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1.4: Heating and Cooling Methods

  • Page ID
    93166
    • 1.4A: Methods and Flammability
      As safety is an important factor in making laboratory choices, it's important to consider the flammability of the liquid to be heated. Almost all organic liquids are considered "flammable," meaning they are capable of catching on fire and sustaining combustion (an important exception is that halogenated solvents tend to be non-flammable). However, this doesn't mean that all organic liquids will immediately ignite if placed near a heat source.
    • 1.4B: Controlled Boiling
      Boiling solutions always have the potential to "bump", where bubbles vigorously erupt from superheated areas of the solution: areas where the temperature is above the boiling point of the solvent, but gas bubbles have not yet formed due to lack of a nucleation site. Bumping can splash hot material out of a flask: onto your hand or onto a hotplate surface where it might start a fire. Bumping is hazardous, not to mention frightening when a bubble unexpectedly erupts.
    • 1.4C: Adjustable Platforms
      Adjustable platforms come in many forms. A lab jack is the easiest to manipulate, and can be adjusted up or down by turning the knob. Unfortunately, lab jacks are expensive so are likely to be used in research settings but not in teaching labs. A simple platform can be made from anything stackable, such as wood blocks or KimWipe boxes, although at some height they can be easily tipped. A more secure platform can be created by placing a wire mesh atop a ring clamp.
    • 1.4D: Bunsen Burners
      Bunsen burners are generally used to rapidly heat high-boiling liquids with low flammability (such as water). Burners do have their place in the organic lab. Burners are often used in steam distillation.
    • 1.4E: Hotplates
      Hotplates are perhaps the most versatile heat source in the laboratory and can be used to heat beakers, Erlenmeyer flasks, and various hot baths (water, sand, and oil baths). They can also be used to develop stained TLC plates.
    • 1.4F: Steam Baths
      A steam bath is a relatively safe way to heat flammable organic liquids. They are designed to heat beakers, Erlenmeyer flasks, and round-bottomed flasks, and have a series of concentric rings that can be removed to adjust to the size of the flask. Many science buildings have in house steam lines in their labs, allowing for this convenient and safe method to heat various solvents.
    • 1.4G: Heating Mantles
      Heating mantles are a relatively safe way to heat flammable organic liquids in a round bottomed flask. The mantles are cup-shaped and designed for different sizes of round bottomed flask. If a mantle does not fit a round bottomed flask perfectly, sand can be added to ensure good thermal contact.
    • 1.4H: Water, Sand, and Oil Baths
      Water, sand, and oil baths are related heat sources as they envelop a flask in a warm material (liquid or sand). A thermometer is often used to monitor the temperature of the bath, and is used to approximate the internal temperature of liquid in a flask (the bath is often slightly hotter than the liquid in the flask).
    • 1.4I: Heat Guns
      Heat guns are inexpensive tools for delivering strong heat in a more flexible manner than other heating methods. Heat can be directed from every direction, and the gun can be manually waved about in order to dissipate the heating intensity.
    • 1.4J: Cooling Baths
      On occasion a solution may need to be cooled: to minimize evaporation of volatile liquids, induce crystallization, or to favor a certain reaction mechanism. Several cold baths are used for certain applications, with the simplest being an ice bath. When preparing an ice bath, it is important to use a mixture of ice and water, as an ice-water slurry has better surface contact with a flask than ice alone.
    • 1.4K: Reflux
      A reflux setup allows for liquid to boil and condense, with the condensed liquid returning to the original flask. A reflux setup is analogous to a distillation, with the main difference being the vertical placement of the condenser. The liquid remains at the boiling point of the solvent (or solution) during active reflux.

    Contributor

    • 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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