LAB 1. BURNERS AND FLAMES:
COMBUSTION REACTIONS AND THE SCIENTIFIC METHOD
PURPOSE: To become familiar with the operation of common laboratory burners.
To determine the effect of oxygen on flames.
To practice the scientific method of hypothesis, experimentation, & conclusion.
SAFETY CONCERNS:
Always wear safety goggles.
Tie back long hair when using flames.
BURNERS:
The common laboratory burner is made from a metal tube attached to a base connected to a gas
source. The flow of gas fuel should be started and stopped by opening or closing the gas source
valve on the workbench. The amount of gas entering the burner can be adjusted by turning the
gas inlet valve at the base of the burner. Do not use the gas inlet valve to turn the burner off, as
gas will still be flowing from the main source and cause potential leakage. The amount of air
that enters the burner is controlled by twisting the main burner tube to open or close the air
vents. When turning knobs a general rule is: “righty tighty, lefty loosey”, which means that
turning a knob right will usually turn the flow off and turning a knob to the left will usually turn
the flow on.
COMBUSTION:
The most common fuels we burn to produce heat and light belong to a group of chemical
compounds called hydrocarbons. Hydrocarbons are made from the elements carbon, C, and
hydrogen, H. Wood for our campfires, gasoline for our cars, and candles for our birthday cakes
are all composed of hydrocarbons. When hydrocarbons are combusted (burned) the original
pattern of carbons and hydrogens in the compound is broken and each of the elements, C’s and
H’s, combines with oxygen from the air. Carbons, C, combine with oxygen, O, to form new
compounds called oxides of carbon. Either carbon monoxide, CO, or carbon dioxide, CO2, are
formed depending on the number of oxygens, O’s, available. Hydrogens, H’s, combine with
oxygen, O, to form the familiar oxide of hydrogen, H2O, called water.
When there is an abundance of oxygen present in the burning of a hydrocarbon, then there is
enough oxygen, O, to allow each atom of carbon, C, to join with two oxygens, O, to make carbon
dioxide, CO2, a colorless, odorless, gas. This is called “complete combustion” of a
hydrocarbon fuel because each carbon atom has been completely oxidized. Each carbon has
bonded with the maximum number of oxygens possible.
Without enough oxygen present some carbons, C’s, may find only one oxygen, O, with which to
combine to form the colorless, odorless gas carbon monoxide, CO. Other carbons, C’s, may not
find any oxygen at all and be left as elemental black carbon soot, C. Elemental carbon soot, C,
and carbon monoxide, CO, are the results of having incomplete oxidation of the hydrocarbon
fuel. Burning a hydrocarbon without enough oxygen to completely oxidize each carbon is called
“incomplete combustion”.
CH110 Lab 1. Burners & Flames
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When a laboratory burner is burning hydrocarbon fuel with plenty of oxygen in the process of
complete combustion it makes a loud roaring noise and appears as a clean blue flame with a cone
in the middle. This is called a “hot flame”.
When a laboratory burner is burning hydrocarbon fuel with insufficient oxygen in the process of
incomplete combustion it is very quiet and appears as a billowy yellow flame. This is called a
“cold flame”.
Hot air balloons are equipped with two kinds of burners to provide the hot air needed to lift the
balloon off the ground. The preferred burner burns very cleanly so as not to fill the balloon with
soot, but it is also quite noisy. The other burner is nick named the “cow burner” gets used when
flying over animals that may be startled by noise. It is very quiet but produces more soot.
CHEMICAL EQUATIONS:
A way to describe the change of one chemical compound into another is by using a chemical
equation. A chemical equation shows the number and formulas of all compounds that react
together (reactants) on the left side of a reaction arrow, and the number and formulas of all
compounds produced (products) on the right.
The chemical equation to describe the complete combustion of a common hydrocarbon fuel,
propane (C3H8), is as follows:
C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g)
This chemical equation for the complete combustion of propane can be translated into words. It
means “one molecule of propane gas, C3H8(g), will react with five molecules of oxygen gas,
O2(g), to produce three molecules of carbon dioxide gas, CO2(g), and four molecules of water
vapor, H2O(g).
Oxygen, in a chemical equation, is written O2 instead of just O because, like socks, they always
start out in pairs. The elements that occur in pairs when they are alone are called diatomic
molecules. The elements that occur as diatomic molecules are H, O, F, Br, I, N, and Cl.
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CH110 Lab 1. Burners & Flames
SCIENTIFIC METHOD:
As we observe the world and how it works, questions arise to which we would like answers or
explanations. For example we have just discussed combustion and learned that completely
burning a hydrocarbon results in the production of carbon dioxide, CO2, and water, H2O. We
may now ask.
QUESTION: “Will a burning candle give off water?”
The first step in answering a question is proposing a hypothesis. A hypothesis is an educated
guess to give and explanation, or answer a question, based on experiments you, or someone else,
have already done. In regards to our question about a burning candle giving off water, we can
state a hypothesis based on what we’ve learned in our prelab discussion, which was the result of
someone else’s experimentation long before us.
HYPOTHESIS:
I think that a burning candle will give off water vapors. I believe this because
candle wax is made of hydrocarbons and I learned previously that when any
hydrocarbon is burned it gives off both carbon dioxide and water.
To answer a question with more confidence than just an educated guess, tests or experiments
must be designed and performed to justify the answer. By experimentation we gather firm
evidence or results that we can use to either prove or disprove the hypothesis.
EXPERIMENT:
1. Light a wax candle. (Either a paraffin or a beeswax candle will do, since both
are made of hydrocarbon.)
2. Bring a glass beaker or a watch glass close to the flame and watch to see if any
water vapors condense on the glass.
3. If any water vapor is visible on the glass it must have come from the burning of
the hydrocarbon candle wax.
RESULTS:
When I brought the glass close to the burning candle I saw some water
condensation appear. When the glass got hotter in the flame the water
condensation disappeared.
Experiments must provide enough evidence to eventually allow reasonable conclusions about
whether or not the initial hypothesis was correct. Often multiple experiments must be performed
to be certain that the results are repeatable. Sometimes the hypothesis must be revised and then
tested repeatedly until confident conclusions can be made.
CONCLUSION:
Water is produced from the burning of a candle. I know this because I was able to
see condensed water vapors that were produced from the burning of the candle.
My original hypothesis was correct. Water does indeed result from the combustion
of a hydrocarbon candle.
CH110 Lab 1. Burners & Flames
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When designing any experiment the potential for errors must be taken into account. Errors
occur whenever any kind of measurement is made as well as when sloppy technique is used. It is
impossible to avoid all errors. Each error must be recognized and considered whenever
conclusions are made.
ERROR ANALYSIS:
The water that condensed on the glass vaporized and then was no longer visible if
the flame was allowed to heat up the glass. For our experiment to show water as a
product the vapors must be condensed on a cool glass.
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CH110 Lab 1. Burners & Flames
PROCEDURES:
NOTES:
ACTIONS:
1
I. LABORATORY BURNER:
1. Complete the drawing of the laboratory burner
provided on the report sheet (Box I) by drawing in
and labeling the following:
A. Gas source valve
B. Gas inlet valve
C. Air inlet
II. COLD FLAME:
2. Light your burner1 by turning on the gas2 at the
source and quickly igniting the gas and air mixture at
the top of the burner tube using a match or striker.
You may have to adjust the gas inlet
valve to allow enough steady gas
flow to keep the burner going without
blowing out the flame.
2
The fuel we are burning is a
hydrocarbon gas made from the
elements carbon, (C), and hydrogen,
(H). When hydrocarbons are burned
or combusted the carbons, C,
combine with oxygen, O, to form
carbon monoxide, CO, or carbon
dioxide, CO2 and the hydrogen, H,
combines with oxygen, O, to form
water, H2O.
3
3. With the burner lit, close off the air supply by turning
the metal air inlet tube to the right (screw it down).
On the report sheet (Box IIA) draw a picture and
describe with words the appearance and sound of
this flame formed when there is a limited supply of
oxygen.3
4. With tongs, hold a clean, dry porcelain evaporating
dish in the middle of the oxygen deficient flame. In
the space provided on the report sheet (Box IIB),
describe and draw a picture of the resulting dish.4
III. HOT FLAME:
5. Open the air inlet of the lit laboratory burner by
turning the metal air inlet tube to the left (unscrew it)
to increase the amount of oxygen supplied. Allow
enough oxygen to enter the tube to make a blue cone
about 5-6 cm (2 in) high. On the report sheet (Box
IIIA) draw a picture and describe with words the
appearance and sound of this flame formed when
there is an abundant supply of oxygen.5
6. With tongs, hold a clean, dry, porcelain evaporating
dish above the tip of the blue cone of the oxygen
abundant flame. In the space provided on the report
sheet (Box IIIB), describe and draw a picture of the
resulting dish.6
7. Hold an index card on the metal burner tube in your
hot flame just until the paper begins to burn. Quickly
quench the burning card with a stream of running
water. Draw a picture of the burnt card on the report
sheet (Box IIIC). 7
CH110 Lab 1. Burners & Flames
You now have a flame that has very
little added oxygen. It would be
similar to the flame of a candle that is
not equipped with an additional air
inlet source. This is called a “cold”
flame.
The black soot you’ve collected on
the porcelain dish is the element
carbon, (C). It occurs when there is
not enough oxygen present to
combine with all of the carbons in the
fuel so some free carbons get left
alone. Some of the carbons that do
get oxygen get only enough to form
carbon monoxide, CO.
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5
You now have a flame that has a lot
of added oxygen. This is called a
“hot” flame.
6
There is less of the black sooty
carbon formed because there are
enough oxygens available to combine
with all of the carbons to make
gaseous carbon dioxide, CO2. Fewer
C’s get left over alone as C, and
fewer C’s get turned into carbon
monoxide, CO.
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It appears that not all parts of the
“hot” flame are equally hot. Since
the hottest part of a flame is just
above the inner blue cone, that is the
best spot to place a substance you
intend to heat.
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IV. SCIENTIFIC METHOD:
As you follow the instructions given in this section you will answer the given question by
practicing the scientific method. Use the example given in the discussion section at the
beginning of this lab chapter to help you. The question we’ll tackle is:
Will an unlit match catch on fire if it is suspended inside the blue cone of a
laboratory burner?
1. Make an educated guess, or hypothesis, to answer
the question. Explain why you came up with the
hypothesis you did based on what you have learned so
far from your work with burners and flames.
2. Create an experiment that would test your
hypothesis.8 Write out detailed step by step
procedures that you or someone else could follow.
Include some instructions for your reader as to what
to observe.
3. Perform the experiment you designed and describe
the results on the report sheet. If you need to repeat
the experiment to get repeatable and conclusive
results do so. When you are satisfied with your
experiment have your instructor observe the results
and initial your report sheet.
4. Now make a conclusion statement that sums up the
answer to the original question. This time give
factual evidence from your experiment to support
your answer. 10
5. Write down any warnings, analyze any potential for
errors, or any cautions for the performing of your
experiment to achieve reliable results.11 Is there
anything you might have done differently if you had
the chance to do your experiment over?
6. What other unanswered question might you write
that may have arisen from your work or study of
burners, flames, and combustion that might lead to
other future experiments? 12
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CH110 Lab 1. Burners & Flames
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Hint: Figure out how you could
suspend the match in the metal tube
before the burner is lit. Straight pins
are available. There may be more
than one way to do this. You could
be creative.
9
Your procedures must be detailed
enough so that anyone can follow
them. Don’t assume your reader
already knows what to do.
10
This time your answer can be more
than an educated guess. It can be a
confident conclusion based on an
actual experiment rather than just a
hypothesis.
11
With any experiment it is important
to question the methods and revise
them if needed. Often it takes many
revisions of an experiment to make
sure that it is an accurate and efficient
way to arrive at a true conclusion.
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When we look at things and how
they work we often come away with
more questions to answer. If we ask
good questions and design new
experiments to answer them we learn
more truths. This is how many new
scientific discoveries have been
made.
LAB 1. BURNERS AND FLAMES:
PRE LAB EXERCISES:
NAME_____________
DATE______________
1.__
A Hydrocarbon can best be described as
A a compound made from carbon and water.
B. a compound made of primarily carbon and hydrogen.
C. a water soluble carbon compound.
2.__
At what place should we shut off the laboratory burner?
A. The gas source
B. The gas inlet valve
C. The air inlet valve
D. All of these are fine.
3.__
Incomplete combustion is most likely to result from
A. running a car engine in a closed garage.
B. cooking on a barbeque grill indoors with the windows and doors closed.
C. cooking on a propane grill outside.
D. Both A and B.
E. All of these.
4.__
Automobile carburetors allow air to mix with the gasoline fuel that provides energy for
the car to move. A carburetor needs to be adjusted to maintain the proper oxygen to fuel
ratio. If the oxygen to fuel ratio is high (meaning lots of O’s compared to C’s) the result
is
A. only a little CO2, lots of CO, and lots of C.
B. lots of CO2, lots of CO, and only a little C.
C. lots of CO2, only a little CO, and only a little C.
D. only a little CO2, only a little CO, and lots of C.
5.__
A hypothesis is
A. the scientific answer to a question.
B. an educated guess.
C. an experiment to perform.
CH110 Lab 1. Burners & Flames
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CH110 Lab 1. Burners & Flames
LAB 1. BURNERS AND FLAMES:
NAME___________________
PARTNER_________DATE___
REPORT:
I. LABORATORY BURNER
I.
III. HOT FLAME
IIIA.
Drawing
Appearance
Colors
Sound
IIIB.
II. COLD FLAME
IIA.
Drawing
Appearance
Colors
Sound
IIB.
IIIC.
CH110 Lab 1. Burners & Flames
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IV. SCIENTIFIC METHOD:
QUESTION:
Will an unlit match catch on fire if it is suspended inside the blue cone
of a laboratory burner?
A. HYPOTHESIS: (To be done before any experiment is done.
Use complete sentences; give rationale for
your hypothesis based on previous information. Why do you believe what you believe?)
I believe that unlit match suspended inside the blue cone of a lab burner will _______
________________________________. I believe this because ________________
____________________________________________________________________......
B. EXPERIMENTAL PROCEDURE: (Give details that others could follow; include instructions
for what to look for and how to determine if your experiment is accomplishing your goal.)
C. RESULTS: (Report findings or data from experiment.)
Instructor’s Initials ____
D. CONCLUSION: (Restate hypothesis based on new knowledge from your experiment.)
E. ERROR ANALYSIS: (Give warnings or advice for modifications to others performing your
experiment. Give potential for errors.)
F. FURTHER QUESTION(S): (What new questions might this experiment inspire?)
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CH110 Lab 1. Burners & Flames
LAB 1. BURNERS AND FLAMES:
NAME________
POST LAB EXERCISES:
1.___ The center of the blue cone of a hot flame
A. is the best area to put an item you wish to heat.
B. is the hottest part of the flame.
C. contains no fire at all.
2.___ To give the highest heat to an object where should it be placed?
A. In the center of the blue cone of a hot flame.
B. In the center of a cold flame.
C. 5-6 cm above the cone of a hot flame.
D. At the tip of the blue cone of a hot flame.
3.___ The “cow burner” on a hot air balloon described on page 2 is an example of
A. incomplete combustion
B. complete combustion
4.___ Driving down the highway you see black soot coming out of the exhaust. The identity
(chemical composition) of the soot is
A. carbon monoxide
B. carbon dioxide
C. elemental carbon
D. dirt
5.___ Driving down the highway you see black soot coming out of the exhaust. How was the
black soot produced?
A. hot oil and dirt are blown out.
B. lack of oxygen causes incomplete combustion of the hydrocarbon fuel where carbons
don’t have enough oxygen to convert each C to CO2.
C. excess oxygen causes complete combustion of the hydrocarbon fuel where carbons
have enough oxygen to convert each C to CO2.
6.___ Driving down the highway you see black soot coming out of the exhaust. What
specifically should be done to avoid it?
A. Clean the soot deposits out of the engine.
B. Open the hood and stand and look at the engine.
C. Adjust the carburetor so that less oxygen is mixed with the fuel.
D. Adjust the carburetor so that more oxygen is mixed with the fuel.
7.
Translate the following word description into a chemical equation for the incomplete
combustion reaction of propane. (Hint: Model after the word translation of the complete combustion
example in the discussion section at the beginning of this lab chapter.)
Two molecules of propane react with seven molecules of oxygen (O2 remember) to form
six molecules of carbon monoxide and eight molecules of water.
CH110 Lab 1. Burners & Flames
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CH110 Lab 1. Burners & Flames