Molecularity: Who Has the Same Substance?

Work in pairs. Complete a Preparation page before each laboratory period.

Goals

 Background

The purpose of this project is to give you a long-term, research-like laboratory experience in chemistry. Unlike the 1-period experiments that you have performed during previous terms, this project will occupy the entire term, and will be conducted at your pace and according to your experimental decisions. Instructors will be on hand to provide help and guidance; however, the responsibility for advancing the project to a meaningful conclusion will be yours.

Before coming to lab each week, you should complete the appropriate set of Preparation Questions and hand them in at the beginning of the period, as usual. We expect that you will maintain your laboratory notebook in the same manner as in previous terms; however, the notebook will not be turned in for grading. Instead, you will be expected to submit a formal research report on your findings at the end of the term. Your laboratory grade will be based on the quality of this report, and on the Preparation Questions that you answer each week.

A key activity of the chemist is to establish the structural personality of a newly synthesized substance by determining an array of physical and chemical properties of the substance. These properties are then associated with the substance and can be used to identify it. They all reflect in some way the structure of the substance at the molecular level.

With a new substance in hand, the chemist might first establish the very simple physical properties such as color, crystalline form (for solids), and melting point (for solids). S/he might then proceed to explore simple chemical properties. For example, is the substance an acid (reacts with base, or turns litmus red) or a base (reacts with acid, or turns litmus blue)? Finally, the modern chemist will elucidate the spectroscopic properties of a substance by obtaining its infrared spectrum, electronic absorption spectrum, and nuclear magnetic resonance spectrum. These spectra reflect the manner in which various molecular motions interact with light, and provide information about the bonding patterns and arrangements of electrons in molecules.

Description of Project You will work with one or more partners throughout the term. At the first lab period, you and your partners will be given a vial containing a small quantity of a pure substance. Your overall goals are to identify and characterize your substance, and to find out what other teams in the class have the same substance. You can accomplish this by addressing, during the successive weeks of the term, the following project objectives:

Focus Questions

Equipment and Materials

Preparation Questions

  1. Week 1
  2. Week 2
  3. Week 3
  4. Week 4
  5. Week 5
Safety

Safety glasses must be worn at all times in the laboratory. You will use mercury thermometers. Mercury is an extremely toxic substance. Report thermometer breakage IMMEDIATELY to your instructor, who will take the necessary steps to clean up the mercury spill. Other safety matters depend on the design of your experimental procedure. The instructor will discuss safety with you once your procedure has been approved.

Experimental

Please print and read the documents dealing with fundamental laboratory operations and procedures:

Record all data in your notebook. Express your identification procedure as a flow chart and discuss it with the instructor. Then carry out your procedure in the laboratory, and determine who else in the lab has the same substance that you have. Identify as many structural features of a molecule of your substance as you can.

As you proceed, post each new property of your substance so that other students may readily read the posting for comparison. When you believe you have found at least one other student pair having the same substance, team up and spectroscopically characterize your two substances.

Design of experiments is up to you. Please keep in mind that we have available supplies of all the substances used for the unknowns. You are free to use these for comparison tests if and when you think these would be useful.

Clean-up. When you have finished all of your work each week:

Disposal Methods

Dispose of all solids, liquids, and solutions in the appropriately marked waste bottles.

Some Guidelines and Cautions

Guidelines

  1. At the beginning of each laboratory session except the 6th one, you are to turn in your answers to the appropriate set of Preparation Questions. Each set of Preparation Questions is valued at 8 points, for a total of 40 points for the 5 sets.
  2. You have six 3-hour lab periods in which to complete the project. This is 18 hours, or just a little more than 2 full working days! You should make an overall plan listing which experiments you will attempt each week. In addition, you should make a detailed plan for each laboratory period, designed to make your use of time as efficient as possible. We will not collect or grade these plans, but unless you formulate them, you will not make much progress.

    We suggest that you plan to complete the experiments up to and including Thin Layer Chromatography by the end of the second lab session.

  3. You TA will maintain a time/activity log during the term. For each laboratory session, you should enter
  4. Midterm Progress. Using the prescribed format, you must submit a partial to-date preliminary version of your Formal Research Report for review following the third lab session. This preliminary version will not be graded; instead, it will be treated as a draft and will be critically reviewed and critiqued. The preliminary version must be submitted NO LATER THAN NOON on the Friday following your third lab session.
  5. Your final Formal Research Report is due NO LATER THAN noon on the Monday of the final week of C term.

Cautions

  1. Because you will be doing on-going research this term, rather than a series of 1-week, independent laboratory experiments, it is essential that you be well-prepared for every lab session and that you keep detailed records of experimental procedures, observations, and results in your laboratory notebook. THE NOTEBOOK WILL NOT BE SUBMITTED FOR GRADING. IT IS STRICTLY FOR YOUR RECORDS; IN IT SHOULD BE ALL OF THE INFORMATION REQUIRED FOR THE WRITING OF YOUR FINAL REPORT. BE FASTIDIOUS AND THOROUGH IN MAINTAINING YOUR LAB NOTEBOOK.

  2. Because you will be working with the same partner(s) for the entire term, it is important that you not casually miss any laboratory periods. Doing so has a strong impact on your partner(s).