coma, a doctor orders several tests, including the acidity of the patient’s blood. Results from this test will be expressed in units of pH. You will learn how the pH scale is used to indicate the acidity of a solution and why the pH scale is used.

Hydrogen Ions from Water The reaction in which water molecules produce ions is called the self- ionization of water.

In aqueous solutions: (Something dissolved in water) The concentration of H+ and the concentration of OH- multiplied together will equal 1.0  10-14. Concentration of H+ = [H+] Concentration of OH- = [OH-]

Neutral, Acidic, or Basic? When [H+] and [OH-] are equal, it is described as a neutral solution. An acidic solution is one in which [H+] is greater than [OH-]. A basic solution is one in which [H+] is less than [OH]. [H+] > 1.0 x 10-7 = acidic [H+] < 1.0 x 10-7 = basic

Calculation 1: Using H+ or OH- to find concentrations

Where does pH come into play? Use your hydrogen ion concentration to calculate the pH of your substance.

Relating pH to [H+] A solution in which [H+] is greater than 1  10–7 M has a pH less than 7.0 and is acidic. The pH of pure water or a neutral aqueous solution is 7.0. A solution with a pH greater than 7 is basic and has a [H+] of less than 1  10–7 M.

Calculation 2: Calculate pH from [H+]:

Calculation 3: Using pH to find [H+]:

Calculation 4: Calculating pH from [OH-]:

Acid-Base Indicators: An indicator is a valuable tool for measuring pH because its acid form and base form have different colors in solution.

Acid-Base Indicators: 1) Universal Indicators:

Acid-Base Indicators: 2) pH Meters:

Acid-Base Indicators: 3) Phenolphthalein changes from colorless to pink at pH 7–9. This indicator is used for TITRATIONS.

Assignment Complete Lab Use pH values to calculate the [H+] of each substance. Turn in when completed.