(this section does not print) Teacher’s Notes: Demonstrate the following before allowing the students to get started. 1, How to light the burner. 2, What the different types of flames mean (yellow, blue). 3, The parts of the flame (hottest, pre-combustion, etc). 4, How to pop popcorn kernels on wire gauze supported on a ring stand. About 3: suspend a match in the barrel of the burner using a paperclip or a piece of wire. Do this after letting the burner warm up (once it has been adjusted so it can be re-lighted easily).

Introduction to the Bunsen Burner

Objective

By doing this lab the student will learn how to operate a bunsen burner safely. Also, the student will explore and try to explain an apparent violation of the Law of Conservation of Matter. This is an inquiry lab in which students must design and carry out experiments to complete the objectives.


Bunsen Flame Zones

Overview

The bunsen burner is an extremely convenient source of heat for the chemical laboratory. It was designed by Robert Bunsen more than 100 years ago when he was a researcher at the University of Heidelberg in Germany. He needed a flame that was steady, clean and hot and these are all things that ordinary yellow flames are not. Ordinary flames are sooty and burn at low temperatures. Not to mention how much they flicker. Bunsen’s burner burns blue and very hot because it is designed to completely combust the gas without producing soot. It can do this because it mixes the gaseous fuel with air before it starts to burn.

The burner you will use may have two valves. One of them controls the amount of fuel delivered to the barrel and the other controls the amount of air. If you have a different type of burner then there is only one control built into the barrel. The sliding perforated sleeve controls the amount of air that the fuel mixes with. In this lab you will learn how to operate either type of burner properly.

You will learn how to light and maintain a hot, blue, noisy flame. You will learn the difference between a luminescent flame and one in which soot and light is reduced to a minimum in order to maximize heat. You will learn about the conservation of matter in physical changes such as when popcorn pops.

Bunsen_burner

Materials

  1. bunsen burner
  2. rubber fuel tube
  3. matches/lighter
  4. ring stand
  5. ring
  1. wire gauze
  2. supply of popcorn kernels
  3. metal scoop
  4. lab balance
  5. safety glasses!







Here is the chemical reaction of the bunsen burner fuel with oxygen as it burns:
CH4 + 2O2 —> CO2 + 2H2O
CH4 is called methane and is the major component of natural gas. This equation may remind you of the chemical reaction of the burning of a candle. Notice that carbon dioxide and water are the chemicals that result from the reaction.



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Safety


Procedure

There are three objectives in this lab. You must work in pairs to complete each objective. Before moving on to another section of the lab you are required to obtain your teacher’s initials. Points will be deducted for failing to do so.

While you are working use the data you collect to decide whether you are on the right track. Modify future experiments based on the data you collect. Be reflective and think about what your results mean before proceeding. Do not work to just get it all done as quickly as possible. Finally, be creative! Solving problems in science requires a different kind of creativity from that needed to create art or music but it is just as important in science as in the arts.


Objective One

In this objective you must simply light and correctly adjust the flame of a bunsen burner. All individual students must demonstrate their proficiency in this skill.


Objective Two

In this objective you must establish whether mass is gained, lost, or stays the same when you pop popcorn using the heat of the bunsen burner. You must be able to report how much mass is lost/gained per kernel and what percentage this is of the original mass.


Objective Three

In this objective you must design one or two experiments which could explain why the popcorn gained/lost mass in the experiments you performed in Objective Two. If it is possible to carry out your experiment(s) in the lab, your teacher will advise you on doing so. At no time should you perform experiments not previously authorized by your teacher.

Remember to record your observations in your lab notebook or on a piece of paper in your binder before you leave class. When making observations be sure to use all of your senses except taste. Never taste anything in the chemistry lab. Even if it looks edible.


Objective One

Lighting and Maintaining a Bunsen Burner Flame

gas.outlets.1.open
  1. Connect the fuel tube to the bench fuel valve and to the burner
  2. Completely close the fuel valve (the dial on the bottom) and the air inlet (the barrel)
  3. Light a match or lighter and hold it over the burner’s barrel before turning on the gas
  4. Turn on the lab bench fuel valve as shown in the picture at right; a valve is open if the handle is in line with the outlet—it is closed if it is at right angles to the outlet
  5. Open the built-in fuel valve with 1/2 to a full turn
  6. You should see a bright yellow flame—the light and color are provided by tiny particles of unburned carbon from the fuel which have been heated to incandescence
  7. Turn the air inlet (the barrel) to adjust the flame so that it is a small neat blue cone; you will hear a rushing sound if you have it right
  8. Do not allow too much air to flow into the barrel since this will just blow out the flame; if this happens, turn off the gas and begin again by closing everything down to the way it was when you started
  9. Once you have had your flame approved by your teacher draw the lit burner in your lab notebook; label the parts of the burner and indicate which parts of the flame are hottest
  10. Put the burner out by shutting off the fuel at the lab bench fuel valve; see the picture (the valve on the right is closed); this is the standard procedure for putting out the flame
  11. Make sure that everyone in your group has an opportunity to successfully light the burner; all students should be experienced with this procedure
  12. When all students have practiced lighting the burner, be sure to put it out by turning off the gas

Check-in ______

When you have completed your work in this section check in with your teacher. This is a required part of the lab and your teacher’s initials are required before you can move on to the next objective. Initials will be given for successfully demonstrating that you can light and correctly adjust the bunsen burner.


Summary for Objective One

Answer the questions below before moving on to Objective Two.

  1. Describe the flame of a properly burning bunsen burner.
  2. What does it mean if you have a flame that is tall and bright yellow? How do you correct the problem?
  3. You are trying to light your burner but when you turn on the gas at the lab bench valve the flame of your match immediately goes out. After immediately shutting off the gas what steps must you take to get the burner to light?
  4. Why didn’t the match head suspended over the bunsen burner’s barrel ignite when your teacher lit the burner? What happened when the match was pushed toward the edge of the barrel and why? Explain your answer using evidence and reasoning.

Check-in ______

When you have completed this objective check in with your teacher. This is a required part of the lab and your teacher’s initials are required before you can move on to the next objective.




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Objective Two

Popcorn and the Conservation of Matter

Is mass conserved in the popping of popcorn? Scientists say it is but what do your measurements say? Pop some and find out.

Your teacher will demonstrate a method to use the heat from the burner to pop popcorn. You should practice with a few kernels before popping any as part of your experiments. It may take time to perfect your technique as you may need to adjust the height of the ring or the flame characteristics. Some suggested data to collect:


Design your own data table for this part of the lab. Be sure to plan carefully and leave room for multiple trials of the same experimental set-up, if needed. Also, remember to leave room to enter average values, changes in mass and percent changes. You may find it helpful to use a ruler. Sketch your data table on a separate piece of paper and show it to your teacher for approval before putting the final version here. You must obtain your teacher’s initials before putting your data table here.

Check-in ______




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Summary for Objective Two

Answer the questions below before moving on to Objective Three.

  1. Why do you think that popcorn kernels pop when they are heated? Explain your answer using your own laboratory observations.
  2. How did the average mass of the popcorn before popping compare to the mass of the popcorn after it was popped? Calculate the change in mass and the percent change in mass using these formulas:
    Change in Mass (Δm)
    Δm = Masspopped – Massunpopped
    
    Percent Change in Mass
                 Δm    
     ————————————————————————— × 100%
           Massunpopped
    

    Add these results to your data table, if you have not already done so.
  3. What would it mean if the change in mass is negative?
  4. What would it mean if the change in mass is positive?
  5. Was your change in mass positive or negative? Explain the fact that there was a change in mass and explain why it changed the way that it did.
  6. Does the fact that there was a change in mass show that the law of conservation of matter is false? Why or why not?

Check-in ______

When you have completed this objective check in with your teacher. This is a required part of the lab and your teacher’s initials are required before you can move on to the next objective.





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Objective Three

Popcorn and the Conservation of Matter, continued

In this objective your job is to design an experiment to test your answers to the last two questions from Objective Two. Your experiment(s) must result in data that explain the change in mass of the popcorn kernels. Also, your data must show whether mass is gained from nowhere, gained from an identifiable source, actually destroyed, or is simply difficult to measure. If there is time, and if your experiments are practical, you will be given a chance to carry them out. You need to fill out this section whether or not there is time to attempt the experiments in the lab!


Design your own data table for this part of the lab. Be sure to plan carefully and leave room for multiple trials of the same experimental set-up, if needed. Also, remember to leave room to enter average values, changes in mass and percent changes. You may find it helpful to use a ruler. Sketch your data table on a separate piece of paper and show it to your teacher for approval before putting the final version here. You must obtain your teacher’s initials before putting your data table here.

Check-in ______




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Summary for Objective Three

Answer the questions below using your lab data, if possible. If you could not carry out any experiments for this objective then use your observations from the previous objective to come up with a reasonable answer.

  1. Put the law of conservation of matter in your own words.
  2. Is the law of conservation of matter violated when popcorn is popped? Why or why not? If possible, support your answer with lab data.

Check-in ______

When you have completed this objective check in with your teacher. This is a required part of the lab and your teacher’s initials are required before you can consider this lab finished.


Additional Research

This section is optional but is worth 7 points out of 100 for the whole lab. Turn in your lab as soon as you have your teacher’s initials if you do not intend to do it. If you did everything else well then you can afford not to earn these points. On the other hand, you can use these 7 points to help bring up your overall average…

Research the origins of the establishment of the law of conservation of matter. Look up Antoine-Laurent de Lavoisier (Antoine Lavoisier) and his wife Marie-Anne Pierrette Paulze. The following web sites are a good place to start:

http://en.wikipedia.org/wiki/Antoine_Lavoisier (especially the section on stoichiometry)
http://www.chemheritage.org/classroom/chemach/forerunners/lavoisier.html
http://www.biographybase.com/biography/Lavoisier_Antoine_Laurent.html

The assignment: find at least one other source, preferably a book. Read about Lavoisier. Write two or three paragraphs about his life. Include one paragraph about his work which established the principle of the law of conservation of matter. The point of this research is to understand the origins of the law of conservation of matter. Make it clear in your writing that you understand the law and how Lavoisier gathered evidence for its truth.

Last updated: Feb 22, 2009       Home