Technique H: Use of a Bunsen Burner
SECTION 1: PURPOSE OF TECHNIQUE
A Bunsen burner is a piece of equipment used for the general purpose of heating substances. When connected to a gas line and lit with either a striker or a match, Bunsen burners generate a controllable open flame that is hot enough for most classroom experimental procedures. The flame produced consists of a visible outer cone and inner cone, in which the topmost tip of the inner cone is the hottest part of the flame (See Figure 1).
In case of emergency, shutting off the gas line is the best way to stop the flame. Make sure the gas line is completely off at all times unless the Bunsen burner is in use.
The Bunsen burners used is a Humboldt model PN 6200.1. These are the standard Bunsen burners used for classroom laboratory experiments but other models and brands exist. Certain attachments are available for Bunsen burners such as fan adaptors (not shown) that can change the shape of the flame if desired.
SECTION 2: EQUIPMENT NEEDED FOR A BUNSEN BURNER
Rubber tubing (gas tubing)
Striker or matches
SECTION 3: SETUP
Part 1: Inspect the equipment
- Check the equipment for broken parts before use.
- Inspect the rubber gas tubing for cracks by stretching it and looking for any major cracks throughout the tubing. If the tubing leaks, discard it and replace with new tubing.
Part 2: Assemble everything together
- Attach one end of the rubber tubing to the arm of the Bunsen burner and the other end to the gas line located on your lab bench.
- Get a striker or some matches.
Part 3: Lighting the Bunsen burner
- Once the Bunsen burner and rubber tubing are secure, turn on the gas line.
- If using a striker, squeeze the handle of the striker over the top of the Bunsen burner to generate a spark where gas is emitted. Do this until a flame appears. Adjust the size of the flame using the gas line knob or the stopcock as needed.
- If using matches, strike the head of the match against the striking strip on the back of the pack. Hold the flame up to the top of the Bunsen burner where gas is emitted until a flame appears. Adjust the size of the flame using the gas line knob or the stopcock as needed.
SECTION 4: IMPORTANT THINGS TO REMEMBER
Precautions and tips for using a Bunsen burner
The gas lines located in the lab benches and the fume hood have a gas pressure of 4 pounds per square inch (psi). For reference, keep in mind that the pressure needed to blow up a balloon is 15 psi (atmospheric pressure). The pressure of the gas lines is not a dangerous amount, but always be aware of its use. When the gas line is on, you will normally hear a slight hissing sound. Natural gas has no smell, but a trace amount of a sulfur compound is added so that it does have odor. You might begin to smell it from unburned gas. To avoid leaks, you should not have the Bunsen burner or the gas line on when not in use.
Bunsen burners are generally safe to use as long as they are used properly and with common sense. For example, the Bunsen burner should be kept away from the edge of the table or anywhere it could easily be knocked over. Do not reach over the Bunsen burner, even if it is off. Be cautious when heating glass containers. If the container is too cold (from either a reaction, ice bath, or other freezing procedure), applying direct heat to the glass may cause it to crack or break.
There are several features on the Bunsen burner meant for controlling the size of the flame, but generally, the most effective way is by controlling gas valve located on your lab bench or in the fume hood. The gas valve controls the amount of gas entering the Bunsen burner. Allowing more gas to enter the Bunsen burner creates a larger flame. Twisting the collar clockwise will reduce the amount of air entering the Bunsen burner, cutting off oxygen supply to the flame. The flame can also be adjusted by using the stopcock located at the bottom of the Bunsen burner, which adjusts the flow of gas entering the Bunsen burner.
Here are some pictures of a Bunsen burner set up:
The hottest part of the flame is located at the tip of the inner blue cone. Bunsen burner flames are hot enough to soften soda-glass, and to fire-polish most other glass types. These flames are not hot enough to melt borosilicate glass, which is used for most other laboratory glassware.
Additional safety tips
Never leave a flame unattended.
Check the area around your Bunsen burner for flammable objects (paper towels, flammable solvents, etc.) prior to lighting the flame.
Hot objects look just like cold objects. Wait sufficient time for objects to cool before handling them.
Metals can conduct heat very well. Be aware that this may happen when heating objects with clamps.
Loose hair and clothing should be tied down to avoid contact with any flame.
Heating glass can create non-visible thermal stress that can weaken glass to mechanical shock, resulting in breakage. Be careful to avoid unnecessary force on areas of glass that have been heated.