B Measuring Volume

Volumes of liquids or gases are measured by using glass or plastic apparatus that have been calibrated to read in units of volume as shown in FIGURE B.l. Certain apparatus such as graduated cylinders, volumetric flasks, and some pipets are designed to contain a specific volume of liquid when filled to the appropriate calibration mark. Other apparatus such as burets and some pipets are designed to deliver a specific volume of liquid into another container. 

The most important prerequisite for using volumetric apparatus is that it always be cleaned thoroughly before use by scrubbing with a brush and soap or detergent solution and rinsing carefully first with tap water and then with distilled water. The apparatus should then be allowed to dry or should be rinsed several times with a few milliliters of the liquid to be used, draining each portion completely between rinses. If the apparatus is clean, liquids will form a continuous film on the apparatus and will drain completely from the apparatus. However, if the apparatus is dirty, liquids will not wet the surface uniformly and will not drain completely from the apparatus. Droplets adhering to dirty surfaces can cause considerable errors in your volume measurements. 

To transfer this measured volume of liquid quantitatively to another container, pour by inverting the cylinder, and hold it in an inclined position for 15 seconds to allow it to drain 0. Remove the last drop from the lip of the cylinder by touching the lip to the inner wall of the receiving container.  

Burets are long, narrow, finely graduated tubes as shown in FIGURE B.l. They are designed to deliver precise and variable volumes of liquids into other containers. A stopcock or pinch clamp at the base of the buret provides for release of volumes between about 0.05 mL and the total volume of the buret. Burets are especially useful for adding solutions stepwise in small increments. Burets typically have uncertainties of about 

Volumetric flask. Volumetric flasks are used to contain precise volumes of liquids at a specified temperature. They are usually pear shaped and flat bottomed and have a long narrow neck with a single calibration mark as shown in FIGURE B.l. They are always used when standard solutions of precise concentration are being prepared. They typically have uncertainties of about +0.1%. Thus, you might measure 10.00 + 0.01 mL in a lO-mL volumetric flask or 100.0 + 0.1 mL in a 100-mL volumetric flask. 

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