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1.2F: Drying Glassware

  • Page ID
  • Quick Drying

    If dry glassware is not needed right away, it should be rinsed with distilled water and allowed to dry overnight (in a locker). If dry glassware is promptly needed, glassware can be rinsed with acetone and the residual acetone allowed to evaporate. Rinsing with acetone works well because water is miscible with acetone, so much of the water is removed in the rinse waste. Evaporation of small amounts of residual acetone can be expedited by placing the rinsed glassware in a warm oven for a short amount of time or by using suction from a tube connected to the water aspirator. Residual acetone should not be evaporated inside a hot oven (>\(100^\text{o} \text{C}\)) as acetone may polymerize and/or ignite under these conditions. It should also not be evaporated using the house compressed air lines, as this is likely to contaminate the glassware with dirt, oil, and moisture from the air compressor.

    Oven and Flame Drying

    Glassware that appears "dry" actually contains a thin film of water condensation on its surface. When using reagents that react with water (sometimes violently!), this water layer needs to be removed. To evaporate the water film, glassware can be placed in a \(110^\text{o} \text{C}\) oven overnight, or at the least for several hours. The water film can also be manually evaporated using a burner or heat gun, a process called "flame drying". Both methods result in extremely hot glassware that must be handled carefully with tongs or thick gloves.

    Figure 1.11: Flame drying glassware: a) Removal of vinyl sleeves, b) Clamped, c) First moments with a flame, d) After the flame.

    To flame dry glassware, first remove any vinyl sleeves on an extension clamp (Figure 1.11a), as these can melt or catch on fire. Clamp the flask to be dried, including a stir bar if using (Figure 1.11b). Apply the burner or heat gun to the glass, and initially fog will be seen as water vaporizing from one part of the glassware condenses elsewhere (Figure 1.11c). Continue waving the heat source all over the glassware for several minutes until the fog is completely removed and glassware is scorching hot (Figure 1.11d). If the glass is only moderately hot, water will condense from the air before you are able to fully exclude it.

    Safety Note: glassware will be extremely hot after flame drying.

    Regardless of the manner in which glassware is heated (oven or flame drying), allow the glassware to cool in a water-free environment (in a desiccator, under a stream of inert gas, or with a drying tube, Figure 1.12) before obtaining a mass or adding reagents.

    Figure 1.12: Drying hot glassware: a) In a desiccator, b) Under a balloon of inert gas, c) With a drying tube.

    Drying Tubes

    A drying tube is used when moderately but not meticulously dry conditions are desired in an apparatus. If meticulously dry conditions are necessary, glassware should be oven or flame dried, then the air displaced with a dry, inert gas.

    Drying tubes are pieces of glassware that can be filled with a drying agent (often anhydrous \(\ce{CaCl_2}\) or \(\ce{CaSO_4}\) in the pellet form) and connected to an apparatus either through a thermometer adapter (Figures 1.13 b+c) or rubber tubing (Figure 1.13d). Air passing through the tube is removed of water when it comes in contact with the drying agent. Since it is important that air can flow through the drying tube, especially so the apparatus is not a closed system, the drying agent should be fresh as used drying agents can sometimes harden into a plug that restricts air flow. Drying tubes can also be filled with basic solids such as \(\ce{Na_2CO_3}\) to neutralize acidic gases.

    Figure 1.13: a) Drying tube with anhydrous \(\ce{CaCl_2}\), b) Inserting drying tube into a thermometer adapter, Drying tube attached to a: c) round bottomed flask, d) distillation apparatus.


    Lisa Nichols (Butte Community College). Organic Chemistry Laboratory Techniques is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. Complete text is available online.

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