Chemistry 153 ? Laboratory Introduction - Lower Columbia College

Chemistry 153 - Laboratory Introduction
Chemistry 153 laboratory consists of an introductory exercise and
experiments selected to demonstrate a variety of chemical concepts,
analytical instruments, and laboratory techniques. Preparation for
laboratory exercises will require more time in Chemistry 153 - many of the
written procedures you follow during an experiment will be of your own
creation, synthesized from information in this manual, outside reading, and
lecture/laboratory discussion. Your complete record of each experiment,
including the written procedure, will be entered into your laboratory
notebook, described in the next section. The lab notebook will be your
only reference source while you are in the laboratory.
The Laboratory Notebook Your laboratory notebook is a complete record of your work in Chemistry 153
laboratory. It is used to write out experimental procedures prior to
beginning experiments, to record observations and data in the laboratory,
to complete all calculations, and to report the results of each experiment.
All written work connected with Chemistry 153 laboratory must be done in
your notebook. The laboratory notebook must be permanently bound, not
loose leaf or spiral. The pages should be lined (or graph) and preferably
numbered. If you purchase a notebook with unnumbered pages, you must
number each page. Notebooks must be done in ink, not pencil. Record data directly in your
notebook, never on loose pieces of paper for later transcription. If an
incorrect entry is made, it should be crossed out with a single line which
does not obliterate the entry, and the correction made next to or above the
crossed out entry. Never write over a number; later it may be impossible
to determine which number was correct. Do not crowd data in your notebook;
entries should be well spaced and clearly labeled. Pages should never be
torn out of a scientific notebook; if you wish to have a page disregarded
draw a single diagonal line across it. Save the first few pages of your notebook for a Table of Contents and keep
it up to date. As you prepare your notebook, allow sufficient pages for
data, calculations, and summary of results. The report must be placed on
the right hand pages only. Do not use the left hand pages as scratch
paper. Blank left hand pages allow a convenient place for data if the
experiment must be repeated. Finally, you should date procedure sections
and data as these entries are made in your notebook. Each experiment in your notebook should have six sections described below. 1. Title of the Experiment 2. Purpose A brief statement of the purpose of the experiment. 3. Procedure This is a step-by-step account of every operation in the
experiment. It should be detailed enough that the entire experiment
can be carried out without using other sources; it should be your only
reference in lab during the experiment. A balanced equation should be
included for any step which involves a chemical reaction. 4. Data All measurements and other observations should be directly
recorded in this section. Where possible, data should be tabulated
for easy future reference. In all cases, data must be clearly labeled
so their meaning will be obvious to any reader of the notebook. Also
be sure to date all data entries in your notebook. The three sections above and tables for entry of data must be completed
before work on an experiment begins. 5. Results In this section, the final results are calculated from the
experimental data. For experiments involving quantitative analyses,
results for each individual determination as well as a mean and a
relative standard deviation are computed. For each type of
calculation, a sample calculation, using your measured data, should be
given in detail including proper significant figures and units for all
numerical quantities. Finally, the identifying number of your unknown
should be clearly given in this section. 6. Data and Results Summary The final page(s) of the report will be used
to summarize selected data, sample calculations, and all experimental
results. Excel Data and Results Summary sheets will be distributed by
your laboratory instructor. After grading, these summary sheets are
to be taped into your laboratory notebook at the appropriate location,
so leave ample space between experiments for this purpose.
Laboratory Grading The experiments will be worth 85 points total toward your final Chem 153
lab grade. The maximum points for each experiment are below: |Exp. |Title |Points|
|1 |Nickel Exercise |10 |
|2 |Freezing Point Depression / Colligative Properties |20 |
|3 |Kinetics II: Determination of the order of a reaction. |20 |
|4 |Kinetics III: Determination of the order of a reaction. |40 |
| |Formal Report | |
|5 |LeChâtelier's Principle |20 |
|6 |Qualitative analysis |20 |
|7 |Water Hardness |20 |
|8 |Extraction and Precipitation Analysis of DNA (FORMAL |40 |
| |REPORT) | |
| |Laboratory Notebook |10 |
|Total |200 |
Your instructor will collect and review your laboratory notebook at the end
of the quarter. The instructor will also determine the weight of the lab
grade toward your final course grade. The standards used in grading experiments vary. Experiment 6 involves
correct identification of two unknowns. Correct determination of the
unknown is a large portion of your grade. Experiment 7 involves
quantitative analysis of an unknown sample in which the accuracy and
precision of results are expected to be high. This experiment will be
graded primarily on accuracy of your mean result and the precision of your
set of individual results. The grading scale for that experiment as points
deducted from the maximum of 20 points is given below. Although the other
experiments involve quantitative measurements and calculated results, the
accuracy and precision are not expected to be as great, and the grading
scale will be adapted accordingly. In all experiments, the quality and
completeness of the experimental write-up as well as results will be
considered in grading.
GRADING SCALE FOR CHEM 153 LABS |Accuracy |Precision |Other Factors |
| | | |
|Relative Error |Relative Standard Deviation|0.0 - 2.4 |-0 pt|
|(ppt) |(ppt) | | |
|0.0 - 1.9|-0 pt |2.5 - 3.9 |-1 pt |Reporting only two |-2 |
| | | | |results |pts |
|2.0 - 2.9|-1 pt |4.0 - 6.9 |-2 pts | | |
|3.0 - 3.9|-2 pts |7.0 - 9.9 |-3 pts |Reporting only one |-8 |
| | | | |result |pts |
|4.0 - 5.9|-3 pts |Over 9.9 |-4 pts | | |
|6.0 - 7.9|-4 pts | |Repeat Calculations or |-1 pt|
| | | |Incorrect Significant | |
| | | |Figures | |
|8.0 - 9.9|-5 pts | | | |
|10.0 - |-6 pts | | | |
|11.9 | | | | |
|12.0 - |-8 pts | | | |
|14.0 | | | | |
|Over 14 |-10 pts| |Repeat Experiment |-1 pt| The objectives of the first meeting of Chemistry 153 laboratory are . orientation to the laboratory and discussion of laboratory safety.
. laboratory check in.
. completion of an exercise which demonstrates the relationships among
precision, accuracy, and grading of Chem 153 experiments.
THE NICKEL EXERCISE Chemistry 153 Laboratory
Lower Columbia College INTRODUCTION Recall that precision refers to the closeness of a set of values obtained
from identical measurements of a quantity, whereas accuracy is defined as
the closeness of a single measurement to the true value. In most
experimental work, it is easy enough to determine the precision of a set of
measurements simply by repeating the measurement several times. Generally
the accuracy of those measurements is unknown; after all, if we knew the
true value of the measurement, we would be spared the bother of doing the
experiment at all. In the exercise below, however, we will have the
unusual situation in which the true value is assumed to be known. The exercise to be completed involves a series of weighings using the
analytical balances. These balances have a capacity of about 100 grams and
measure mass to +0.1 mg (±0.0001 g). As with any precision instrument,
care is required:
. never put chemicals directly on the balance pan,
. always place objects on the pan gently,
. be sure objects to be weighed are at room temperature,
. do not lean or place objects on the balance table,
. be sure all doors are closed when making final mass readings, and
. keep the balance area neat and clean. When several samples are needed for an analysis, weighing by difference is
often convenient. First a bottle containing a substance is weighed. Then
some of the substance is transferred to a conta