Introduction to the Chemistry 230 Laboratory

2. A laboratory notebook, which must be a bound quadrille ruled 10" x 7-3/4" composition notebook. It MUST not be a spiral bound notebook from which pages may be easily torn.

A total of 550 points can be earned in the laboratory portion of the course. A maximum of 100 points will be given for each of the five analyses, for a total of 500 points. Your grades will be based upon your accuracy, precision and acquired skills necessary to be a competent laboratory technician. Up to 50 are possible for the quality of the laboratory notebook when it is turned in at the end of the semester.

The number of points that will be awarded for the analytical results will depend solely on the accuracy of the reported results. The criterion for the accuracy will be the relative percent error. This value will be established from the experimental value and the "accepted value" which is the value determined by an independent, off-campus analytical laboratory.

For the standards expected for the laboratory notebook the student should refer to the section in this manual entitled "Laboratory Notebook".

At the time that you were issued a locker for use in CHE 230, you were asked to read and sign a "Chemistry Laboratory Safety" sheet. Strict adherence to all those rules is expected of all students both for their own and others' safety. In addition to the safety issues discussed on that sheet a few other safety related topics are discussed below.

The laboratory is equipped with chemical work benches which have water, gas, air and vacuum outlets. There are two ventilated fume hoods in which you can safely perform chemical procedures which liberate noxious gases and fumes. Top-loading balances for three decimal-place accuracy and four decimal-place accuracy analytical balances are located in the adjoining weighing room.

The chemicals for the analyses will be found on the reagent table at the front of the laboratory.

Never carry reagents bottles away from the table. Bring beakers, flasks or graduated cylinders to the table.

Take only the quantity of reagent specified in the directions. Measure the quantities as carefully as possible. Carefully read the labels on the bottles before you take a chemical.

Never dip a stirring rod or medicine dropper into a reagent bottle. Transfer a small quantity of reagent to a beaker take the required amount from there. Always replace the lid on reagent bottles after using them.

Never return reagents to reagent bottles after you have removed them. Dangerous contamination may result. This is particularly important in an analytical laboratory where the purity of substances is so crucial. Give any excess to other students or discard.

If you spill reagents, clean them up immediately. If necessary rinse well with water.

Keep your desk and reagent table clean and tidy at all times. At the end of the period, clean the apparatus and place it in your locker. Sponge off the top of your desk. Dispose of aqueous and water-soluble wastes in the sink. Dispose solid waste in the waste baskets.

Many chemicals or combinations of chemicals are potentially dangerous if handled carelessly. With proper precautions accidents can be avoided in the laboratory. Abide by all the above rules and those enumerated on the sheet on Chemistry Laboratory Safety which is supplied in your locker and a copy of which you signed during check-in.

If you should break an item of glassware be sure that you pick up all pieces of glass and discard them in the container marked "Broken Glassware". Do not, under any circumstances, discard them in an ordinary trash barrel or waste paper basket.

Do not place articles of clothing, big bags or unnecessary books on the lab benches. Use the coat-hanger rack on the west wall of the room to hang your extra clothing. Other items can be stored on tables provided for this purpose.

All entries in your notebook must be made with a non-erasable ink pen. Leave at least one blank page between different experiments. Be sure that you provide a proper heading for each analysis. In addition to this your laboratory notebook must have a Table of Contents, so be sure to set aside a few pages at the front of the notebook for this purpose. If the pages in your notebook are not already numbered it will be necessary for you to number all pages with an ink pen. Both sides of each sheet must be used except for the blank page between experiments. A bound "Comp Book", available in the bookstore, containing 80 sheets, 10 x 7-3/4", quadrille ruled with 5 lines per inch in each direction, is acceptable, but a spiral bound notebook is not acceptable . A notebook with extra sheets for copies to be made with carbon paper in between is not recommended for this course.

Orderliness in a notebook is advantageous. A little time spent before the laboratory period in planning and organizing is time well spent. Data should never be recorded in one portion of the book and later transferred to the proper page. This introduces the very real possibility of transcription errors. All entries must be made with a non-erasable ink pen.

In addition to raw data, all required calculations must be entered into the notebook. Calculations other than simple additions or subtractions should be done with a calculator. Since these display either more or fewer significant figures than are justified by the data, it is important that all results, of such calculations, be recorded with the correct number of significant figures.

Under no circumstances should any pages be removed from the notebook. If erroneous entries have been made, they should be crossed out using a single line in ink and a suitable annotation made, giving a reason for this action. If a single datum is changed, a line through the erroneous datum accompanied by the corrected value suffices. Where whole pages of data must be discarded a comment must accompany the crossed out section justifying the abandonment of those data. Do not use correction fluid, liquid paper, white-out or any product that covers up original entries.

Your laboratory notebook will not be collected until the end of the course. It will then be graded based on the criteria outlined above.

1. During the course you will be asked to make a variety of weighings. It is important for you to realize with what sort of accuracy these weighings should be made. Depending on the desired accuracy you should use the proper balance to make your weighings. There are two types of balances available to you in this course:

a. Top-loading balances. located in the room adjacent to the laboratory. These will weigh to an accuracy of ± 1 mg and are suitable for most weighings of amounts that are specified to only two or three significant figures. Directions for the use of these balances are posted in the balance room.

b. Analytical balances, also located in the room adjacent to the laboratory. These will weigh to an accuracy of ± 0.1 mg and must be used whenever you desire four or more significant figure accuracy. This will be the case when you weigh out samples of an unknown, primary standards or when taking crucibles to constant weight. Directions for the use of these balances are posted in the balance room.

2. When mass amounts are specified in chemical procedures the following terms are commonly used:

a. "Weigh out about 2 g of ...... " This statement means that you are required to weigh an amount of approximately two grams. The accuracy to which this mass amount needs to be known is not high and the top-loading balance will suffice.

b. "Accurately weigh out about 0.2 g of ...." This statement means that you should, with the aid of the analytical balance, weigh out an amount that is close to 0.2 g, but you must know the exact amount to an accuracy of ± 0.1 mg. Note that this does not mean that you must weigh out exactly 0.2000 g. An amount between 0.1900 g and 0.2100 g is perfectly acceptable. However, you must know the exact amount to the nearest tenth of a milligram. When weighing out triplicate samples it is not necessary that all three weights be exactly the same, indeed, it is poor procedure to attempt to do so.

The following rules summarize those procedures which must be followed in order to obtain accurate and reliable mass measurements with a single-pan analytical balance. Adherence to these rules will, at the same time, prevent damage to the balance.

1. Close the balance door, while weighing an object, in order to prevent air currents from disturbing the reading. When finished, the operator should close the balance door to prevent dust and dirt from entering the balance.

2. Only glass, ceramic, metal or plastic objects and containers should be placed in direct contact with the balance pan.

3. Do not handle objects to be weighed with bare hands. Moisture, grease and dirt on you fingers will affect the weight of the objects.

4. To be weighed accurately, all objects must be at room temperature. A warm object sets up convection currents inside the balance enclosure, which will make an object appear lighter than it really is. Also, warm air inside the enclosure is less dense than the air that it displaces and this also leads to a negative determinate error.

5. Never weigh chemicals directly in contact with the balance pan. Use containers such as beakers, flasks and weighing bottles.

6. All objects and materials that have recently been removed from a desiccator will absorb moisture and thereby gain weight. It is therefore good practice to record weights after identical time intervals. For example if you are taking crucibles to constant weight. Always record the weight of the crucible exactly 5 seconds after having placed the crucible on the balance pan. Using this technique it is possible to minimize the effect of moisture absorption.

7. The use of weighing paper must be strictly avoided when using an analytical balance.

8. Do not spill chemicals inside the balance enclosure. If a spill occurs, clean it up immediately. For additional instruction on the use of balances in the laboratory, click here.

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