Che 112

Name ___________________________________________Date experiment performed ________________________CRN of lab section: _______________________________ | Grade: ______________Days late: ____________Instructor Initials: _____ |

General Grading Items | 25 Points | Attendance at Pre-lab Meeting | /10 | Copies of lab pages attached; labeled with name and date, complete information, readable, data recorded matches results given in report | /5 | Waste was properly disposed of and lab area was cleaned | /5 | Evaluation of student performance overall (student was on time, followed safety rules, performed the lab correctly and within the time allowed, etc) | /5 | Total for General Grading Items | /25 |

Data Analysis and Interpretation Part | 75 Points | Titration Curves | /25 | Question 1 | /15 | Question 2 | /15 | Question 3 | /20 | Total for Data Analysis and Interpretation | /75 |

Data Table | Buffer A | Buffer B | Mass of NaC2H3O2 used to prepare buffer (grams) | | | Volume of buffer prepared (mL) | 100.0 | 100.0 | Molar concentration of HC2H3O2 in buffer (M) | 0.1 | 1.0 | Initial pH of buffer | | | Volume of 0.5 M NaOH to raise pH by 2 units (mL) | | | Volume of 0.5 M HCl to lower pH by 2 units (mL) | | | Volume of 0.5 M NaOH at equivalence point (mL) | | |

Data Analysis 1. Write reaction equations to explain how your acetic acid-acetate buffer reacts with an acid and reacts with a base.

2. Buffer capacity has a rather loose definition, yet it is an important property of buffers. A commonly seen definition of buffer capacity is: “The amount of H+ or OH– that can be neutralized before the pH changes to a significant degree.” Use your data to determine the buffer capacity of Buffer A and Buffer B. (Graphically, we can identify buffer capacity by the sudden change to a very steep slope.)

3. Say, for example, that you had prepared a Buffer C, in which you mixed 8.203 g of sodium acetate, NaC2H3O2, with 100.0 mL of 1.0 M acetic acid.

a. What would be the initial pH of Buffer C?

b. If you add 5.0 mL of 0.5 M NaOH solution to 20.0 mL each of Buffer B and Buffer C, which buffer’s pH would change less? Explain.