01 The Bunsen Burner

USING A BUNSEN BURNER Introduction. Heating is one of the most common procedures in a laboratory and most often we use a Bunsen burner as a heat supply. Other burners in use are improvements of the original invented by a German chemist named Wilhelm Bunsen. For safety reasons many times electric mantles are also used to avoid flames when working with flammable solvents or I case a smoother heating is required. Nevertheless it still plays the leading role in laboratory heating. It is a gas burner and works on a chemical reaction called COMBUSTION. During a combustion process, a fuel (gas) combines with oxygen (air) at high temperature (ignition temperature). As it proceeds, a lot of chemical energy in the gas is released as heat. Three things are needed to keep the combustion process: fuel, oxygen and high temperature. They form what is popularly known as the FIRE TRIANGLE. If one of sides in the triangle is removed the fire will stop.

Below, you can see a labelled diagram showing the different parts of a Bunsen burner. Some Bunsen burners (our burners in particular) lack the flange at the top. Remember the names of the different parts.

Aims In this experiment you will observe and describe some characteristics of the flame of a Bunsen burner.

Materials: A Bunsen burner, some pot, glass tubes, tongs. Procedure 1- Connect the burner to a gas tap. Close the air hole with the collar. Open the gas tap half way to the fully open position. In our lab the gas knob is marked with one white dot for the full open and with two white dots for the half open. Apply a lighted match or lighter to the top of the chimney. 2- Note the appearance of the flame and make a drawing of it. 3- Using tongs, hold a piece of pot in the flame for one minute. Observe the deposit which forms on the cold pot. 4- Slowly open the air hole. Notice the change in the amount of heat and light given out, the length and temperature of the flame and the noise. Draw the flame. 5- With the air hole open repeat (3).with a fresh piece of pot. 6- Hold a piece of soft glass tubing with tongs a- at the top of the flame b- inside the blue cone c- just at the tip of the blue cone. Which is the hottest region of the flame? How can you tell? 7- With the air hole open, turn the gas fully on. Note the appearance and sound of the flame. 8- Fill the following table. Nature of flame Air hole open (gas full open) Colour? Hot or very hot? Noisy? Does it flicker? Does it form soot?

Air hole closed

9- Can you think up an experiment to compare the heating power of both the yellow and the blue flames? (E.g. heating some water). To make it a fair test everything must be kept equal except for the type of flame. When you have planned the experiment ask you teacher to approve your plan before trying it out. 10- Fill in the blanks in the following passage. “To light a Bunsen burner, have the air hole _________ and the gas tap _________ _________. If you leave your burner alight on your bench you want the flame to be clearly seen to avoid ___________: use the _________ flame with the air hole ___________. To heat with the Bunsen burner use _________ flame. Have the air hole _________ and the gas tap __________ __________. For very strong heating, use the roaring flame. Have the air hole __________ _________ and the gas tap __________ ___________.