1. © University of South Carolina Board of Trustees Determine the number of moles of Na(CH 3 COO) that must be added to 250 mL of 0.16 M CH 3 COOH to prepare a pH 4.70 solution. K a = 1.8x10 −5 pH  Buffer composition

2. © University of South Carolina Board of Trustees Student Example How many millimoles of NaCN should be added to 100 mL of 0.25 M HCN to prepare a buffer with pH = 9.40? K a = 4.9x10 −10.

3. © University of South Carolina Board of Trustees Does a Buffer Stabilize pH? Calculate the initial and final pH when 10.0 mL of 0.100 M HCl is added to: (a)100 mL of water (b)100 mL of a buffer which is 1.50 M in CH 3 COOH (p K a = 4.74) and 1.25 M in Na(CH 3 COO) pH 7.00 pH 4.66  4.65  4.65  2.04  2.04

4. © University of South Carolina Board of Trustees Chapt. 16 More Acids and Bases Sec. 1 Titration: Chemistry Unplugged

5. © University of South Carolina Board of Trustees Titration Experiment acid solution unknown concentration strong base solution known concentration indicator dye changes color record volume of base

6. © University of South Carolina Board of Trustees Titration Overview (Strong Acid + Strong Base example) Titration Curve: a graph of pH of the solution in the flask as titrant (base) is added.

7. © University of South Carolina Board of Trustees Titration Overview (Strong Acid + Strong Base example) Equivalence Point: (known) moles of base added equals (unknown) moles of acid in sample.

8. © University of South Carolina Board of Trustees Titration Overview (Strong Acid + Strong Base example) Indicator: Added dye that changes color at the equivalence point. color change

9. © University of South Carolina Board of Trustees Classroom Titration Problem The equivalence point in the titration of 20.00 mL of ??? M HCl with 0.1008 M NaOH is at 24.84 mL. What is the concentration of the HCl? What is the pH of the equivalence point?

10. © University of South Carolina Board of Trustees Titration Overview (Strong Acid + Strong Base example) Equivalence Point: (known) moles of base added equals (unknown) moles of acid in sample. pH volume of NaOH

11. © University of South Carolina Board of Trustees Real Titration Problem A solution of ascorbic acid has an unknown concentration. A small amount of phenolphthalein (indicator) is added to 25.00 mL of the solution, and it is titrated with 0.100 M NaOH. The first pink color is seen when 18.12 mL of NaOH solution has been added. What is the concentration of ascorbic acid in the original sample?