Laboratory Hot Plate –  Definition, Principle, Parts, Uses

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When working with samples that need to be heated, a hot plate is an indispensable, portable, tabletop machine.

Flat, internally heated surfaces are what hot plates are all about. The device can reach temperatures of up to 350 °C, which is high enough to ignite a wide range of low-boiling solvents such as pentane, hexane, diethyl ether, acetone, and low-boiling petroleum ether. As a result, you should never heat them on hot plates or in an open container.

To ensure that the heated liquid is thoroughly mixed, certain hot plates include a magnetic stirrer. In order to completely dissolve agar, for instance, the medium in which it is to be added must be gradually heated while being agitated at all times.


Students are better off using hot plates instead of hot baths, which pose safety risks due to the potential for overheating, spilling, and ignition, respectively. It’s inefficient since it takes longer to cool, you need to buy expensive mantles, and not all sizes of flasks can use them.

Principle of Hot Plate

  • Typically, a hot plate stirrer operates based on a spinning electromagnetic field. Embedded within the interior framework of the hot plate are a number of electromagnets.
  • A magnetic bar, sometimes known as a stir bar, is put into the solution-containing container.
  • The bar is covered with a non-reactive substance and is hence chemically inert. It must be appropriately submerged in the solution.
  • On top of the heating plate, the beaker or flask containing the solution and stir bar is positioned.
  • The hot plate stirrer has two knobs for managing its operation. One of the knobs is used to modify the device’s temperature, while the other controls the device’s rotational speed.
  • When the hot plate stirrer’s primary switch is engaged, the heating mechanism and electromagnets are triggered.
  • The heating mechanism warms the solution, resulting in the development of an electromagnetic field. This electromagnetic field produced by the device interferes with and interacts with the static magnetic field of the bar magnet, causing the solution to rotate and become thoroughly mixed, so simultaneously causing the solution to mix and heat.
  • The container must be positioned in the middle of the hot plate for proper and uniform stirring. The size of the magnetic bar should be determined based on the solution’s viscosity and volume.

Types of Hot Plates

Based on the design, hot plates are of three types

  1. Standard hot plate: This is a standard hot plate, which is a machine with only a heating system and no stirrer. However, less maintenance and recalibration procedures are required.
  2. Stirring magnet with hot plates: Under the surface of this hot plate is a heating system and an electromagnet. The electromagnet forces the magnetic bar immersed in the solution to rotate at a maximum speed of 2,500 revolutions per minute. Note that the heating plate and magnetic stirrer cannot operate simultaneously.
  3. Stirring hot plate: Here, the heating and stirring elements are positioned beneath the smooth top surface of the machine. It is typically the most expensive variety, but it gives homogeneous heating to samples of high volume or viscosity.

Based on the material used in making a hot plate surface, there are

  1. Ceramic hot plates: These ceramic hot plates can handle temperatures up to 350°C. The tops are corrosion-resistant yet vulnerable to thermal stress from metal cylinders. Use these exclusively to heat glass beakers.
  2. Aluminum hot plates: The aluminium tops offer more heat uniformity than any other heating surface and are more durable and difficult to shatter. The system is appropriate for lab tasks with a high throughput.
  3. Polypropylene hot plates: Warming plates made of polypropylene: Unlike ceramic and aluminium plates, this plate cannot acquire extremely high temperatures. They are, nevertheless, highly resistant to chemicals, acids, and solvents. These plates are utilised in wet chemistry laboratory procedures, including those involving acetonitrile, methanol, and ethanol.
  4. Stainless steel hot plates: These hot plates are very resistant to corrosion, ethers, and the majority of alcohols. They are appropriate for ISO-grade cGMP spaces, clean rooms, and USP-compliant facilities and encourage aseptic conditions.

Parts of Laboratory Hot Plate

Parts of Laboratory Hot Plate
Parts of Laboratory Hot Plate

A. Product Controls and Indicators

  1. Power Indicator: Constantly illuminates when input power is properly connected to the product.
  2. Stir Control Knob: Turn the Stir Control Knob all the way counterclockwise to deactivate the stirring function. Turn it counterclockwise to adjust the stirring speed.
  3. Stirring Speed Display: Displays the speed that has been set for stirring.
  4. Heat Control Knob: Turn the Heat Control Knob all the way counterclockwise to deactivate the heating function. To set the desired temperature, turn the dial clockwise.
  5. Heating Temperature Display: Displays the heating temperature setting.
  6. Hot Top Indicator: Illuminates when the top is too hot to touch (temperature greater than 60°C).
  7. Temperature Probe In Use Indicator: This indicator illuminates when the external temperature probe is attached to the unit.

B. Connections

  1. Input for Power Cord: Connect the provided power cord to this connector.
  2. External Temperature Controller Input: Connect the External Temperature Controller, which is optional, to this port.

C. Top plate

  • A suitable hot plate should be chosen for the materials to be heated.
  • One should be aware of the surface’s thermal conductivity and its maximum temperature tolerance.
  • The top plate may be made of ceramic, metal, or enamel.

To Connect the External Temperature Controller

  1. Turn off both the Stir Control Knob and the Heat Control Knob.
  2. Unplug the power cord.
  3. Insert connector for temperature controller into input connector.
  4. Reconnect the power cable.
  5. The product is now compatible with the External Temperature Controller.
  6. When detaching the temperature controller, repeat the procedure described above.

Operating Procedure of Hot Plate

  1. Ensure the workspace is clean and orderly.
  2. The hot plate should be placed on a level, flat surface.
  3. Ensure the instrument is clean and free of dust.
  4. Connect the power cord to the necessary power source.
  5. Fill the vessel with the solution to be heated and place it on the heating plate.
  6. When the heat control knob is turned clockwise, the heat indicator light will illuminate.
  7. To set the desired heat level, turn the knob on the heat control.
  8. The magnetic stirrer must be inserted into the beaker.
  9. Turn the stir control knob clockwise once the light is on.
  10. Turn the stir control knob to the desired position to adjust the stirring speed.
  11. After completion, turn off the device. Power the supply down.
  12. Clean the equipment and work area.


From a design standpoint, hot plates can vary significantly:

  • Some incorporate magnetic stirrers. This is generally desired for heating liquids, as it aids in heat distribution and removes the need for a separate stirrer.
  • Surfaces of hot plates vary, but often consist of aluminium or ceramic. Choose a hot plate that is suitable with the substances to be heated. Next, examine the surface’s heat transport characteristics and maximum temperature. Choose a different hot plate if you routinely use the maximum heat setting.
  • Some hot plates feature digital readouts and thermocouple inputs, enabling direct control of heat bath temperatures. Some also have safety measures that shut off automatically if the temperature exceeds a predetermined threshold. Don’t select hot plates solely on pricing alone, as these qualities can improve your process and safety.

Current hot plates have heating elements that are hermetically sealed and spark minimally or not at all. However, they are not explosion-proof and should be used under a fume hood while heating organic substances (such as oil baths, or solvents). Typically, the fume hood’s airflow will maintain solvent vapour levels below the flammable threshold. Due to their on/off switch and thermostat designs, older hot plates are more likely to cause a spark hazard. In older types, bimetallic thermostats can fuse shut and send full, continuous current to a hot plate.

Safe Practices with Hot Plates

Hot plates are a safe alternative to procedures involving an open flame, although they are not entirely risk-free. Consider the following safety precautions when using a hot plate:

Safe Practices with Hot Plates


Safe Practices with Hot Plates
  1. On many brands of stirrer/hot plate combinations, the controls for the stirrer and temperature control have identical appearances. Their tasks must be distinguished with caution.
  2. Some hot plate types have been seen to have faulty on/off switches, resulting in continued heating even when the switches are in the off position. This has caused fires in a number of laboratories. Periodically test the “off” switch on hot plates and heating mantles by ensuring the heating equipment cools rapidly. Any unit failing this test must be removed from service immediately.
  3. On some versions, the temperature knobs can be adjusted in the same direction from “LOW” to “OFF” and then to “HI”. In a recent laboratory incident, a researcher rotated beyond the “OFF” position and into the “HI” position, burning the mineral oil bath.
  4. Recognize the location of your fire extinguishers and how to use them. Do not use liquid nitrogen or water to extinguish an oil bath fire, since this could cause burns and cause the fire to spread.
  5. Ensure that the heated glass is composed of heat-resistant materials, such as borosilicates. Soda-lime glass or “soft glass” should not be used on a hot plate since it is not resistant to temperature fluctuations. Do not place glasses with thick walls straight on hot surfaces. It warms unevenly and is susceptible to shattering or cracking.
  6. Before using glassware on a hotplate, check for visible damage and ensure that the hotplate is larger than the object being cooked.
  7. The surface and element of a hotplate can approach the “Flash Point Temperature” of many flammable or combustible substances.
  8. The direct heating of solvents, particularly low-boiling solvents like ether and carbon disulfide (bp 30-60°), poses a fire hazard and should be avoided. Using a water bath will allow for more precise temperature regulation and uniform heat dispersion. If boiling these solvents is required, do not use an open beaker or flask. Use a condenser always.
  9. If the heating system is already hot, the reagent or solvent must be added via a dropping funnel (closed system) rather than a standard funnel. Adding these substances directly will cause a flash fire and moisture absorption.
  10. Remove hot objects from the hot plate using thermal gloves or tongs.
  11. Avoid performing high temperature/pressure reactions unattended.
  12. Water or solvent leakage from the condenser or addition funnels should be avoided, especially when employing an oil bath. Due to thermal shock, the water will likely cause the oil bath container to shatter.

Basic Precautions of Hot Plate

  • Periodically verify that the “off” switch on each hot plate, heating mantle, and water bath works and that the device promptly cools when the switch is in the “off” position.
  • Always inspect equipment before usage. If the plug or cable is worn, frayed, or broken, if the grounding pin has been removed, or if a spark is noticed, do not use the product. Check the thermostat for corrosion, which can also create a spark.
  • Never keep flammable chemicals or combustible materials in close proximity to a hot plate, and restrict the usage of older hot plates for flammable materials.
  • Before using heating equipment, read the manufacturer’s instructions and register the device with the manufacturer so you can be alerted of any recalls or warnings.
  • Unplug any equipment while not in use.

Uses of Hot Plate Stirrer

Laboratory hot plates are devices utilised for heating material in a laboratory setting. Commonly used in chemistry, biology, and other scientific domains to heat substances, solutions, and samples for a variety of applications. Among the typical applications for laboratory hot plates are:

  • Melting solid materials: By applying heat, laboratory hot plates can be used to melt solid substances such as wax and metals.
  • Boiling liquids: Hot plates can be used to bring liquids to a boil, which is useful for a range of applications, including sterilising, concentration, and extraction.
  • Reactions: Many chemical reactions require heat to take place, and hot plates can provide the necessary heat.
  • Drying: By providing heat to evaporate any moisture, hot plates can be utilised to dry substances, such as samples or chemicals.
  • Maintaining temperature: Hot plates can be used to maintain a consistent temperature for items, such as culture media and reagents, that must be kept at a specified temperature.

Hot plates can be used with a number of containers, such as beakers, flasks, and test tubes, and their temperatures can be modified as necessary. They are an essential tool in a variety of laboratory settings and have numerous applications.

Advantages of Hot Plate Stirrer

A laboratory hot plate stirrer is a device that combines a hot plate and a stirring mechanism, permitting the operator to simultaneously heat and stir items. Among the benefits of employing a laboratory hot plate stirrer are:

  • Efficiency: A hot plate stirrer allows the user to simultaneously heat and mix a substance, saving time and effort compared to using a separate hot plate and stirrer.
  • Temperature control: Numerous hot plate stirrers include temperature control functions, letting the user to set and maintain a desired temperature. This is beneficial for chemical reactions requiring precise temperature control.
  • Safety: Hot plate stirrers typically include safety measures, such as overheat protection and automatic shut-off, to prevent accidents and injury.
  • Versatility: Hot plate stirrers can be used with a number of containers, including beakers, flasks, and test tubes, and their stirring rates can be changed as needed. This makes them an adaptable instrument for numerous laboratory applications.
  • Precision: Some hot plate stirrers feature digital displays and controls, enabling the user to precisely regulate and monitor the temperature and stirring speed. This is particularly helpful for investigations requiring exact settings.

Overall, a laboratory hot plate stirrer is an efficient, safe, versatile, and precise device for heating and stirring material in a laboratory setting.

Disadvantages of Hot Plate Stirrer

Although laboratory hot plate stirrers have numerous advantages, they may also have some downsides. Included are:

  • Cost: Hot plate stirrers may be more expensive than separate hot plates and stirrers, particularly if they have modern features such as temperature control and digital displays.
  • Size: Hot plate stirrers can be larger and bulkier than separate hot plates and stirrers, which may be a concern if space is restricted in the laboratory.
  • Complexity: Some hot plate stirrers may contain controls and features that are more sophisticated, making them more difficult to operate for some people.
  • Limited stirring capacity: Some hot plate stirrers may have a restricted stirring capacity, particularly if they are intended for use with small containers, such as test tubes.
  • Limited temperature range: The temperature range of a hot plate stirrer may be restricted in comparison to separate hot plates, particularly if the stirrer is meant for usage with small containers.

Although hot plate stirrers are valuable tools for heating and stirring material in a laboratory, they may not be appropriate for all applications due to their cost, size, complexity, and restricted stirring and temperature capabilities.

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