April, 2003, Middle School Experiment:

Burning Questions

- Purpose
- Background Information
- Equipment & Supplies
- Experimental Procedure
- Data Analysis
- Conclusions and Extensions

Ohaus ScoutTM II Balance
(model #SR2020)

Ohaus Balance

seltzer graphic
Purpose:

Students will investigate the combustion of a candle and measure how the candle’s mass changes as it burns.

*Note: This experiment requires DataStudio version 1.8.5, available approximately May 1, 2003, as a free download from store.pasco.com/forms/DSdownload.cfm.

Background Information:

Although evidence suggests candles were used as far back as ancient times, little is known of the exact origins of candles. The ancient Egyptians may have used rushes soaked in tallow (animal fat) as candles, but the Romans are credited with first developing the wick candle. Over the years candles have been made from a variety of substances, including tallow, beeswax, wax from bayberries and spermaceti (obtained from sperm whale oil). Today most candles are made from paraffin wax and stearic acid.

As a candle burns, it reacts with oxygen (O2) in the air to produce energy (heat and light), carbon dioxide (CO2) and water (H2O). Other products, including soot, may also form.

Consider generating a list of questions for students to investigate that will give them insight into the physical and chemical processes occurring as a candle burns. For example,

  • How does the temperature of the flame vary from the top to the bottom?
  • Is there liquid formed during the burning of the candle?
  • Is the top of the candle level, concave or convex while burning?
  • Does the wick or the wax burn, or both?

Hypothesize: Predict what will happen to the mass of a candle as it burns?

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Equipment and Supplies:

For each lab group:

  • Ohaus ScoutTM II Balance (model #SR2020)
    (Note: Ohaus Scout Pro Balance, available spring 2003, will also be compatible)
  • Candle
  • Aluminum foil
  • Safety matches

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Experimental Procedure:

Software & Probeware Setup
  1. Plug the Ohaus electronic balance into an electrical outlet and connect it to the computer using the 9-pin serial connector (RS232 cord) supplied with the balance.
    * Note: The cable is unidirectional; be sure to plug the labeled "scale" end into the balance. If the cable is plugged in the opposite way, the balance will blink continuously once the power is turned on and you will have to reverse the cable.

      ScienceWorkshop users: Unplug your 500 interface from the computer and connect the Ohaus balance in its place.

  2. Turn the power on to the balance.

  3. Launch the DataStudio program and click the Setup button ( ) in the main toolbar to open the Experiment Setup window.

      ScienceWorkshop users: Click the Change button ( ) and choose "PASPORT" when prompted by the dialog box that requests "Please Choose Data Source." Then reopen the Experiment Setup window. (This additional step is necessary because the Ohaus balance is only compatible with PASPORT.)

  4. Click the Add Ohaus Mass button. The Ohaus balance icon will appear in the Summary window and a graph of Mass vs. Time will be automatically added to the Graph window.

  5. Close the Setup window. Resize the graph display as needed.


Data Collection & Recording

  1. Obtain a small piece of aluminum foil to use as a candle base. Light the candle and allow some wax to drip onto the foil. Use the melted wax as a "glue" to secure the candle to the foil base. (Be sure the foil piece is large enough to prevent melted wax from dripping onto the balance pan.)

  2. Blow out the candle and place the candle and foil base on the balance pan.

  3. Click the Start ( ) button to begin recording data.

  4. After 10 seconds, carefully light the candle wick.

  5. Allow the candle to burn for approximately 15 minutes.

  6. Click the Stop ( ) button to end data collection.


Data Analysis:

  1. Examine the Graph Display to view your data, using the Scale to Fit button ( ) in the Graph toolbar to resize the axes as needed.

  2. Compare the rate of mass decrease and explain reasons for the change.

  3. How many physical changes can your students identify during the experiment?

Conclusions and Extensions:

  1. What observations suggest that combustion is a chemical change?

  2. How might the rate of mass decline be different if different-size candles were used? Try a short, thick votive candle compared to a taller taper candle. Does one shape of candle burn more quickly than another?

  3. Compare candles made of different types of wax, i.e. paraffin vs. beeswax.

  4. What effect does covering the candle with a beaker have? Why?