1.4E: Hotplates

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Hotplates are perhaps the most versatile heat source in the laboratory (Figure 1.48) 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.

Hotplates work by passing electricity through a heating element covered by a ceramic top. Safety note: the hotplate surface can reach temperatures up to \(350^\text{o} \text{C}\),\(^6\) which is hot enough to ignite many low-boiling solvents. Diethyl ether, pentane, hexane, low-boiling petroleum ether, and acetone should therefore never be heated in an open vessel with a hotplate.

Caution should be used when heating any flammable organic liquid in an open vessel on a hotplate, as organic vapors may spill out of containers and ignite upon contact with the heating element, which may be hotter than the ceramic surface. This can be especially true if the hotplate is turned to "high". Therefore, a low setting must be used when cautiously heating certain flammable organic liquids (e.g. ethanol) with a hotplate.

Figure 1.48: Various uses for hot plates: a) Hot filtration, b) Crystallization, c) Benedict's test, d) Visualization or a TLC plate.

\(^6\)As reported in the Fischer Scientific catalog.