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Liquid Level in the Distillation Flask

At the beginning of the distillation, the distillation pot should be between one-half full and two-thirds full. If the pot is too full, the surface area is too small for rapid evaporation and the distillation proceeds very slowly. If the pot is not full enough, there will be a large holdup volume and loss of sample. Holdup volume is the amount of vapor in the flask and head along with the liquid required to wet the inner walls of the apparatus. A typical holdup volume is one or two milliliters, which can lead to significant product loss, especially in a small-scale experiment. If you fill a flask and find it either too full or not full enough, choose another size of flask from your lab drawer.

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This flask is not full enough. This flask is too full. This flask is correct.

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