Using a Bunsen Burner

Pre-Lab Questions Put your responses on your green answer sheet. Answers will be found below as you read.

1. What is the purpose of this lab? 2. Define combustion. 3. What is a hydrocarbon? 4. What 3 things are needed to for combustion to occur? 5. What is the chemical name and formula for natural gas? 6. What 2 substances are produced during the complete combustion of a hydrocarbon? 7. What element is necessary to ensure complete combustion? 8. When is soot produced? 9. What element is responsible for soot? 10. Why do chemists prefer to use blue flames?

I. Purpose: The purpose of this lab is specifically to learn how to:  start a Bunsen burner,  adjust its flame,  safely use the burner, and  determine the relative “hotness” within the different areas of the flame.

II. Introduction:

A. Background on Combustion.

1. Combustion is the rapid burning of a hydrocarbon (a substance containing hydrogen and carbon) that releases energy in the forms of heat and light. For combustion to occur, you need a source of fuel, oxygen, and a spark. The fuel we use is natural gas, a hydrocarbon whose chemical name is “methane”, and chemical formula is CH4 . Oxygen gas is naturally present in the air around us. 2. During combustion a hydrocarbon chemically combines with oxygen to produce mainly carbon dioxide gas and water vapor. When plenty of oxygen is available, combustion will be “complete”; and only carbon dioxide and water vapor will be produced. Complete combustion results in a blue flame, and no soot is formed. The temperature of a blue flame is hotter than that of a yellow flame. 3. When insufficient (not enough) oxygen is present, combustion in said to be “incomplete”, and unburned bits of the element carbon (from the original fuel), now called “soot”, will remain. Incomplete combustion gives us a relatively cool “luminous” yellow colored flame. An example of a luminous flame is candlelight. Candles don’t burn hot enough to give us blue-colored flames. 4. Chemists prefer nonluminous blue flames because of their cleanliness and their high heat.

B. Background on the Bunsen burner.

1. A Bunsen burner is a heating device commonly used in laboratories because it can provide a hot, steady, smokeless flame. It is named after the German chemist who popularized its use. 2. The burner is a short vertical tube of metal connected to a gas source and perforated at the bottom to admit air. An adjustable collar on the barrel (chimney) controls the upwards flow of air. 3. Natural gas fuels can produce flame temperatures up to ~1900oC (3500oF). Use caution! 4. A Bunsen burner can be set up to provide a flame having two visible, distinctly blue-colored, areas (cones), called the “inner blue cone” and “outer blue cone”. Surrounding these is an invisible third cone. These hot blue cones are caused by the focused air coming up through the barrel. Before We Start: Safety Concerns—

A flame should only ever be seen above the barrel: - If your flame squirts out sideways, from the base of the burner, turn it off. Then tell your teacher. -If a fire develops WITHIN the barrel, turn it off. Then tell teacher. If the barrel comes off, turn it off. Then tell teacher. If the gas valve comes off, turn it off. Then tell teacher. If hose breaks turn it off, tell tch

--So, if you need to turn off the burner quickly, safely, and correctly, this is how: The handle of the “jet” (the pointy handle coming out of the bench) should be pushed all the way back so that it lies as far to one side or the other as possible. Either direction is OK. Don’t leave it in the middle.

III. Procedure:

A. Gather supplies: 1 Bunsen burner with tubing 1 large tongs 1 striker 1 evaporating dish 1 length of copper wire

B. Sketches:

1 1. Connect Bunsen burner tubing to the gas jet which protrudes from the lab bench. 2 2. Sketch your burner set up. 3 3. Label sketch: “gas jet” (gas source), “gas inlet valve”, “barrel” (chimney), “air inlet” (windows) 4. Sketch your striker. Label: “flint” and “file”.

C. Using the Bunsen burner: --

**Until you are an “old pro”, start it with a low amount of methane and no air flowing at all. The following directions will help you set it up this way.

1. Steps to use to start your burner:

a. Close the air inlet (windows) by rotating the barrel downward all the way. b. Close the gas inlet valve (at the burner base); then open it minimally by loosening it. 4 c. Fully open the gas jet, which is on your lab benchtop, so that the pointy handle points straight out (“in the middle”, pointing toward the tubing). 5 d. Hold your striker so that it is just above the Bunsen burner’s barrel, and push the flint along / across / into the file so that the friction creates sparks. Keep trying. Push hard! --If the flame doesn’t light, increase the gas flow to a full 1 turn open. Let your partner have a go.

2. Steps to use to observe soot. [If you tried this using a blue flame, you would NOT see any soot.]

a. While the flame is yellow, turn the gas inlet valve (on the burner base) until the flame is pretty high. b. Use large tongs as your teacher has described, to hold the dish in your flame until you see soot, a black powdery deposit. The dish is now VERY HOT AND DIRTY. Set it somewhere on the bench. c. Allow your dish it to cool before washing it – tap water and a towel. Dry before leaving.

*Lab Questions. [Put answers on your green answer sheet in box marked “lab questions Q1-3”

*Q1. What part of the Bunsen burner lets you change the height of a flame (gas inlet valve or barrel)? *Q2. What color is the flame when the fuel is not pre-mixed with air (when the barrel is all the way down)? *Q3. What part of the Bunsen burner allows you to control the amount of air (gas inlet valve or barrel)? Continue Onwards…… 3. How to adjust the flame so as to have blue inner and outer cones:

Turn the barrel upwards so that you allow more air to enter. As you keep turning the barrel, you will see the yellow flame turn into first a solid blue cone, then into 2 separate blue cones. Stop when (or if) you hear a “blowing” noise and see your flame flicker dramatically. This would mean that you currently have the maximum amount of air you can have without blowing out your flame. If you open the air inlet too much more, the flame blows out. Oops. If your flame just burned out, relight your burner. I suggest turning down the amount of gas (gas valve bottom of burner) as well as turning down the air flow (lower the barrel).

4. How to observe the “invisible third cone”:

Spark your striker somewhere above the two blue cones. You will see “sparkles” wherever the third cone is present. Pretty!

5. Determining relative hotness within your flame:

A. Adjust the flame so that you have 2 visible nonluminous (blue) cones, and the flame is a good working height. B. Follow the procedure which your teacher will demonstrate in order to test for relative temperatures. --The coolest part of the flame will leave the wire “unaffected”, --Hotter areas will “scorch” (or blacken the wire), --At still hotter areas, the wire becomes “red hot”, --and at the hottest places the wire will melt. For each of the 5 areas which you test, you should write one of these words: “unaffected”, “scorches”, “reddened”, or “melted”. Record this qualitative data on your answer sheet.

Area #1 – touching the barrel. Area #2 – middle of the inner blue cone. Area #3 – very top of the inner blue cone. Area #4 – very top of the outer blue cone. Area #5 – middle of the invisible cone (way above the outer blue cone).

6. How to turn off the Bunsen burner the safe way, the correct way, the ONLY leak-proof way:

Use the “jet” – the pointy handle coming out of the lab bench. Push the handle all the way back so that it lies as far as possible to either side. Push it either to the left or to the right. It will now lie at a right angle to the attached tubing.

Clean Up – Leaving Bench, Cupboard, Drawer, etc as you found it today. Return to classroom, work on Post-Lab questions (below) till finished. Responses go on green answer sheet.

11. What are the names of the two easily visible areas within a Bunsen burner’s flame? 12. Are these two areas present (to an appreciable extent) within a candle’s flame? 13. What should you do if you develop a fire within the barrel, or at the base of your burner? 14. To light a Bunsen burner when you are a beginner, should the air supply be mostly opened or closed? 15. What does it mean if you hear a “blowing” noise while using your Bunsen burner? 16. What is the correct way to turn off a Bunsen burner? 17. Did you make mostly qualitative (non-numeric) or quantitative (numeric) observations in this lab? 18. Rank these observations in order from “least hot” to “most hot”: melting, scorching, reddening.