Heats of Combustion of Alcohol

Mark Wong 11N

Aim:

To find a pattern in the heat of combustion of number of fuels.

Apparatus:

* Clamp Stand

* Copper Can

* Thermometer

* 6 different alcohols – methanol, ethanol, propan-1-ol, butan-1-ol, pentan-1-ol and hexan-1-ol

* Matches

* Heat proof mat

* Aluminum foil

* Rubber band

* 100ml of water – for each alcohol

* Measuring cylinder

* Measuring scale

Diagram:

Method:

1. Collect and set up equipment as shown in diagram

2. Collect the first alcohol on the list (methanol)

3. Measure water to 100ml and pour into copper can

4. Measure temperature of water and record on a table

5. Measure whole weight of the alcohol excluding the cap of the bottle of alcohol and record the weight

6. Light the alcohol with a match and stir the water inside repeatedly

7. Stop experiment after the temperature has increased by 300c

8. Reweigh the mass of the alcohol and record

9. Repeat the test 3 times for a fair and meaningful result

10.Repeat the experiment with all the other alcohols

Variables/Fair Test:

In order to obtain a fair test the following will be done

1. Use a measuring cylinder to measure 100ml of water]

2. Use a measuring scale to measure the mass of each alcohol (excluding the cap provided with the bottle)

3. Make sure each alcohol is experimented 3 times so that an average can be calculated for a more meaningful result

4. Follow the order of alcohol according to the list (the order of the structures of the alcohols)

5. Make sure the aluminum foil is covering the flame of the fuel as much as it can without being burnt

6. Make sure each experiment is ended immediately when the temperature of the water rises up by 300c

7. Make sure for each experiment the bottom part of the copper can is always 8cm above the flame of the burning fuel

Results:

Test 1

Alcohol

Starting water temp. 0C

Finishing water temp. 0C

Weight of alcohol before (g)

Weight of alcohol after (g)

Difference in mass (g)

Methanol

26

56

197.86

194.66

-3.2

Ethanol

27

57

248

245.8

-2.2

Propan-1-ol

22

52

224.91

223.13

-1.78

Brutan-1-ol

25

55

269.54

267.56

-1.98

Pentan-1-ol

25

55

223.94

221.5

-2.44

Hexan-1-ol

27

57

239.32

238.02

-1.3

Test 2

Alcohol

Starting water temp. 0C

Finishing water temp. 0C

Weight of alcohol before (g)

Weight of alcohol after (g)

Difference in mass (g)

Methanol

26

56

195.86

192.74

-3.12

Ethanol

27

57

247

244.11

-2.89

Propan-1-ol

24

54

223.63

221.18

-2.45

Brutan-1-ol

26

56

368.31

365.82

-2.49

Pentan-1-ol

27

57

212.37

210.81

-1.56

Hexan-1-ol

28

58

238.01

236.67

-1.34

Test 3

Alcohol

Starting water temp. 0C

Finishing water temp. 0C

Weight of alcohol before (g)

Weight of alcohol after (g)

Difference in mass (g)

Methanol

25

55

189.84

185.52

-4.32

Ethanol

25

55

242.5

239.08

-3.42

Propan-1-ol

27

57

240.49

238.28

-2.21

Brutan-1-ol

27

57

263.32

261.19

-2.13

Pentan-1-ol

27

57

211.07

209.01

-2.06

Hexan-1-ol

28

58

241.57

239.43

-2.14

Average from the 3 tests

Alcohol

Average mass change (g)

Methanol

3.55

Ethanol

2.84

Propan-1-ol

2.15

Brutan-1-ol

2.20

Pentan-1-ol

2.00

Hexan-1-ol

1.59

Calculations:

Mass of water being heated – 100cm3 = 100g

Specific heat capacity of water – 4.18 J0c -1g1

Change in temperature of water – 300c

The following formulas were used to calculate the Energy change in water and the No. Of joules one gram of fuel produces

Amount of energy (J) given out by fuel = Q = mcT

Where:

Q= energy change in Joules

M=mass of water being heated in grams

C=specific heat capacity of water

T=change in temperature in 0c

Energy change in water = _J = 100 x 4.18 x _0C

No. Of joules one gram of fuel produces = _J/_g = _J/g

Table of Energy change in water and No. Of joules one gram of fuel produces

Alcohol

Energy change in water (J)

No. Of joules per g of fuel produces (J/g)

Methanol

12540

3532

Ethanol

12540

4415

Propan-1-ol

12540

5832

Brutan-1-ol

12540

5700

Pentan-1-ol

12540

6270

Hexan-1-ol

12540

7887

Graph – on a separate sheet

Graph shows the Number of Joules per Gram produces

Conclusion:

According to the results shown in the table and graph a pattern is present. As we can see on the graph the line of Number of Joules per gram of fuel produces as we go down from the list starting from Methanol to Hexan-1-ol the line increases. Although there is a slight misplacement where from Propan-1-ol to Brutan-1-ol the line slightly decreases and increases again from Brutan-1-ol to Pentan-1-ol, the misplacement does not affect the overall results. The misplacement may be from human error such as mistakes from recording results, room temperature change (whether air conditioning was powered on during a certain experiment through a certain alcohol) or measuring errors of the amount of water and water temperature before and after the experiment. From the results in the graph I can now state that as the structure of the alcohol increases, the energy that the alcohol produces increases. Therefore according to theory a perfect graph would show a positive straight line through the origin (direct proportionality).

Evaluation:

Although no hypothesis has been done, the results should be reliable. This is because this experiment was carefully planned and later on followed on the plan to do the experiment. Each experiment of each alcohol was repeated 3 times in order to obtain accurate and fair results. Calculations were done by using a calculator, and I have followed the formulas given in the beginning of planning the experiment. I have also followed the instructions of producing a fair test. The main problem of this experiment was he conditions we did the experiment in. There was a slight lack of time for the experiments to be done; the experiments could be repeated more in order to obtain an even more accurate result and better evidence would be shown if the experiment were to be repeated. The room temperature should be fixed; this is because the room temperature also affects the measurements on the thermometer therefore a fixed temperature (either air conditioning to be powered on or off).

Also if I had more time, I would calculate the number of Joules that one mole of fuel would produce. In that way I can compare the experimental results (Joules/grams) with the theoretical results (Joules/moles). If I had more time I would do research on this experiment before I start planning and proceed to this experiment, this way I would have more background knowledge of the experiment and will not suffer as much without knowing the theory of this experiment. A hypothesis can then be done if research and further knowledge of this experiment existed before, which then means a prediction can be made and compared to theory.