Heating in a laboratory

Chemical processes in the laboratory often require application of heat, to treat the chemical, put the chemical reaction in action, determining various flashpoints, melting points and boiling points, and also for drying of glassware for subsequent use. In terms of heating apparatus, heating mantle and hot plate are commonly used across the industry. But which one should you use for your chemical process, and which one suits better than the other? In this article, we try to compare the two, so that you are aware of the pros and cons and can make a better decision.

What is a heating mantle?

A heating mantle is a laboratory equipment which is used to provide heat to lab containers, as an alternative to other forms of heated bath.

When compared to other heating devices, glassware containers can be placed in direct contact with the heating mantle, while also avoiding the risk of glassware shattering. This is due to the fact that the heating element used in heating mantles is insulated from the container, to prevent excessive temperature gradients. They are also commonly referred to as isomantles.

How does a heating mantle work?

A heating mantle assembly can be in below forms:

Electric wires can be cased within a strip of fabric that can be wrapped around a flask. The current supply and resulting temperature is regulated by a rheostat. Such a type of heating mantle is quite useful for maintaining a target temperature, after the contents of a reaction have been removed from a primary heat source.

Another type of heating mantle may resemble a paint can and is constructed as a form of basket within a cylindrical canister. The basket is made of fabric and is supported by a tough metal exterior, and includes heating elements within the body of the heating mantle. To heat the container or apparatus, it is placed within the basket of the heating mantle.

What is a hot plate?

Hot plates are generally used to heat glassware or its contents. Some hot plates also contain a magnetic stirrer, that allows the heated liquid to be stirred automatically.

Hot plates are typically used to avoid the hazards of spillage, overheating or ignition, which are typical in baths since they have high thermal inertia, and mantles can be very expensive and are designed for specific flask volumes.

How does one operate a hot plate?

Here are the common methods of using a hot plate:

One of the methods is by suspending glassware slightly above the surface of the plate with no direct contact. This is helpful in reducing the temperature of the glass, and it also slows down the rate of heat exchange and ensures uniform heating. This works well for processes and chemicals with low boiling point or when the minimum temperature of the heat source is high.

Another method in use, called a teepee setup because it looks a little like a teepee. Here, the glassware is suspended above a plate and the flask is surrounded by a skirt of tinfoil. The skirt should start at the neck of the flask and drape down to the surface of the plate, while avoiding to touch the sides of the flask. This method is used for glassware to be heated at higher temperatures, since the flask is warmed indirectly by the hot air collecting under the skirt and provides better protection from draft air.

Heating Mantle or Hot Plate; which one should you choose?

Heating mantles should be the preferred choice when you are handling organic liquids. When organic liquids are exposed to direct heat, there is the possibility that it could catch fire Heating mantles have enclosed heating systems that serve as a barrier since the heating element is insulated from the vessel containing the sample. This is why heating mantles are preferred over hot plates when heating flammable solutions.

Heating mantles have better safety, energy efficiency and precise control.

 Hot plate should be the preferred choice when heating a large quantity or batch of chemicals. The capacity for heating mantles is usually around a liter, while hotplate stirrers can handle heating up to 20 liters of volume. Hotplates can heat significantly larger volumes than heating mantles.

Hot Plates give the advantage of higher handling higher volumes, easier to procure and offer better stirring capabilities.

Also Read: Magnetic Stirrers: Uses & Types