Laboratory Safety: Using Heating Devices

Why heating is part of practical chemistry

Heating can help a substance dissolve, speed up a reaction or bring about a change that can be observed. The important skill is not simply making something hot: it is choosing a suitable heating method and controlling it safely. In OCR Chemistry A practical work, this includes using a Bunsen burner and a water bath or electric heater. The method depends on what is being heated and how gently it needs to be warmed.

Heating with a Bunsen burner

A Bunsen burner supplies heat from a gas flame. Put it on a heatproof mat. To heat a beaker or flask, support the vessel on gauze and a tripod above the burner so that it stands securely rather than being held in the flame. Light the burner with its air hole closed to give a visible yellow safety flame; open the air hole for the blue heating flame. Adjust the heating so the liquid warms or boils gently, rather than boiling so vigorously that it spits or overflows.

Wear eye protection and stand while heating. Keep loose clothing and hair away from the flame. Hot glass can look just like cold glass, so use a test-tube holder or other suitable handling equipment, place hot apparatus somewhere safe to cool, and do not touch it until it has cooled. Turn off the gas when heating is finished. Scalding liquid and steam are hazards as well as the flame itself.

Indirect heating with a water bath

A water bath warms a sample through surrounding water instead of exposing its container directly to the flame. For a simple school setup, put water in a beaker on a tripod and gauze above a Bunsen burner, then stand the sample’s test tube in the water. Heat the water carefully and observe the sample as it warms. This gives gentler heating than placing the test tube directly in a flame. In one Royal Society of Chemistry activity, test tubes containing chocolate and egg white are warmed in this way, then transferred with a holder to a rack to cool.

An appropriate electric heater is another heating option named by OCR. It avoids a naked flame, but its surface and the heated vessel can still cause burns. Use the equipment provided and follow the instructions and safety procedures for that particular heater. Whichever method is chosen, keep the apparatus stable, heat only as strongly as needed, and allow hot equipment to cool before handling it.

Choose and control the heat

A Bunsen burner provides direct flame heating. Use a heatproof mat; support a beaker or flask on a tripod and gauze. Light with the air hole closed (yellow safety flame), then open it for the blue heating flame. Heat gently and turn off the gas afterwards.

A water bath warms a sample indirectly through heated water. An electric heater is another suitable heating device; follow its operating instructions and remember that it remains a burn hazard.

Work safely

Wear eye protection, keep clear of flames and hot surfaces, and use a holder or suitable equipment for hot glassware. Leave hot apparatus in a safe place to cool.