Alternatively, some volumetric glassware bears the label " TD 20☌" which stands for " to deliver at 20☌." This means that at 20☌, precisely the volume listed will leave it when the contents are allowed to drain out of the vessel. If you were to pour out the liquid, you would need to get every drop out of it to have that volume. TC versus TD Some volumetric glassware bears the label " TC 20☌" which stands for " to contain at 20☌." This means that at 20☌, that flask will have precisely the volume listed inside it. View the meniscus at a level perpendicular to your eye to avoid this as a source of error. If your eye is above or below the level of the meniscus, your readings will be inaccurate due to the phenomenon of parallax. It is often easier to see the meniscus if you put a white paper or card behind the apparatus. To read this volume exactly, the bottom of the curved surface of the liquid, the meniscus, should be located at the scribed line for the desired volume. All volumetric glassware is calibrated with markings used to determine a specific volume of liquid to varying degrees of accuracy. More detail on how to do this will be given in the discussion of the individual pieces of glassware. This prevents water droplets from diluting one's solution, and changing the concentration. With some types of glassware, one "conditions" the apparatus by rinsing with a few small portions of the solution one will be measuring prior to conducting the actual work. If you are suspicious at all, wash it before you use it as well. Rinse your glassware thoroughly with deionized water when you are finished with it. Chemically clean glass supports a uniform film of water, with no hanging droplets visible. Cleanliness is essential to good results. These involve cleanliness and how to read volumes accurately. There are some points that are common to all types, however. These have specific uses and will be discussed individually. Four main types of volumetric glassware are common: the graduated cylinder, the volumetric flask, the buret and the pipet. Glassware designed for this level of accuracy and precision is expensive, and requires some care and skill to give best results. One can then report quantities greater than 10 mL to four significant figures. This involves using glassware that can contain or deliver a volume known to a few hundredths of a milliliter, or about 0.01 mL. Volumetric Glassware In quantitative chemistry, it is often necessary to make volume measurements with an error on the order of 0.1%, one part per thousand. 7 Obtain the mass of hygroscopic (water absorbing) materials quickly.
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