A Scientific Inquiry Into The Burning Of A Candle
A Scientific Inquiry into the Burning of a Candle
Mastery Objectives and Critical Skills for this Laboratory Investigation
· Make and accurately record a combination of at least 10 precise qualitative and quantitative observations of a burning candle
· Create a meaningfully organized table of observations
· Develop the ability to ask precise, testable questions
· Accurately record lab procedures
· Practice the correct formatting and use of a laboratory notebook
· Make informed predictions based on laboratory data
· Be able to explain how specific chemical concepts are related to the events surrounding a burning candle
Before You Start –
The scientific process is a systematic way of explaining how events are related to each other in the natural world. Careful observations are the first step in this process. An observation is a fact obtained with the senses.
You might think that a burning candle is pretty simple. But, if you really look at it, a burning candle turns out to be a rather complex process.
During this lab investigation, you will observe a burning candle, formulate questions about the process, and conduct experiments to gain insight into what is happening. What you find may surprise you!
Background on Candles to Help You Get Thinking
A candle is made of paraffin (also known as paraffin wax (C25H52)), and a wick of cotton (C6H10O5). Paraffin is purified from crude oil, and is thus a petroleum product. Petroleum is formed in the Earth in a natural process over the period of millions of years. Paraffin is a mixture of molecules made of carbon and hydrogen. The hydrogen and carbon composition of paraffin is the reason it is classified as a hydrocarbon. Although paraffin is comprised of a variety of different molecules, a typical molecule contains 25 carbon atoms, and 52 hydrogen atoms; we can use this to give us C 25 H 52 as a rough chemical formula for paraffin. Paraffin, like other products from crude oil such as gasoline, diesel, and kerosene, is a hydrocarbon fuel. The burning of any hydrocarbon produces carbon dioxide (CO 2 ) , water (H 2 O) , and heat.
The wick in a candle is typically a braided cotton string. Cotton consists largely of cellulose. Cellulose is the most abundant biomolecule on Earth. It is composed of six carbon (C), ten hydrogen (H), and five oxygen (O) atoms.
Materials
· candle
· fingerbowl
· matches
· aluminum foil
· 250mL and/or500mL Erlenmeyer flask
· timer
· metric ruler
· balance
I. Observing an Unlit and a Lit Candle
Procedure
1. Light the candle, drip enough wax onto the center bottom of the fingerbowl to attach the candle.
2. Observe the candle accurately and precisely. Use your senses: sight, sound, feel, smell (but not taste!). Record at least 10 precise observations in your lab notebook under the heading "OBSERVATIONS, BEFORE BURNING."
3. Light the candle. Observe the candle and flame as carefully as you can. Record at least 25 observations in your lab notebook under the heading "OBSERVATIONS, DURING BURNING." Include a fully labeled color sketch with a scale for sizing. (Observe the candle burning for at least five (5) minutes.)
4. Blow the candle out. Observe the candle until no more changes are taking place. Record at least 10 precise and accurate observations under the heading "OBSERVATIONS, AFTER EXTINGUISHING."
Observations are almost always followed by questions. Write six questions that arose from your observations under the heading “FURTHER QUESTIONS” following your observations.. Only write questions for which you do not know the answer! If formulating six questions is difficult, you may not have observed the candle carefully enough. Relight, and observe again!
II. Six (6) Experiments with a Candle that Generate Questions
D o the following f or each of the experiments below :
1. Read the experiment.
2. Predict what will happen when you do the experiment. Record your
predication(s)
3. Perform the experiment
4. Record your observations.
5. Record which predictions panned out and which didn’t and offer an explanation
where appropriate.
5. Write a logical question that stems from doing the experiment.
Experiment 1
In this experiment you will expose the gas released from an extinguished candle to a burning match. Will the gas released from the wick when a candle is extinguished burn?
1. Light the candle.
2. Allow the candle to burn for about a minute.
3. Light a match.
4. Blow the candle out.
5. Place the lit match about one inch above the wick in the path of the gas ("smoke") which is being released by the extinguished candle. If nothing happens, try it again, placing the lit match a little closer to the wick. If something does happen, see if the same thing happens if the lit match is held even higher above the wick.
6. Record your observations in your lab notebook.
7. Write a logical question that stems from doing the experiment in your lab notebook.
Experiment 2
In this experiment you will investigate lighting the candle when a piece of aluminum is placed over the wick. Will the candle still burn if a piece of aluminum foil is placed over the wick before the candle is lit?
1. Cut a piece of aluminum foil into a 3cm square.
2. Use your pen or pencil tip to punch a hole through the center of the foil. Make
the hole about the same diameter as the diameter of the wick.
3. Place the aluminum foil over the wick.
4. Light the wick and observe for several minutes.
5. Record your observations in your lab notebook.
6. Write a logical question that stems from doing the experiment in your lab notebook.
Experiment 3
What changes take place to an Erlenmeyer flask if it is held over a burning candle?
1. Light the candle.
2. Lift a clean, dry Erlenmeyer flask with both hands, and place it inverted over the candle as shown below. The rim of the flask should be roughly level with the base of the wick of the candle. Observe for 1-2 minutes. Make sure you observe the flask as well as the flame carefully!
3. Lift the flask off of the candle and place upright (right side up) on the lab bench. Be careful — the flask will be hot!
4. Observe the flask carefully, and record your observations. If you would like to repeat the experiment, allow the beaker to cool first.
5. Record your observations in your lab notebook.
6. Write a logical question that stems from doing the experiment in your lab notebook.
Experiment 4
In this experiment you will see what happens when a beaker encloses a burning candle. What happens if an Erlenmeyer flask is placed over a burning candle?
1. Light the candle.
2. Lift a clean, dry Erlenmeyer flask with both hands, and place it inverted over the candle as shown below. The flask should rest on the bottom of the fingerbowl completely covering the candle. Observe until no more changes are apparent. Make sure you observe the flask as well as the flame carefully!
3. Lift the flask off of the candle and place upright (right side up) on the lab bench. Be careful — the flask will be hot!
4. Observe the flask carefully, and record your observations.
5. Allow the beaker to cool, then clean the beaker thoroughly with soap, water, and a brush.
6. Record your observations in your lab notebook.
7. Write a logical question that stems from doing the experiment in your lab notebook
Experiment 5
In this experiment you will see what happens when a beaker encloses a burning candle surrounded by water. What happens if an Erlenmeyer flask is placed over a burning candle that is surrounded by water?
1. Fill the fingerbowl with water to a depth of 2cm.
2. Light the candle.
3. Lift a clean, dry Erlenmeyer flask with both hands, and place it inverted over the candle as shown below. The flask should rest on the bottom of the fingerbowl completely covering the candle.
4. Observe until no more changes are apparent. Make sure you observe the flask, the water and the flame carefully!
5. Lift the flask off of the candle and place upright (right side up) on the lab bench. Be careful — the flask will be hot!
6. Observe the flask carefully, and record your observations.
7. Allow the beaker to cool, then clean the beaker thoroughly with soap, water, and a brush.
8. Record your observations in your lab notebook.
9. Write a logical question that stems from doing the experiment in your lab notebook
Experiment 6
What happens to the mass of a candle as it burns?
1. Determine the mass of a candle and fingerbowl.
2. Let the candle burn for 4 minutes.
3. Determine the mass of the candle and base again.
4. Record your observations in your lab notebook. (Remember to record accurate masses and their units.)
5. Write a logical question that stems from doing the experiment in your lab notebook
Post- lab Questions and Tasks
Answer the post-activity questio ns in your laboratory notebook after all your observations and questions. Title this section POST LAB ANSWERS. Use complete sentences that begin by restating the question as a sentence.
1. Write in numbered steps, the apparent process of a candle burning. (Assume the candle is burning.)
2. What substance (the wick or the wax) is the primary fuel for a burning candle? Supply sufficient evidence from your observations to support your answer.
3. What is the identity of the "smoke" that is released when a candle is extinguished? Supply sufficient evidence to support your answer.
4. What is the role of the wick in a burning candle? Supply sufficient evidence to support your answer.
5. The primary elements in a candle are carbon and hydrogen. What happens to the carbon when the candle burns?
6. What happens to the hydrogen when the candle burns? What evidence do you
have to support your answer?
7. Write two questions about the burning of a candle that were unanswered in this activity.
Summer 2010 6 of 6