1. LABORATORY NOTEBOOK
In addition to the North Central College Laboratory Guidelines you should review these comments and references. Each student will have a bound notebook with NCR paper to record all observations and data. See pages 829 to 831 of the text, Fundamentals of Analytical Chemistry by Skoog, West and Holler for general guidelines concerning the laboratory notebook. A good way to finish each experiment is to summarize the experiment; this summary should include averaging the numerical data. Every experiment needs a verbal conclusion. All Students are required to use Excel [or another computer spreadsheet program] in the calculation and presentation of their data. Let your spreadsheet do your calculations.
2. LABORATORY RULES
2. When you complete your work for the day you are EXPECTED to clean up the area where you work. This includes washing the desk top, and leaving the Balance Room neat. All equipment that is left out will disappear. Also clean the hood area and put away hot plates.
3. Make sure that you label all flasks, beakers, and bottles -- This includes your name, contents and date. "Diamond Labels" or a sharpie are available for your use. Glass marking pens (sharpies) are convenient.
4. The laboratory will be open from 1:30 to 4:30 PM on your two lab days. All work should be completed during these hours. Any person can make a grade of A if they had all of the time in the week in the laboratory. PLAN your work carefully.
5. All fuming containers and bad smelling compounds should be handled under a fume hood with adequate ventilation. After using the hood, be sure to clean up the area where you worked.
6. Dress for laboratory should include comfortable clothes. (Remember that clothing worn to laboratory sometimes gets ruined.) Shoes are required of all persons in the laboratory. (Cut feet are NO FUN.)
7. No smoking is permitted in the Science Center.
8. Use care in the disposal of all chemicals.
9. Adhere to all of the
items in the North Central College Safety Contract.
2. Come to the laboratory well prepared in advance, having a definite plan for your work.
3. Keep your equipment, the working bench and the balance area immaculately clean. Dirty and sloppy work will inevitably reflect in faulty results and low grades. In analytical chemistry cleanliness is absolutely essential.
4. Practice with the reading of the burette and detecting end-points before you actually attempt the quantitative determination. Each experiment has to be run at least in triplicate. It is recommended that the student start with four samples so that one can be ruined and three will remain and be usable.
5. Record every step of your work in the laboratory notebook and carefully tabulate all experimental results as obtained. Attach computer printouts. Neat laboratory notebook indicates understanding. Loose paper has no place in the analytical chemistry laboratory.
6. Each laboratory period plan to calculate that day's results either before leaving for the day, or before the next laboratory period. PROMPT CALCULATION IS A GUIDE TO THE NEXT STEP IN THE LABORATORY! Many students report that after the calculations are done another set of samples is needed.
7. All samples for analytical
determination should be weighed on the analytical balance. Most reagents
are prepared using a top loading balance. The rule of thumb is to use the
analytical balance unless you will standardize the solution.
Each student is expected to work independently and to proceed at his (or her) own pace. The laboratory topics are listed so that you may gage your own pace and, if behind, speed up the minimal pace. The due dates are set ONE WEEK after the student should have completed the experiment. If the report is turned in after this date, a late penalty of 5% per laboratory period must be deducted from the student's grade on the report. All laboratory reports should be submitted according to the guidelines listed in that document. All percentage values must be to the hundredth of a percent, and all standardizations to four significant figures (i.e., 14.67%, 0.1011 M, or 0.09345 M). It is expected that the student will use the computer in all calculations. All reports must include a verbal conclusion or summary that includes the numerical values obtained. All reports are due at the end of lab on the date due. The good student should be able to work more rapidly than this schedule and should plan to turn in the report as the work is completed. If you have finished all of the laboratory work, you may check in your equipment and be excused from laboratory for the remainder of the term.
Each laboratory report (in the laboratory notebook) should include the following: title; objectives; procedure modifications (i.e. I used 200 ml vol. flasks instead of 100 ml. vol. flasks etc.); raw data [all weights (init, final and net); all volumes (init. and final if a burette), and size of containers]; calculated data with a sample calculation; average (show valid rejections) and deviation in ppt; computer print out; and conclusions. In your conclusions you should compare the results from the two methods, i.e., "I found the unknown had 55.55% Cl with 2 ppt dev by Gravimetric means (p.55) and 55.85% Cl with 1.1 ppt dev by the Adsorption Indicator method (p. 57). Therefore, I feel that my unknown chloride had between 55.55% and 55.85% Cl in it. I had good precision on both methods." would be the minimum. If you ended up with 55.55% Cl and 66.66% Cl, you should give some reason for the difference. Unknowns are graded on accuracy, precision, lateness (negative), and conclusions.
The student is expected to meet the laboratory objectives listed on the objective sheet. Each unknown after the unknown acid will be done by two methods. If your grade on a particular unknown determination is not satisfactory you may NOT repeat the determination, but you may do one or more alternate determinations from the list of experiments. Alternate experiments may be reported by only one method if the other half of a determination was satisfactory.
All unknowns must be requested the period before they are needed and none will be issued after the third hour test. In order to request an unknown you should place a beaker containing a clean, dry, labeled weighing bottle in the designated place. The instructor will then place the requested unknown in the oven before the next laboratory session. Each unknown request should include the student's name, and unknown requested.
5. PREPARATION AND USE OF EQUIPMENT
Clean and dry thoroughly all three pieces of the desiccator. Before wetting your desiccator check with Dr. Sherren. A paper towel of "Kim-Wipe" may be adequate to clean the dissector. Place about 50 ml. of dry Drite in the bottom of the desiccator. It should have a few blue lumps in it. If these lumps turn purple or pink, the drite should be dried over night -- see the instructor about this drying. Put in the porcelain plate. Cover the ground glass surfaces of the lid and the bottom with petroleum jelly, Vaseline, or some other grease. The desiccator is used for keeping materials dry, and it must be kept tightly sealed. See pages 788-789 for additional facts about desiccators and drying. (Page references are to Fundamentals of Analytical Chemistry by Skoog, West & Holler.)
Burettes enable you to measure the volume of liquids quite accurately; the 50-ml. burette is calibrated to the 0.1 ml. and the user is expected to estimate to the 0.01 ml. Burettes should be washed thoroughly with detergent solution (use a burette brush--the one with the L-O-N-G handle), rinsed several (at least 4) times with tap water, and then rinsed with distilled water. If when a "clean" burette is drained any drops of water cling to the inside walls of the burette, it is not clean enough for use. The glass stopcocks should be lubricated with stopcock grease so that they do not leak. When you fill a burette with a liquid to be measured, such as your acid or base solutions, you should first rinse it about 3 times with 10 or 15 ml. of fresh solution each time. Label each burette at the top so that you will use the same one for acid each time and the other one for base. Always remove the funnel used in filling the burette before reading the level of the liquid. See pages 803-805 of the textbook for more details. Note the picture on page 825.
The most important, and at the same time the most delicate instrument used in analytical chemistry is the analytical balance. The balance is used to measure small quantities of materials. A scale is used to measure large quantities. Directions for the use of the analytical balances and top loader balances used in this course will be given on the first day of the laboratory. Make sure that you are familiar with both the balances and the instructions. Be sure that your balance is level before beginning.
4. Weighing Bottles
Weighing bottles are used for weighing and storing samples. They should be washed, rinsed and oven dried thoroughly before using. The sample to be dried is then placed in the weighing bottle, which in turn is put in a small beaker, and this is placed in the oven at 100o-110o C. to be dried for at least 1 hour. The student should put his initials and a code for the contents of the bottle on the bottle in pencil -- NO LABELS. The beaker should have the student's name and the sample on it using a pen that writes on glass. Label tape and labels do not survive drying. When the sample is dry it should be transferred quickly to the desiccator with crucible tongs. The weighing bottle cover is kept sideways on the weighing bottle when the sample is drying in the oven and when in the desiccator. The desiccator lid should be left open a few seconds until the desiccator does not "pop". Then the lid should be closed tightly. See the text for more information, page 788. Always replace the desiccator lid. There is no quicker way to ruin results than to have poorly desiccated or wet samples.
Samples may be weighed any time after they have been dried and cooled. They may be stored in the desiccator several days, if necessary. In weighing, do not touch the weighing bottle with your bare hands. Always use tongs or a piece of KIMWIPE when handling it.
5. Deionized or Distilled Water
All glassware should be washed in tap water (hot if possible), with detergent, rinsed with tap water 3 or 4 times and then rinsed 2 times with deionized water. Use deionized water to make up all solutions unless the directions specifically call for another solvent. We have deionized water to use, but do not WASTE deionized water. NOTE: When you leave for the day check to see that the deionized water is not dripping. We do not have water savers on the deionized water (d.i. or d.w.) outlets and a slow drip will empty a 5-gallon bottle overnight. These directions also apply to distilled water.
6. Plastic For Covering Containers
After you have weighed out a sample in a flask or beaker, it is often necessary to let this sample stand until the next laboratory period. If you desire to cover the container and do not want any particles of cork, stopper, etc. to introduce an error in your analysis, plastic wrap of several types is provided for this use. The only items to be covered with plastic are those which have samples weighed into them and ready for the next period's use. The wrap is community property as are the scissors and neither should be removed from the south bench of the analytical chemistry laboratory. Rubber bands are available.
7. Community Equipment
There are a number of items of community equipment that is for your use, but are to be returned before you leave for the day. These items include pipette controls, tongs, label tape, plastic wrap, suction flasks and tubing, big burners, large graduated cylinders, and hot plates. I am sure there are other items besides the chemical reagents on the north wall of the laboratory. Volumetric flasks are an item which are used on the honor system -- when you need one get from the cabinet, use it, and when you finish wash it and distill water rinse it, oven dry it and then return to the cabinet. Always deionized or distill water rinse volumetric flasks to be sure they are clean (if it looks dirty also soap wash it). If you have questions please see the instructor.
8. GOOD PLANNING INCLUDES:
Thinking through the experiment; write the equations involved; question the reason for the addition of each chemical, and what happens if the chemical is omitted. A final step in planning would be constructing a block diagram or flow sheet for the determination. The instructor is available to help you with your questions.
Each student is expected to clean up his or her own mess. This includes: Washing the desk top at the end of the laboratory period; cleaning up the balance areas and returning all chemicals to the proper place. If a mess is made in the hood it is expected that area will also be cleaned. Equipment that is left out will disappear. All equipment returned to the back hall must be CLEAN! If a mess is made in the balance, call the instructor for cleaning directions.
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