 |
 |
 |
 |
 |
 |
 |
 |
 |
The maintenance of a laboratory notebook is an important part of the General Chemistry Laboratory experience. Your laboratory notebook should be a clear and accurate record of your experiments and calculations as they happen. These written records of what transpires in the laboratory are critical to the practice of chemistry and other laboratory sciences. Thus, when you are done with an experiment and all of the chemicals used have been washed away, and all of the apparatus taken down, the notebook will serve as an infallible "memory" of what happened and how. In the real world, they constitute the basis for:
The
major question to keep asking yourself as you prepare a laboratory
write-up is this: have I provided sufficient detail so
someone else
can reproduce what I did in the laboratory AND get the same result
I did. Not so subtle threat: At some point during the
semester, your laboratory instructor will collect all notebooks at the
beginning of the period and randomly distribute them. You will be
required to run the lab from someone else's notebook. Do you
think someone could successfully run the lab from your notebook?
Laboratory notebooks are critical when unusual or unexpected results are obtained. Discoveries and inventions are extreme examples of unusual results. The acceptance of such findings by the scientific community generally depends on independent reproduction of the finding. A recent example of an irreproducible, unusual finding was the much publicized announcement of the production of large amounts of energy through "cold fusion".
Guidelines for keeping good notebooks:
There will be several other people in the lab and it is not always possible for everyone to have individual equipment. For example, several analytical balances are available. It is important to note which one is used in a weighing. It is important to note if different balances are used to determine initial and final weights. If more than one container of a reagent is available, is it important to note if samples of the same material are taken from different containers?
A student laboratory notebook should permit the determination of what step or steps in a procedure may have introduced discrepancies (e.g., when unknowns are involved, or when different results are reported on the same known material).
Information that each experiment should contain:
Each of these sections must be separate and labeled. You must have the experiment purpose and procedure written prior to the laboratory session for each experiment. Leave a little space in case the procedure must be modified from that found on the internet.
Laboratory Grade:
Your laboratory grade is
composed
of several components: lab reports, quizzes, and a final
exam.
Your overall lab grade represents 30% of your course grade.
Typically that
30% is broken down into two schemes: (20% from lab reports, 5%
from quizzes, and 5% from the final exam), or (25% from lab reports,
and 5% from the final exam). Your laboratory instructor will
inform you which grading scheme they will use.
Grading of the Lab Reports: Your laboratory report consists of the white pages from your notebook and is due at the beginning of the next laboratory period. Each report is worth a total of 100 points which will be distributed as follows:
Late reports will be accessed a penalty of 25% the first week, 50% the second week. If your report is three weeks late, you will receive a zero (0).
Attendance: Attendance at all laboratory meetings is required. If you find you can not attend a given lab then you will have to use it as your 'drop lab'. If you miss a second lab, a grade of zero (0) will be assigned.
|
|
|
|
|
|
|
|
|
|
|
|
Devices:
Ideally, when performing quantitative experiments, the devices used (e.g., balances, burets, pipettes, volumetric flasks, etc.) should be calibrated. In an introductory chemistry laboratory, time does not generally permit calibrating such devices.
Some types of errors will be minimized by consistently using the same device for the same type of measurement. Consider an extreme example.
A buret has been incorrectly, but consistently marked so that each major unit (mL) is actually 1.1 mL.. If the same buret is used to standardize a reagent solution and to titrate an unknown solution, the absolute error in accuracy caused by the incorrect markings will cancel. If the standardization is carried out using the inaccurate buret and a different, correctly marked buret is used in titrating the unknown, a 10% error in accuracy will result.
Whenever possible, a unique identifier of a device should be recorded. If the device does not appear to function as expected, a comment to that effect should be noted. If there is a significant malfunction, the attention of an instructor is mandated.
Reagents:
Again, ideally, the student investigator should prepare all the necessary reagents for an exercise. Preparing a reagent means noting the purity and assay of the starting materials and using the appropriate quantitative techniques for the preparation of solutions. In the introductory laboratory, stock solutions are often provided to save time. An individual student has little control over the quality of the reagents provided. Assuming that no one has changed the stock chemical in anyway, it should contain what its label indicates. At the very least, the laboratory notebook should indicate the data on the label of the stock solution (with the appropriate number of significant figures).
Other Materials:
In instances where the student provides some of the materials for an exercise, the identity of the material should be recorded in detail, along with any relevant data. For example, the following characterization of buffered aspirin tablets as it should appear in the notebook:
Trade Name: Bufferin
Manufacturer: Bristol-Myers Products
Type: Extra Strength - 500 mg Tablets
Ingredients: Aspirin buffered with Calcium Carbonate,
Magnesium Oxide, and Magnesium Carbonate
Lot Number: BLOJ1 EXP SEP 99
(Updated 8/16/08 by C.R. Snelling)