Calibration of Volumetric Glassware
Read: Chapters 1-4 in Harris to be prepared for the laboratory experiment.
This experiment is designed to introduce you to proper analytical laboratory techniques and to the methods for evaluating analytical data. As an analytical chemist, it is imperative to gather the best possible data from your equipment. Therefore, it is important to use all equipment correctly, patiently and precisely. In addition, a good analytical chemist will calibrate an ”instrument” before they use it to assure that the data gathered is as accurate as possible.
General Guidelines for the Analytical Laboratory
1. Never assume any glassware is clean unless you washed it yourself!!! 2. Keep your bench area clean!
3. Clean all glassware with soap and tap water unless otherwise directed. 4. Use distilled water to rinse your glassware, preferably a double or triple rinse. 5. Glassware that will not come clean in soap and water should be cleaned by soaking in a solution of 1 M Nitric Acid or 1 M KOH in alcohol, followed by a soap and water wash and distilled water rinse. This is typically true of burets. 6. Never heat any piece of volumetric glassware. Heating will cause changes in the glassware that will cause it not to be volumetric anymore ( 7. All items in this laboratory will be massed using the analytical balance. These balances read to the nearest 0.1 mg (0.0001 g). Thus, all masses recorded must be to the nearest 0.1 mg. (Do not record anything from the balance with out all 4 places) 8. You will be assigned a balance to use. You will use the same analytical balance for all measurements throughout the semester. This improves the precision of your measurements. (Plus I know who to penalize when it is trashed!) 9. YOU MUST CLEAN THE ANALYTICAL BALANCE WHEN YOU ARE FINISHED WITH IT! Failure to do so will result in a 5 point deduction from the laboratory reports of all the students assigned to that balance. 10. Burets must be washed at the end of every laboratory period (soap, water, rinsing with distilled water). Burets should be placed in the buret holder to drain—UPSIDEDOWN, with the stopcock open (MAKE SURE YOU INTIAL YOUR BURET). 11. Label all your glassware (on the glassware itself) as you use it and you should write the labels in your notebook so that you can keep track of what sample goes with what piece of data. 12. Refer to guidelines about keeping a notebook and writing a report in the ACS format.
Use and Calibration of a Pipet
1. Record the temperature in the laboratory (remember significant figures, there are divisions on the thermometer!) 2. Obtain a 10.00 mL volumetric pipet (there may be one in your drawer.) 3. Clean the pipet so that no droplets of distilled water are left on the inside of the surface as it drains. Alcoholic KOH might be needed. 4. Clean and dry (with paper towels) a small sample bottle with cap. 5. Avoid touching the flask/bottle with your hands as fingerprints and oils from your hands will cause imprecision in the recorded masses. You may use Kimwipes to do this. 6. Weigh the bottle to the nearest 0.1 mg
7. Place the bottle on a clean, dry surface at your work station. 8. The proper procedure for the use of a pipet appears in your textbook on page 27-28. A few rules apply: a. Clean the pipet as directed
b. Avoid sucking liquid into the pipet bulb as this causes contamination c. USE YOUR INDEX FINGER TO REPLACE THE BULB FOR DISPENSING. DO NOT UNDER ANY CIRCUMSTANCES USE YOUR THUMB!!! You cannot hold the pipet perfectly level for proper reading of the meniscus if you use your thumb. If I see you use your thumb, I will correct you. Even if it feels funny, relearn to do it the right way. d. You should always rinse the pipet with the solution you are pipetting and throw away the rinsing solution. e. Read the...
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