CHEMISTRY

Exercise 1: Energy Content of Fuels In this experiment, you will make a simple calorimeter to determine the energy content in two fuels, diethylene glycol and paraffin wax. The energy content will be determined by burning each fuel and measuring the change in temperature of 200 mL of distilled water.

The following equation will be used to calculate the number of calories in each type of fuel:

p Q = T m c∆ × ×

● Q = amount of energy transferred to the water in calories (cal)

● ΔT = change in temperature (final temperature minus initial temperature) in ºC

● m = mass of distilled water (g)

● cp = specific heat capacity of water (1 cal / g × °C)

Note: The transfer of energy from the burning fuel to the water is not 100% efficient; some energy will be lost to the surrounding environment.

Calculating the Density (g/mL) of Water

Note: Under standard conditions (1 atm pressure and 25°C), 1 mL of water has a mass of 1 gram. It is unlikely that you will be performing this experiment at standard conditions, so it is necessary to calculate the density of water at your location.

1. Turn on the scale. Place the graduated cylinder on the scale and tare the scale so that it reads “0.0 g.”

2. Add exactly 10.0 mL of distilled water to the graduated cylinder and record the mass in Data Table 1 of your Lab Report Assistant.

3. Calculate the density of the water by dividing the mass of the water by the volume of the water and record in Data Table 1.

Determining the Energy Content of the Fuels

Fuel Canister

4. Use the graduated cylinder to measure and pour 200.0 mL of distilled water into the glass beaker.

5. Cut out two 20 cm x 20 cm squares of aluminum foil. Set 1 piece of foil aside (to be used in step 17). This will give you 3 pieces of foil: 2 pieces 20 x 20 cm, and 1 full sheet that was not cut.

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Experiment Energy Content of Fuels

6. Place the burner stand on one of the 20 cm x 20 cm squares of aluminum foil. See Figure 6.

Note: The burner stand is placed on a square of foil to protect the surface of the table.

7. Place the 250-mL beaker on the burner stand.

8. Place the thermometer in the water and allow it to equilibrate for 2 – 3 minutes. Record this initial temperature in Data Table 2 of your Lab Report Assistant, under “Initial temperature,” in the “Fuel canister” row.

9. Turn on and tare the digital scale, so that it reads “0.0 g.”

10. Place the fuel canister with the lid on the scale. Measure the mass in grams and record in Data Table 2 under “Initial mass of fuel” in the “Fuel canister” row.

11. Remove the cap from the canister and place the canister under the burner stand. Use the remaining large piece of aluminum foil (not the 20 cm x 20 cm piece put aside) to cover both the beaker (with the thermometer still in it) and the stand. Leave a little room open at the bottom to allow for air flow so that the fuel will have adequate oxygen to burn. See Figure 6.

Figure 6. Construction of calorimeter with foil canopy.

12. Carefully lift the foil off of the burner, and use a match or lighter to light the wick on the fuel canister. Replace the foil, and immediately start the timer.

Note: You may have to make adjustments to ensure that enough air can enter the foil canopy to allow the fuel to continue to burn.

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Experiment Energy Content of Fuels

13. Heat the water for 10 minutes and then carefully remove the foil and place the cap back on the fuel to extinguish the flame. Do not tighten the cap because it will be difficult to remove when it cools.

14. Quickly read the thermometer and record the temperature in Data Table 2 under “Final temperature” in the “Fuel canister” row.

15. Allow the beaker to cool in preparation for the next part of the experiment and then empty the water.

16. When the fuel canister has cooled enough to be safely handled, tare the scale and place the canister back on the digital scale to measure the final mass. Record the mass in Data Table 2 under “Final mass of fuel” in the “Fuel canister” row.

Tea Candle

17. The candle must be suspended from the bottom of the stand so that the flame is close to the wire mesh. Use the piece of foil that was set aside to fasten a hammock-like structure to the legs of the stand. Wrap each corner of the foil around the four legs on the stand, as shown in Figure 7. The candle should be about one inch from the bottom of the stand.

Figure 7. Construction of a “hammock” to suspend the candle.

18. Turn on and tare the digital scale so that it reads “0.0 g.”

19. Place the candle on the scale. Measure the mass in grams and record in Data Table 2 under “Initial mass of fuel” in the “Tea candle” row.

20. Place the candle in the hammock so it sits securely in place.

21. After the beaker has cooled, use the graduated cylinder to measure 200.0 mL of distilled water and pour the water into the beaker. Place the thermometer back into the water and

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Experiment Energy Content of Fuels

allow it to equilibrate for 2 – 3 minutes. Record the temperature in Data Table 2 under “Initial temperature” in the “Tea candle” row.

22. Place the beaker with the water on the burner stand.

23. Cover the experiment with the foil canopy. Adjust the canopy as needed, and make sure that it fits well, leaving a little room open at the bottom to allow for air flow so that the fuel will have adequate oxygen to burn.

24. Remove the foil canopy and use a match or lighter to light the wick of the candle while it is in the hammock. Replace the foil, leaving a small opening at the bottom so air can enter. Immediately start your timer.

25. Allow the candle to burn for 10 minutes.

26. After 10 minutes, carefully remove the foil, blow out the candle, and quickly read the thermometer. Record the temperature in Data Table 2 under “Final temperature” in the “Tea candle” row.

27. After the candle has cooled enough to be safely handled (the wax will have solidified again), disassemble the hammock and remove the candle.

28. Turn on the scale and tare it so the scale reads “0.0 g.”

29. Place the candle on the scale to measure its mass. Record the mass in Data Table 2 under “Final mass of fuel” in the “Tea candle” row.

30. Calculate the ΔT for each fuel type by subtracting the initial temperature from the final temperature and record in Data Table 3 of your Lab Report Assistant.

31. To calculate the number of calories of energy absorbed by the water (Q), use the equation:

● Use the density of water you determined in Data Table 1 to calculate the mass of 200.0 mL of water (multiply the density by 200).

● The specific heat capacity (cp) of water is 1.00 cal / g x °C.

32. Use the temperature change in the equation and calculate Q. Record the calories for both fuel types in Data Table 3 under “Calories absorbed by water.” For example, if the density of the water at your location was 0.95 g/mL and the temperature change was 20 °C, then your equation would be:

× × × ×o o

0.95g 1calQ = (20 C) (200mL ) = 3800cal mL g C

33. Using the mass data in Data Table 2, determine the total mass of fuel consumed by subtracting the final mass from the initial mass, and record the result in Data Table 3 under “Grams of fuel

p Q = T m c∆ × ×

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Experiment Energy Content of Fuels

consumed” for each of the fuel types.

34. For each fuel, divide the calories absorbed by the grams of fuel consumed to determine the amount of energy in calories released per gram of fuel. Record these values in Data Table 3.

35. When the beaker has cooled sufficiently, pour out the water, and clean up your work area.

36. Return all clean items to your LabPaq kit for future use.

Questions A. Which fuel was more efficient (produced more calories per gram)? Explain your answer.

B. Explain the difference in the efficiencies of the fuels you tested based on the chemical struc- tures of the fuels.

C. Conduct research on both diethylene glycol and paraffin wax; for each fuel, summarize in your own words in one or two sentences how these fuels are synthesized. Cite the sources that you use for your research.

D. What are the possible sources of error in this experiment? How could the errors be reduced in future experiments?

E. Research how different fossil fuels compare in terms of the amount of carbon dioxide released per kWh of energy. How much carbon dioxide is produced by burning a gallon of gasoline? A gallon of diesel? Cite the sources that you use for your research.

F. Compare the amount of carbon dioxide released in one year from burning coal to power 10, 65-watt incandescent bulbs with the amount released from powering 10, 13-watt compact fluorescent light (CFL) bulbs. Assume the bulbs are on four hours per day for 365 days. You will need to determine the kilowatt hours (kWh) used. First, multiply the wattage of the bulbs by the number of light bulbs to determine the total watts used in one hour. Then mul- tiply the result by time in hours to obtain the watt hours. Next, divide the result by 1000 to obtain kilowatt hours. On average, 2.1 pounds of carbon dioxide are released for every kWh of electricity produced.

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Experiment Energy Content of Fuels

Energy Comparison of Fuels Hands-On Labs, Inc. Version 42-42-0154-00-02

Lab Report Assistant This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Exercise 1: Energy Content of Fuels Data Table 1. Mass and Density of Distilled Water.

Mass of 10.0 mL of distilled water

(g)

Density of water

(g/mL)

Data Table 2. Calorimetric Data.

Fuel Source: Initial mass of

fuel (g)

Final mass of fuel (g)

Initial temperature

(°C)

Final temper- ature (°C)

Fuel canister: (di- ethylene glycol)

Tea candle: (paraf- fin)

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Experiment Energy Content of Fuels

Data Table 3. Calories Released per Gram of Fuel.

Fuel Type ΔT (°C) Calories absorbed by water (cal) Grams of fuel consumed (g) Calories/gram

Fuel canister: (di- ethylene glycol)

Tea candle: (paraf- fin)

Questions A. Which fuel was more efficient (produced more calories per gram)? Explain your answer.

B. Explain the difference in the efficiencies of the fuels you tested based on the chemical struc- tures of the fuels.

C. Conduct research on both diethylene glycol and paraffin wax; for each fuel, summarize in your own words in one or two sentences how these fuels are synthesized. Cite the sources that you use for your research.

D. What are the possible sources of error in this experiment? How could the errors be reduced in future experiments?

E. Research how different fossil fuels compare in terms of the amount of carbon dioxide released per kWh of energy. How much carbon dioxide is produced by burning a gallon of gasoline? A gallon of diesel? Cite the sources that you use for your research.

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Experiment Energy Content of Fuels

F. Compare the amount of carbon dioxide released in one year from burning coal to power 10, 65-watt incandescent bulbs with the amount released from powering 10, 13-watt compact fluorescent light (CFL) bulbs. Assume the bulbs are on four hours per day for 365 days. You will need to determine the kilowatt hours (kWh) used. First, multiply the wattage of the bulbs by the number of light bulbs to determine the total watts used in one hour. Then mul- tiply the result by time in hours to obtain the watt hours. Next, divide the result by 1000 to obtain kilowatt hours. On average, 2.1 pounds of carbon dioxide are released for every kWh of electricity produced.

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Experiment Energy Content of Fuels

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