Bunsen Burner Lab: Tools of the Physical Scientist

Background: Often a chemist needs to heat materials. The Bunsen Burner is oneof the most efficient ways of doing this. Burners come in a variety of designs butmost operate by the combustion of gas with air to produce a hot flame.

A properly adjusted flame consist of two cones; an outer light blue and an innerdark blue cone. The inner cone is the hottest part of the flame because fuelcombustion is most complete here. The outer cone is light blue in color and not ashot as the inner cone. There is also a base cone; a dark cone in the interior ofthe flame. This is where gases mix before they start to burn.

Occasionally you will need to use a yellow flame. This is produced byshutting off most of the air supply. With little air in the fuel mixture, the gasburns incompletely. Unburned carbon in the flame glows to produce theyellow color. This type of flame deposits soot on objects placed in it. bo notuse a yellow flame unless instructed to do so.

Purpose: In this investigation you will learn the parts of the Bunsen burner andtheir functions. You will also learn how to light and adjust a burner flame and tolocate the hottest part of the flame through a series of experiments.

Parts of the Bunsen Burner:A. Barrel - where gas and air are mixedB. Collar - adjust the air intakeC, Air intake openings - air enters hereb. Gas Flow Valve - regulates flow of gas

(can also be controlled from table gas valve)E. Gas intake tube - gas enters burner from

table source.F. Base - supports burner

Materials:striker250 mL beakerevaporating dish

Bunsen Burner100 mL graduated cylindercopper wire

support stand with ringdigital thermometermatch stick

paper clip crucible tongs

Procedures:

Part 1 Examining the Bunsen Burner

1. Unscrew the barrel (or burner tube)the base and locate the parts shownfigure. Think about their functions.

There is a gas inlet (pin hole) at the top ofthe base. Natural gas and air mix in the tube,and this mixture is ignited at the top of thetube.

2. The burner is attached to the house supply of gas by rubber tubing. Inspectthe rubber tubing for cracks or tears; if the tubing is defective, requestnew tubing from your instructor.

The gas flow to the burner inlet is regulated at the gas jet to which theburner is attached. The jet is closed when the handle above it isperpendicular to the jet. It is fully open when the handle is turned so the atis is parallelto the jet. Gas flows throug the attached hose to the burnerbase. The amount of gas entering the burner is regulated by the needlevalve at the base of the burner, If the valve is closed, gas flow is stopped.If the valvue is open, gas will pass through the valve and travel up the burnertube.

The striker is used to light the burner. Check the striker to see if it sparks.If it does not, it may need a new flint which you can get from yourinstructor.

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3. Reassemble the Bunsen burner and connect the tube to the gas outlet. Closethe needle valve and air intake. Put on safety goggles. Make sure that theburner is away from all flammable materials.

Part 2 Lighting the Burner:

1. To light the burner, open the needle valve one to three turns and turn thehandle parallel with the gas nozzle. Bring the striker to the side and justabove the top of the barrel. Hold it at a 450 angle and strike. Repeatstriking, if necessary. If the burner doesn’t light after several strikes, turnthe gas off at the source. The problem may be insufficient gas flow. Repeatthe above steps but this time open the needle valve another turn.(you shouldbe able to hear the gas)

2. Adjust the collar so that the flame is pale blue and a dark blue inner cone isvisible. (see the flame diagram) Your flame should be no more than 3-4 cm.

Parts of the Flame BA Base of flameB Tip of inside blue cone A

Part 3 The Hottest Part of the Flame

1. Hold a piece of copper wire with crucible tongs. Lower the copper wire intothe tip of the outer cone. Record your observations.

2. Slowly lower the wire into the tip of the inner blue cone. Record yourobservations.

3. Last, lower the wire to the base of the barrel. Record your observations.4. Hold an evaporating dish with the crucible tongs and hold it over the flame

for several seconds, up to a minute. Observe what happens to the dish.5. Turn the barrel until the air intake is totally closed off. Observe what

happens to the flame.6. Repeat step four with the air intake closed. Record your observations.

7. Hold the copper wire in the yellow flame. 1ecord your observations.8. Open the air valve back up until you once again have a blue flame. Turn the

Bunsen Burner off.9. Assemble the match stick and paper clip.

Lay the paper clip over top the barrel so thebase of the match stick is inside of the barrel.

10. Light the Bunsen Burner. Allow the match stickto remain in the barrel for about 20-30 seconds.1ecord your observations.

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1. Set up the support stand, ring, and wire screen as shown in the photos.2. Position the ring clamp so that the beaker is at the base of the flame(Position A).

3. Put lOOmL of water into the beaker and record the starting temperature ofthe water on your data sheet.4. Heat the water for 2 minutes recording the temperature every 15 seconds.5. lepeat this procedure for positions B, C, and b using fresh water each time.lecord all data.

Position A(base of flame)

Position B(tip of inner blue flame)

Position C(top of flame)

Position b(2 cm above flame)

Part 4 The Experiment

bata Charts

Copper wire outer cone

Copper wire inner cone

Copper wire air intake closed

Evaporating dish air intake open

Evaporating dish air intake closed

Match stick

Starting 15 sec 30 sec 45 sec 60 sec 75 sec 90 sec 105 sec 120 secTemp

A

BC

b

Analysis and Summary Questions

1. Graph your data for all four positions. Label each line.2. What are the two components necessary for combustion to occur?3. If you completely close the air intake, what color will your flame be?4. What type of flame is the coolest, the luminous (yellow) flame or the non

luminous (blue) flame? How did you determine this?5. What part of the blue flame is the coolest? How did you determine this?6. What part of the blue flame is the hottest? How did you determine this?

How hot do you believe this part of the flame is?(*hint: copper wire)7. What happened to the blue flame when the copper wire was held in the

hottest part? What happened to the copper wire at this time?8. What type of flame do you think is best for heating in the lab? Why?9. Why didn’t the match light when it was placed in the Bunsen Burner?10. What caused the evaporating dish to turn black when heated?