1. Determining pH and Titrations
Section 15.2

2. Acid-Base Indicators
acid-base indicators: compounds whose colors are sensitive to pH
Indicators change colors because they are either weak acids or weak bases

3. Indicators Indicators come in many different colors
There are specific pH ranges over which an indicator changes color
Transition interval: the pH range over which an indicator changes color

5. pH Meter and Paper
pH meter: determines the pH of a solution by measuring the voltage between the two electrodes that are placed in the solution
pH paper is used by comparing the color the paper turns when it is in contact with the solution

7. Titration
Titration: the controlled addition and measurement of the amount of a solution of known concentration required to react completely with a measured amount of a solution of unknown concentration

9. Equivalence Point
Equivalence point: the point at which the two solutions used in a titration are present in chemically equivalent amounts
Indicators and/or pH meters can be used to determine the equivalence point

10. More about Titrations
End point (of the indicator): the point in a titration at which an indicator changes color
Indicators that undergo transition at about pH 7 are used to determine the equivalence point of strong acid/strong base titrations

12. Standard Solution
Standard solution: (AKA known solution) the solution that contains the precisely known concentration of a solute
See pages in the book at school for the procedure for carrying out an acid-base titration (pages in your book at home)

13. Sample Problem for a Titration
Suppose that 10.1 mL HNO3 is neutralized by 71.4 mL of a 4.2 x 10-3 M solution of KOH in a titration. Calculate the concentration of the HNO3 solution.
Step 1: write and balance the equation.
HNO3 + KOH  H2O + KNO3

14. Problem Continued
Step 2: define what you are given in the units required
V of KOH = 71.4 mL = L
[KOH] = 4.2 x 10-3 M
V of HNO3 = 10.1 mL = L
[HNO3] = ?

15. Continued Step 3: find the mol of the known volume
Mol = [ KOH] (volume in liters)
Mol = 4.2 x 10-3 mol/L KOH  L
Mol = x 10-4 mol KOH
Step 4: find the mol of the unknown (HNO3)
x 10-4 mol KOH  1 mol HNO3 / 1 mol KOH
x 10-4 mol HNO3

16. Continued Step 5 calculate [unknown]
x 10-4 mol HNO3 / L =
3.0 x 10-2 M HNO3

17. Calculations
See pages in the book at school and pages in the book at home for sample calculations