LAB: Sources of the Flame
Students taking Scholars Online AP Chemistry in the fall should consult with the instructor for additional AP lab instructions to use for this experiment.
Goal: To closely observe the flame of a burning candle
- one parafin taper or votive candle
- one beeswax candle
- one oil lamp (decorative) or alcohol lamp (may come as part of a chemistry set)
- strong flashlight, slide projector, or direct sunlight
- white paper screen
ALWAYS USE EXTREME CAUTION WHEN WORKING AROUND OPEN FLAMES!
Be sure to review the safety information before performing each experiment.
- Decide how you will take your notes (review the NOTES information from the introduction).
- Examine your candles (and the oil lamp or alcohol lamp if you use one) and write a careful description of each one.
- What kinds of information do you think will be important (size, shape, composition, etc.)?
- Is the size of the candle or lamp of interest? What dimensions and units will you use to measure these?
- Is candle color (or oil color) important?
- What information should you collect about the material the candle is made of?
- What information should you collect about the type of fuel used in the lamp?
- Now place one of the candles in an area where there is no draught, and light it. Allow it to burn for several minutes, so that the candle substance has warmed up and the flame has settled to a steady state.
- Observe the flame. How large is it? What is the shape of the flame? Can you find the dark and bright areas Faraday describes?
- Repeat your observations for the flame of the other candle(s) and lamp(s).
- Now compare the flames: is one brighter, steadier, larger than the others?
- Blow each candle out and allow it to cool.
Testing an hypothesis
- Based on your initial observations, predict the rate at which each of your candles will burn compared to the others (slowest, more slowly, faster, fastest). Record your prediction.
- Mark each candle 1/4" below the top--you may simply want to put a small gouge in the side of the candle.
- Relight your candles simultaneously (you may want help to do this) and make a note of the time.
- If you cannot light your candles simultaneously so that you can conduct this test under the same conditions for all candles, use a stopwatch to time how long it takes each candle to burn to the mark. Note any changes in each candle's environment that might affect the rate at which it burns, such as increased drafts, higher temperatures, etc.
- Using your clock or stopwatch, note the time when each candle burns down to the mark. Do the different candles burn at different rates? What do you think might cause differences in the rates?
- Tilt each candle and allow the "cup" which contains the liquid wax to become gutted and irregular. How does the gutting affect the steadiness of the flame?
Observing the shadow
- Set up a screen so that your light source (strong flashlight, slide projector lamp, or direct sunlight) will fall through the candle flame onto the screen. The candle should be fairly close to the screen (you want a sharp image), but not so close that you set your screen on fire!
- Carefully observe the image on the screen. Can you see the shadow cast by the flame? Can you see the air currents around the flame? What is the best way of capturing information about the shadow and currents?
Write a report of all your observations and post it to the assignment module in the Moodle by 6pm EDT Monday, before our next class. Your report should include
- A list of the materials you actually used.
- A brief description of your procedure, with notes on any major changes you made to the suggested procedure above.
- Any other observations you think interesting or important.
- Your conclusions about whether the candles burned at different rates, and your best explanation as to why they did or didn't. Organize your answers to the questions asked in my procedure directions, and include these in your analysis.
Read and evaluate at least one other student's report. As you read, think about
- how can the observation methods be improved?
- How did the observer choose what to observe?
- Are the observations useful from a scientific point of view? Why do you think so (or not think so)
- how can the report be improved? [One of the requirements for good science is good communication--science is, in many ways, a community effort].
- Did the observer explain his or her methods, materials, and procedure clearly?
- Do you have enough information to repeat the observer's observations for yourself, so that you can compare results?
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