Chemistry by Candlelight

Spend a romantic interlude in Olson Laboratories collecting  data and calculating values by candlelight.

In this experiment you will:

1.        Determine the rate equation for burning a candle.

2.        Calculate a Heat of Combustion for candle wax.

You will need a top-loading balance which reads to 0.001 g ( 1 mg), a candle, a clock with a second hand, an empty aluminum soda can,  a ring stand and clamp to hold the soda can and a 0-100 oC  thermometer.
Set the top-loading  balance to 0.000 g using the “TARE” button.  Light a candle and place it on the balance pan. Record masses to 1 mg, 0.001 g.  (Make sure that the candle does not set anything on fire!)

As the candle burns, you can see the decreasing weight of the candle recorded on the balance.

Obtain and weigh on a triple beam balance a dry aluminum soda can. This will serve as a calorimeter.

You will be assigned a candle and a volume of water to add to the “calorimeter”.
The water should be cold, 5-15oC.

Weight the Aluminum soda can + water.

Put your thermometer in the water.  Mix gently.

DO NOT PUT THE SODA CAN over the FLAME YET!

Clamp the soda can so that it will be directly over and just touching the candle flame when you start the experiment.

TO START the EXPERIMENT

1.      Put the soda can + water over the flame.

2.      Start timing

3.      Read the thermometer.

Do this all at once and record  temperature and weight at the  0 sec time.  Record on your DATA SHEET in ink!

Every 60 seconds, record the new weight.  Occasionally mix the water gently to insure the thermometer is reading the average water temperature. Also record the final temperature and time. End the experiment on an exact minute interval, i.e. 300 or 360 sec not 330 sec!
Collect data for 6 minutes or until the water temperature in the can reaches about 50 oC ,  which ever comes first.
Extinguish the candle flame by covering with a 600 mL beaker.  Observe and understand what happens.
Enter experimental data into a computer using…..    CANDLELIGHT   (PLAYCHEM icon on desktop)

CALCULATIONS
Sp Heat of Water  4.18 j/g oC

Use rule of Dulong and Petit to get Specific Heat of Al (AW = 26.982)
approx 25 j/mol oC = Molar Heat Capacity of most metals

Use the First Law of Thermodynamics to calculate Heat of Combustion.
Heat of Combustion is defined as the negative of the Enthalpy change.  Therefore Heats of Combustion for materials that “burn” are positive values.
ASSUME:  heat absorbed by can and water =  heat given off by the burning candle
temperature of water = average temperature of aluminum can

Using initial and final candle weights calculate an average rate for candle burning.
Using intermediate weight losses, come up with a rate equation for the burning candle.
Enter CALCULATIONS into computer. Get a GRADE for the experiment. Use CANDLELIGHT (PLAYCHEM icon on desktop)