Calibration of Volumetric Glassware
This set of laboratory experiments is designed to introduce you to some of the apparatus and operations you will be using during the remainder of this course, including the treatment of data using spreadsheets. While some of the procedures may seem trivial and the results obvious, this is a chance for you to develop good laboratory technique. Required Reading
D.C. Harris, Quantitative Chemical Analysis (8th ed., W. H. Freeman, NY, 2010) chapter 2 (Tools of the trade)
Electronic Balances (including Weighing by Difference), Analytical Lab Manual. Burettes, Analytical Lab Manual.
REAGENTS AND APPARATUS
• Analytical Balance
• 400 mL beaker
• 3 - 2 oz. plastic bottles with caps
• 5 mL volumetric pipet
• 100 μL Eppendorf micropipet
• distilled, deionized water
• 2 , 50 mL burets
PART A - USE OF THE ANALYTICAL BALANCE
The analytical balances in the lab are probably the most precise, accurate and reliable pieces of equipment that you will use during the semester. To understand how these balances operate and
their limitations you should read the appropriate section in your textbook. Although there are inherent limits in the accuracy and precision of these balances most weighing errors are caused by incorrect handling of the sample. In the first part of this lab you will investigate several potential sources of error.
1. In this section you will determine the mass of a clean, dry weighing bottle under various conditions. Unless instructed otherwise, you should handle the bottle with your crucible tongs, gloves, or lint-free paper and measurements should be made to the nearest 0.1 mg. Begin by placing the weighing bottle and cap (with cap removed) in the oven for about 5 minutes. Remove and re-mass while warm. Follow the change in its apparent mass for several minutes, reweighing every thirty seconds. Record all masses including the final constant value. 2
2. After massing the weighing bottle, roll it around in your hand (handle the bottle with your fingers) and then re-mass and compare the two masses. How should weighing bottles be handled on a regular basis?
3. Next, wipe the bottle clean with a dry, lint-free cloth or tissue and reweigh. Record all observations.
4. Hold the weighing bottle and inch from your mouth and breathe on it several times. Re-mass and compare with previous data.
5. Discuss your results in your laboratory write-up.
PART B- CALIBRATION OF VOLUMETRIC GLASSWARE
Throughout the semester, you will be required to make accurate measurements of volume. The primary means of doing so will be by using either a volumetric pipet, a Mohr pipet, a micropipet, or a buret. Many manufacturers calibrate their glassware so that the true volume is within specified limits of the labeled volume. In cases where particularly accurate measurements are needed, it may be necessary to make a more accurate calibration of your volumetric containers. In this experiment you will calibrate a buret, a volumetric pipet, and a micropipet. PROCEDURE
In order to prevent difficulties with access to the analytical balances, please perform all pipetting and volume measurement manipulations at your normal lab station, then transport the bottle to the analytical balance to mass it.
1. If you have any questions concerning the use of any of the volumetric glassware necessary for the experiment, be certain to refer to Chapter 2 in your textbook. Additional information can be obtained from your instructor. A summary of the calibration techniques are provided on pgs 43 (pipet) and 49-50 (buret).
2. Place about 250 mL of distilled, deionized water in a 400-mL beaker. Place a thermometer in the beaker containing the water and leave it in place through the remainder of the experiment. If the temperature of the water is not identical to that of the room temperature, allow the water to equilibrate to room...
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