Heat of Combustion Experiment

Alkanols Heat of Combustion

Aim: To determine the molar heat of combustion of methanol, ethanol and 1-propanol

Materials:

• 3 spirit burners, one containing methanol, one containing ethanol and one containing 1-propanol.

• A thermometer

• A copper calorimeter

• 100 ml measuring cylinder

• Retort stand and clamps

• Stopwatch

• Matches

• Electronic balance

Safety assessment:

• This experiment contains flammable materials remove loose clothing such as ties which could be set alight.

• Wear safety glasses!

• Ensure equipment placement is safe and does not danger nearby students.

Method:

1. Set up the experiment as shown in the diagram below.

2. Measure exactly 100 milliliters of water using the measuring cylinder and carefully pour it into the Copper calorimeter. Put the thermometer in the water to measure the temperature of the water.

3. Weigh the spirit burner and record the mass

4. Record the temperature of the water in the Copper calorimeter.

5. Pull the cap off the spirit burner and light the cloth wick remembering to start the stopwatch as soon as the wick lights

6. Record the temperature of the water after 1, 2 and 3 minutes, at 3 minutes replace the cap on the spirit burner.

7. Reweigh the burner and record. Start experiment again at step 2 with a different alkanol. Each alkanol should be tested at least 3 times.

Results:

Methanol Test One Test Two Test Three

Mass before (g) 299.34 298.34 296.93

Temperature Before (°c) 23 24 23

After 1 Minute (°c) 30 33 29

After 2 Minutes (°c) 37 41 39

After 3 Minutes (°c) 43 48 49

Mass after (g) 298.34 297.29 295.99

Ethanol Test One Test Two Test Three

Mass before (g) 276.78 275.04 273.86

Temperature Before (°c) 23 23 23

After 1 Minute (°c) 29 32 33

After 2 Minutes (°c) 40 44 46

After 3 Minutes (°c) 53 55 58

Mass after (g) 275.42 273.86 272.63

1-Propanol Test One Test Two Test Three Test Four

Mass before (g) 189.63 187.64 186.08 184.81

Temperature Before (°c) 23 24 23 24

After 1 Minute (°c) 31 32 32 32

After 2 Minutes (°c) 44 45 42 42

After 3 Minutes (°c) 56 56 54 54

Mass after (g) 187.64 186.27 184.81 183.52

Conclusion:

Ethanol is the best for heating water as it heats the water in the shortest amount of time. Ethanol also uses less fuel to heat the water in the calorimeter.

Question: Calculate the heats of combustion per mole and per gram for each of the alkanols from the results. Show all working in the calculations in your report.

Methanol

Mass water: 100 gram

Temperature change: 23 °c

∆H=-mC∆T