Measurement of Volume and Weight

Special care must be taken when working with small amounts of liquid or solids. In the typical microscale experiment, a student will use from 10 to 1000 mg of a liquid or solid. Specially designed microscale equipment will be used for these small-scale reactions. You may not be used to working with such small quantities, but after a while you will adjust to thinking small.  

Careless dispensing of liquids and solids is a hazard in any laboratory. When reagents are spilled, you may be subjected to an unnecessary health or fire hazard. In addition, you may waste expensive chemicals, destroy balance pans and clothing, and damage the environment. Always clean up any spills immediately. 

In most cases, the instructor will adjust the pipette so that it will deliver the desired volume. It will be placed in a convenient location near the reagent bottle, usually in a hood, and students will reuse the tip. Your instructor will give directions for the correct use of the automatic pipette. Students must practice using the automatic pipette. Remember that the automatic pipette is expensive and must be handled carefully. To protect the unit, you must always use a tip on the end of the pipette. Liquid must be drawn only into this plastic tip and never up into the unit itself. If this happens, you should notify your laboratory instructor immediately. Keep the pipette upright and immerse the tip just below the surface of the liquid. Automatic pipettes should never be used with corrosive liquids, such as sulfuric acid or hydrochloric acid. 

Dispensing pumps may be used in place of automatic pipettes when larger amounts (more than 0.1 mL) of liquids are being dispensed in the laboratory. The pumps 

As you pull up the plunger, look to see if fhe liquid is being drawn up into the pump unit. Some volatile liquids may not be drawn up in the expected maimer, and you will observe an air bubble. Air bubbles are commonly observed when the pump has not been used for a while. The air bubble can be removed from the pump by dispensing and discarding several volumes of liquid to reprime the dispensing pump. Also check to see if the spout is filled completely with liquid. An accurate volume will not be dispensed unless the spout is filled with liquid before you lift up the plunger. 

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Review Introduction to Microscale Laboratory (Experiment 1) Technique 8 Filtration, Sections 8.1-8.6 Technique 9 Physical Constants, Melting Points New Technique 5 Measurement of Volume and Weight... 

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