Procedures    

USE THE EQUIPMENT PROVIDED IN THE MANNER IN WHICH IT WAS INTENDED.

If you have questions about the appropriate piece of equipment to use, ask your instructor.

 

Fundamental Procedures

Techniques
Frequently poor results in a chemistry experiment are the result of poor laboratory technique. Technique is not a magic operation, but rather an orderly reasonable approach to a problem. Using good technique will prevent chemical contamination (mixing), the loss of precipitates, spilled liquids, and the like. Most importantly, it can prevent serious injury.

To consider the most important first: One must be considerate of his/her fellow worker in the laboratory because the nonreplaceable eyes are particularly susceptible to permanent damage. Always think of the consequences of the unpredictable accident; be cognizant of the direction of the force of your reaction if it does fail.

Remember your own best personal protection comes in the form of safety goggles and accident insurance. Another point of consideration to your fellow student and instructor is to use the hood when necessary. Vapors can be not only temporarily unpleasant but harmful to the lungs and membranes in the respiratory system. [See Safety Section for further cautions.]

Basic techniques are given for instructional and illustrative purposes as well. All operations cannot be covered here, but one should be able to develop other techniques on his/her own as necessary.

Obtaining a liquid from a bottle
To obtain a liquid from a bottle, grasp the stopper between the third and fourth fingers, with palms up, and while holding the stopper in this fashion pour from the bottle. Replace the stopper when finished. NOTE: The stopper never reached the dirty counter top nor touched the side of the bottle.

Obtain liquids in a clean dry beaker---not a test tube or graduated cylinder. Do not put pipettes or medicine droppers into reagent bottles. Do not take reagent bottles to your desk. Do not take more material than is required, for many of the chemicals used in the laboratory are costly, and disposal of excess chemicals is not only expensive, but bad for the environment. When carefully transferring liquids, pour the liquid down a stirring rod held across the top of the beaker from which one is pouring.

NEVER RETURN UNUSED LIQUIDS TO THE REAGENT BOTTLE: Place them in a container as designated by your instructor for proper disposal of the liquid or, if so instructed, flush them down the laboratory sink using a large quantity of water.

Measuring liquids
Graduated cylinders and pipettes are two commonly used pieces of lab equipment used for measuring volumes. Study carefully the particular piece of apparatus you are to use to determine how it is calibrated and the accuracy with which your measurements should be recorded on your data sheet. (If you do not know how accurate the equipment is, ask your instructor.) When reading the level of liquid in any liquid measuring device (graduated cylinder, pipette, burette, volumetric flask), read the bottom of the meniscus.

Obtaining solids from a bottle
To obtain a solid, unscrew the cap or remove the cork or stopper and place it upside down on the counter. Rotate and tilt the bottle at the same time to dispense the solid slowly to a weighing boat or a clean dry beaker. NOTE: No dirty spatulas were placed in the chemical and the stopper did not become contaminated from a dirty table top.

Do not take reagent bottles to your desk. Do not take more material than is required for many of the chemicals used in the laboratory are costly, and disposal of excess chemicals is not only expensive, but bad for the environment.

NEVER RETURN UNUSED SOLIDS TO THE REAGENT BOTTLE: Place them in the container designated by your instructor or, if so instructed, in the waste crock.

Use of the balance
Keep the balance clean. Always zero the balance before each weighing. Use a beaker or weighing boat instead of placing chemicals directly on the balance pan. Recheck to confirm that the balance is still zeroed after weighing.

Use of the thermometer
Laboratory thermometers are not to be shaken. Immerse the bulb of the thermometer in the substance for which you are to measure the temperature, allow the mercury level to stabilize and read the thermometer. Be sure to study the calibrations on the thermometer to determine how accurately it can be read. Do not use a thermometer as a stirring rod for stirring solutions. Remember, the bulb of the thermometer is delicate and mercury is very toxic. If a thermometer breaks, immediately inform your instructor, who will assist you in properly disposing of the mercury.

Heating liquids
When heating liquids in test tubes, always point the open end of the test tube away from yourself and other people. When heating liquids in beakers, stir the liquid while carefully heating to avoid bumping (uneven boiling which causes the dangerous spattering of large quantities of hot liquid).

 

 

 

 
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