Experiment_625_The Bunsen Burner and Glass Working_1_2
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Laboratory Date: Date Report Submitted: |
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Experiment Number and Title |
Experiment 625: The Bunsen Burner and Glass Working
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Experiment 625: The Bunsen Burner and Glass Working
Section 1: Purpose and Summary
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Gain familiarity with how to properly use a Bunsen burner to generate heat and open flames.
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Reinforce safe laboratory practices when using gas and open flames.
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Use the Bunsen burner to work with glass tubing: fire polishing, extruding, and bending.
Fire and the ability to generate heat is an important concept both in everyday life as well as in the laboratory. Without fire and heat, we could not cook food or stay warm in the winter. In the laboratory, fire and heat is oftentimes needed to facilitate a chemical reaction or other type of transformation of matter. To generate heat in the laboratory, we can use a Bunsen burner to produce an open flame. This requires a fuel source (gas, often methane) and oxygen (usually from the air around us). To produce an optimal flame, the Bunsen burner needs to be adjusted to produce an efficient mixture of gas and oxygen.
Bunsen burners used in most laboratories are made of metal that consists of a mixing tube (barrel) attached to the base of the Bunsen burner. You can reference “Technique H: Use of a Bunsen burner” for a detailed description and instructions for use. The base of the Bunsen burner has a gas inlet where rubber tubing is used to connect the Bunsen burner to the gas source on the laboratory bench (Fig.1). On the bottom of the Bunsen burner base, there is a needle valve that screws into the bottom of the Bunsen burner base (Fig.2). Adjusting the needle valve allows more or less gas to enter the Bunsen burner that will mix with oxygen in the barrel. To adjust the amount of oxygen, the barrel can be rotated to allow more or less oxygen through the collar. The collar covers the air inlet holes that allow oxygen to enter the barrel (Fig.3). Once an acceptable mixture of gas and oxygen is flowing through the Bunsen burner, the fire needs to be initiated with a spark or flame. This can be accomplished using a striker or a match to introduce a spark or flame at the top of the Bunsen burner barrel. The initial flame produced by the Bunsen burner may not be optimal so the needle valve and barrel will likely need to be adjusted to achieve a more optimal mixture of gas and oxygen.
Figure 1
Gas inlet and rubber tubing.
Figure 2
Needle Valve.
Figure 3
Complete set up of Bunsen Burner.
An optimal flame receiving the right mixture of gas and oxygen typically has an inner blue cone surrounded by an outer translucent (almost invisible) blue flame (See Fig. 5). Sometimes a third colorless cone will appear inside the inner blue cone that is made up of unburned gas. This optimal flame can be called an oxidizing or nonluminous flame. The hottest part of the flame is the upper tip of the inner blue cone (see image). Different locations within an optimal flame have different temperature and heat outputs. A flame that looks orange or yellow and does not have an inner blue cone is receiving too much gas relative to the amount of oxygen. This may be called a luminous or reducing flame or a cool flame.
Figure 4
Example of sparking flame.
Figure 5
Luminous flame.
As previously described, fire is an important and beneficial resource in life. However, uncontrolled fire and fire that ignites in unintended places can be dangerous. Thus, proper procedures and safety precautions should be used when working with fire and open flames. These include the following (in no particular order of importance):
a) A burning fire/flame should always have a person present to monitor and watch that it doesn’t become uncontrolled.
b) When working closely to an open flame, we need to make sure not to get too close to the flame so nothing catches fire that we do not want to (hair, clothing, other chemicals or lab materials, etc).
c) Care should be taken to make sure that gas is not on when it is not fueling the lit Bunsen burner. If you smell gas, turn off the main gas source on the laboratory bench and wait a few moments before trying to reignite your Bunsen burner.
d) Make sure the gas is turned off when you are finished with your experiment and ready to leave the laboratory.
e) Parts of the Bunsen burner and items you have heated up can get hot even though you can’t see that they’re hot. Use precaution when handling the Bunsen burner that was just turned off and other items that you have recently heated.
f) Always wear lab goggles when working in the laboratory and take special attention to make sure your lab goggles are on when you or someone around you is working with an open flame.
In this experiment, students will work with the Bunsen burner to produce an optimal flame. Then, students will use the flame to do somewhat practical applications.
Section 2: Safety Precautions and Waste Disposal
Safety Precautions:
The materials in this experiment are generally harmless. Use of eye protection is recommended for all experimental procedures.
Tie up or tie back any loose hair. Keep loose fitting clothing away from open flames.
Hot glass looks like cold glass. A good practice is to place the glass you recently heated facing away from you.
Waste Disposal:
Dispose of any unwanted glass in the broken glass container.
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PreLab Questions:
1. What safety precautions should you take while doing the following?
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2. If your Bunsen burner flame is not the right mix of gas and oxygen when you first light it, how do you adjust the Bunsen burner to get to the optimal flame?
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3. What does an optimal flame look like? What is the hottest part of the optimal flame?
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4. Briefly summarize the procedure used to cut the glass tubing before fire polishing it.
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5. What is the purpose of the wing tip that you put on top of the Bunsen burner? What color should the flame be when it is coming out of the wing tip?
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6. You get to bend glass to make a shape of your choice from your imagination at the end of this experiment. What ideas do you have for the shape that you want to make by bending glass tubing?
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Section 3: Procedure
Part 1: Lighting and Adjusting the Bunsen Burner
Reference “Technique H: Use of a Bunsen burner” for a detailed description and instructions for use.
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1. Get a Bunsen burner and a piece of rubber tubing for Bunsen burners. Check for any cracks or damage on the rubber tubing. Get a new piece of tubing if yours is damaged. Attach one end of the tubing to the gas source on the laboratory bench and the other end to the gas inlet on the Bunsen burner. |
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2. Get a match or striker ready. If using a striker, move the movable arm on the striker so that the piece of flint rubs across the rough surface. This will provide a spark that can be used to ignite the Bunsen burner (see image). Use the striker to produce a spark near the top of the barrel of the Bunsen burner. |
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3. Turn on the gas source on the laboratory bench. If it’s a knob, turn it counterclockwise to open and clockwise to close. If it’s a lever style, perpendicular to the outlet valve means closed and parallel means open. Light the match or use the striker to produce a spark and bring it near the top of the barrel of the Bunsen burner. This will light your Bunsen burner. |
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4. Observe the initial flame produced by the Bunsen burner. Record how your initial flame looks below. Is this an optimal flame?
Initial flame observation:
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5. Get a piece of iron wire to test the relative temperature and heat of different parts of your initial flame. Use a test tube clamp or crucible tongs to hold the iron wire. Put the iron wire into various locations in your initial flame and see what happens. Record your observations below.
Iron wire in initial flame observations:
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6. Adjust the needle valve and/or the barrel and collar to change the amount of gas and/or oxygen going into the Bunsen burner. You are trying to achieve an optimal flame that is the result of an efficient mixture of gas and oxygen. |
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7. Hopefully you were able to generate an optimal flame. What does your final flame look like?
Final flame observation:
What did you have to adjust on your Bunsen burner to get your initial flame to your final flame? How easy or difficult was it to produce an optimal flame?
Remarks:
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8. Use the iron wire with test tube clamp or crucible tongs again to test various locations in your final flame and see what happens. What happens to the iron wire when you put it in the hottest part of your final flame? Record your observations below.
Iron wire in final flame observations:
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9. Turn off the gas source at the laboratory bench. This will extinguish your Bunsen burner flame. |
Part 2: Fire Polishing and Extruding Glass Tubing
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1. Get two (2) pieces of approximately 20 cm long glass tubing, a triangular file, and wire gauze. |
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2. You will be breaking a piece of glass tubing in half by scoring it then breaking it (See Fig. 6). Place one piece of glass tubing flat on the lab bench. Hold the triangular file so that your thumb or index finger is on a flat edge of the file and the “cornered” edge of the file is pointing down toward the glass tubing. Use a firm, single stroke of the file to score (make a scratch) on the surface of the glass tubing. You should hear a slight grinding sound as the file is scratching the glass. Look for the scratch mark on the glass. If you need to, score the glass again in the same place until you can see a little scratch. |
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3. Hold the tubing in your hands so the scratch faces away from your body (See Fig. 7). Place each thumb on either side of the scratch mark and break the glass away from you. It may help to wet the scratch mark first with a bit of water. It should not take much pressure from your thumbs if you scored the glass tubing properly. |
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4. Light your Bunsen burner as you learned in Part 1. |
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5. Fire polish the newly broken ends of your glass tubing by place the broken end into the hottest part of your Bunsen burner flame. You will likely see the tip of your glass tubing turn orange when the fire polish is complete. Take your fire polished glass tubing out of the flame and place on the wire gauze to cool. Turn off your Bunsen burner. Record any observations below on what you experienced as you broke and fire polished your glass tubing.
Observations (fire polish):
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6. You will use the other piece of glass tubing to make dropper tips. Light your Bunsen burner. Hold the glass tubing horizontally so the middle of the glass tubing is in the hottest part of the Bunsen burner flame. Rotate the glass tubing between your index finger and thumb so the glass tubing gets evenly heated on all sides. |
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7. When the glass tubing turns gets soft and starts to sag (the flame will turn orange and the glass may start to glow orange), pull the ends of the tubing away from each other at a consistent speed. |
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8. Quickly remove the tubing from the flame and continue to pull the ends of the tubing away from each other. Place the two dropper tips on your wire gauze to cool. Turn off your Bunsen burner. |
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9. When the glass is cool, use the triangular file to cut the dropper tips to your desired size and open up the end of your dropper tips. Record any observations below on what you experienced as you produced the dropper tips.
Observations (dropper tips):
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10. Ask your instructor to observe your fire polished glass tubing and dropper tips and initial below.
Instructor initials:
Fire polish _______________ Dropper tips __________________ |
Figure 6
Scoring glass tube.
Figure 7
Proper finger placement to break the glass.
Figure 8
Endpoint of fire polishing edge.
Figure 9
Heating tubing before pulling to form dropper.
Figure 10
Pulling the glass tube apart to form dropper.
Part 3: Bending Glass Tubing
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1. Get three(3) pieces of glass tubing and a wing tip. |
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2. Make sure your Bunsen burner is cool. Then, place the wing tip on the top of the barrel of your Bunsen burner. The wing tip allows you to spread the Bunsen burner flame so you can heat up a wider surface area of the glass tubing. |
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3. Light your Bunsen burner. The flame should still be blue but now it is spread out instead of looking like a candle flame. You may need to adjust your gas and/or oxygen flow a bit. |
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4. Hold one piece of glass tubing so the middle is in the Bunsen burner flame. Position the tubing so it is almost parallel with the wing tip and flame. This is heating up a larger surface area of your glass tubing. Rotate the glass tubing so the glass tubing gets evenly heated on all sides. |
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5. When the glass begins to sag (the flame will turn orange and the glass may start to glow orange), remove the tubing from the flame and bend it to make a 90 degree angle. Your glass tubing should be smooth throughout the bend and the same diameter as the original glass tubing (not kinked). Place the bent glass tubing on your wire gauze to cool. Record any observations below on what you experienced as you produced the 90 degree bend glass tubing.
Observations (90 degree bend):
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6. Repeat steps 4-5 above with a new piece of glass tubing and make a 135 degree bend glass tubing. Record any observations below on what you experienced as you produced the 135 degree bend glass tubing.
Observations (135 degree bend):
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7. Repeat steps 4-5 above and your experience using the Bunsen burner so far in this lab to make a new shape from your imagination. Ideas may include a corkscrew, a letter in the alphabet, a small square, etc. Make sure that if your new shape requires bending in multiple places, let the area you just heated and bent cool off before you hold that area with your hands to make the next bend. What shape did you make? Draw it out below and record any observations on what you experienced while making the new shape from your imagination.
Drawing and observations (shape from your imagination):
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8. Make sure to turn off your Bunsen burner if you have not already. |
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9. Ask your instructor to observe your bent glass tubing and shape from your imagination and initial below.
Instructor initials:
90 degree bend _______________ 135 degree bend __________________
Shape from imagination:
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10. Disconnect your Bunsen burner from the lab bench gas supply and return the tubing and other equipment. Discard of any unwanted glass from this experiment in the broken glass container. If you choose to take any glass shapes out of lab with you, make sure you store them in a place where they will not break as you transport them. |
Figure 12
Luminous flame
Figure 13
Optimal place to have glass tubing
Figure 14
90 degree bend
Figure 15
135 degree bend
Notes: