A hot plate is a portable tabletop machine that uniformly heats solutions and materials. They are safer than the bunsen burner because they do not consist of open flame but instead consist of the hot plate only.
The maximum temperature range of this device is 350℃, 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. Further, some hot plates are available with stirrers to enhance the automatic mixing of liquids during heating.
Parts of Hot Plate
A hot plate is a simple device consisting of a flat surface with a heating element. It consists of various parts to function that includes;
Controls and indicators
- Power indicator: It illuminates continuously after turning on the switch.
- Heat control knob: It helps to adjust the desired temperature by turning clockwise and counter-clockwise as per requirement.
- Stir control knob: It helps adjust the stir bar’s rotation speed.
- Stirring speed display: It is generally present in a hot plate stirrer that helps to display the stirring speed.
- Heating temperature display: It is in a digital type that helps display the temperature.
- Hot top indicator: It illuminates when the top of the plate is too hot to touch (hotter than 60℃).
- Temperature probe in use indicator: When the external temperature probe attaches to the unit, this indicator illuminates
- External temperature control input: An optional external temperature control input plugs into the connector.
- Power cord input: The power connector of the hot plate attaches to this connector.
- Top plate: The top plate can comprise various materials, i.e., aluminum, ceramic, stainless steel, etc. The central part of the hot plate holds the vessel containing the solutions. It provides the surface to heat the solution uniformly. The type of it that we use depends on the nature of the material to be heated.
Hot plates are available with various accessories to conduct multiple experiments. These include; the vertical support rod, holding rod, external temperature controller, and thermometer holder.
Vertical support rod and holding rod help to provide support to the glassware used in conducting experiments. Similarly, an external temperature controller helps to adjust the temperature and a thermometer helps to hold the thermometer.
Principle of the Hot Plate
The main principle of a hot plate is based on heating through conduction. When you place the sample on a hot plate, heat transfers from the container to the sample through direct contact.
In a hot plate, the temperature control connects to a heating element that encloses inside a plate. When the instrument reaches the desired temperature, the heating element activates, and the plate begins to heat up. The sample is then placed at the top of the plate, transferring heat from the plate to the sample.
Whereas, in the case of a hot plate stirrer, along with a heating element, there is an electromagnet that fits in the internal structure of the hot plate. In this hot plate type, a magnetic bar known as a ‘stir bar’ is placed in a solution containing a beaker that helps to mix the solution by spinning. Two knobs of heat control and rotation control, respectively, fits in a hot plate to control heat and rotation. When the hot plate switch is turned on, a heating knob helps to adjust the temperature. In comparison, the rotation control knob is used to adjust the rotation of the stir bar.
Types of Hot Plate
Hot plates are of various types, but we have to choose based on the material we heat, which are as follows;
Based on Display:
Hot plates are of two types based on display;
- Analog-type hot plates: These are the most simple and cost-effective type. They consist of a knob to adjust temperature and rotation speed. These types of hot plates lack a readout screen to report the exact temperature and speed. However, they consist of an indicator light that helps to know the heating element and operating stirring mechanism.
- Digital type hot plates: This type consists of a temperature and speed control knob and a readout screen. This type of hot plate helps to achieve exact temperature and speed.
Based on Design:
Hot plates are of three types based on the designs;
- Standard hot plates: These types of hot plates are only used to heat the sample. These do not have a stirring function. Further, such types of hot plates require less maintenance and re-calibration routines.
- Magnetic stirrer with hot plates: This type of hot plate consists of a heating system and an electromagnet placed under its surface. The heating system helps to heat the solution, whereas the electromagnet helps to move the electromagnet immersed in a solution to move in a circular motion.
- Stirring hot plates: Heating and stirring elements are installed at the flat top surface in this hotplate type. It is the most expensive type of hot plate that provides uniform heating of high-volume or viscous samples.
Based on materials used:
These instruments are of four types based on the material used to make hot plate surfaces;
- Ceramic hot plates: These plates can endure temperatures up to 350℃ and resist corrosion. These types of hot plates are suitable for glass beakers.
- Polypropylene hot plates: These types of plates cannot withstand high temperatures like ceramic and aluminum plates but has a high tolerance to chemicals, acids, and solvents. These types of hot plates are primarily used in the wet chemistry lab for various purposes.
- Stainless steel hot plates: These plates are highly resistant to corrosion, ether, and alcohol. They are suitable for ISO-grade cGMP spaces.
- Aluminum hot plates: The aluminum plate provides more uniform heat and is tough to crack. It is appropriate for high-throughput lab operations.
Procedure for Operating Hot Plate
The procedure involved in operating hot plates is as follows;
- Place the hot plate on a clean and flat surface.
- Then, switch on the plug connected to the instrument.
- After that, fill the solution on a vessel. Then, place it on top of the intrument (plate where heating occurs), and wait for heating.
- To adjust the temperature, turn the heat control knob clockwise or anticlockwise as per requirement.
- Similarly, in the case of a hot plate stirrer, place the stir bar into the vessel containing the solution and adjust temperature and rotation by turning the temperature control knob and rotation control knob, respectively, into clockwise or anticlockwise directions.
- After the completion of heating, switch off the device.
- Lastly, clean up the device and working area.
Applications of Hot Plate
The hot plate is commonly used in chemistry, zoology, microbiology, physics lab, and also in other areas for the following purposes;
- Laboratory hot plates heat specimens for histological, pathological, and cytological investigations.
- In the microbiology laboratory, hot plates are used to prepare media and reagents.
- In mining industries, hot plates are used to heat hazardous chemicals by using a protective coating.
- These instruments are used to prepare meals in some places where kitchen stoves are unavailable.
- It is used for testing the potency of analgesics by observing the response to heat-produced pain.
- In a chemistry laboratory, hot plates are used to melt solid material, boil liquids, conduct reactions, and also for drying purposes.
Hot plates have a wide range of advantages, which are as follows;
- They are very cost-effective.
- Hot plates are portable devices.
- They are simple to use.
- This laboratory equipment is an essential device in various laboratory procedures.
- They do not require any other source to operate except electricity.
- They are easy to clean and maintain.
Some of the limitations of a hot plate are given below;
- They can produce burns, fires, and electric shocks, resulting in accidents.
- They have a limited temperature range to operate compared to Bunsen burners.
Precautions While Handling
Some precautions that we need to follow while handling hot plates are as follows;
- Always unplug the device when not in use.
- Regularly check the cords and plugs of the device to see if they are damaged or worn out. Similarly, make sure to keep any electrical cord away from the heat.
- Never keep flammable or combustible material near the instrument.
- Always use glassware made up of heat-resistant material, and check its crack before use.
- Make sure to check the thermostat that might have been corrupted by long-term use.
- Do not heat a metal pan or foil on the instrument at 200℃. It can damage the device.
- Use thermal gloves or tongs to remove a hot object from the instrument.
- Hot plate use. UC San Diego. Retrieved on 23rd March 2023. Retrieved from; https://blink.ucsd.edu/safety/fire/requirements/hot-plates.html
- Differences between hot plates and hot plates magnetic stirrer: Pros, cons, and limitations. Retrieved on 22nd March 2023. Retrieved from; https://labproinc.com/blogs/laboratory-equipment/differences-between-hot-plates-and-magnetic-stirrers-pros-and-cons-and-limitations