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Investigation into Energy Released From Burning Various Alcohols.

Extracts from this document...

Introduction

Andrew Lyons

Investigation into Energy Released From Burning Various Alcohols

Planning

In this investigation, I will investigate the energy released from different alcohols when they are burnt.  I will be using the following alcohols:

Methanol

Ethanol

Propan-2-ol

Butan-1-ol

Pentan-1-ol

I will be burning the alcohols in spirit burners, with a beaker of water above.  I will use the temperature of the water, change in mass of the spirit burner and the specific heat capacity of water to work out the amount of energy released.  The reaction that occurs when burning alcohols is exothermic, and so the water in the beaker will absorb this heat energy.

The variables that could affect the investigation are listed here:

  • Types of Alcohol
  • Isomers of Alcohols
  • Type of Container (I.e. glass, plastic)
  • Time left for Alcohol to Burn
  • Height of Water above flame
  • Wick length on spirit burner

An alcohol has the general formula of: Cn H2n+1 OH

So, for example, the formula for Ethanol is C2H5OH, and the formula for Propan-1-ol/Propan-2-ol is C3H7OH.  Each alcohol has a different amount of Carbon (C) and Hydrogen (H) atoms, and this will affect the energy released by each separate one.  The different isomers of each alcohol may also affect the results.  An isomer is another variation of an alcohol, which has the same chemical formula, but a different molecule structure, and different physical properties.  This means that different isomers of the same alcohol may release different amounts of energy when burnt.

Source: Encarta Encyclopaedia 2003

The type of container will affect the results, and may make the test unfair.  Some of the energy given off will be taken in by the container, and the material the container is made from will affect how much of the energy is absorbed.

...read more.

Middle

I will wait a few seconds, and then take a measure from the thermometer for temperature.  I will then measure the mass of the spirit burner (making sure to keep the cap on).  I will record both these values.I will repeat the above steps, using the alcohol methanol, two more times to get repeated results.  When I have finished repeating the methanol results, I will collect a different spirit burner with ethanol in it.  I will then repeat all of the above steps once more, but this time using ethanol rather than methanol.I will repeat the experiment using ethanol two more times after the first, and then move onto the next alcohol, propan-2-ol.  When I have repeated propan-2-ol two more times after the first, I will move onto butan-1-ol.  After three butan-1-ol results, I will move onto the final alcohol, pentan-1-ol.Once I have all my results recorded, I will clear away the apparatus.

To keep the investigation safe, I will have to check a few things:

  • The water does not get too hot.
  • The Bunsen burner and spirit burner are kept away from places where they may easily be knocked.
  • The wick of the spirit burner is on firmly.  If it is not, then it may catch fire.
  • I will wear safety goggles to protect my eyes.
  • Any loose bodily articles are firmly secured, so they do not set alight.

Results

NOTE: Anomalous results highlighted in RED

After completing the investigation, I got the following results for temperature of the water and the mass of the spirit burner:

Attempt

Alcohol

Start mass of spirit burner and cap (g)

End mass of spirit burner and cap (g)

Change in mass (g)

Temp water at start ºC

Temp water at end ºC

Temp Rise

1

Methanol

187.95

186.55

1.40

23

50

27

2

186.55

185.14

1.41

22

49

27

3

185.14

183.80

1.34

22

48

26

1

Ethanol

180.83

179.30

1.53

22

62

40

2

179.30

177.74

1.56

22

62

40

3

177.79

176.15

1.64

22

57

35

1

Propan-2-ol

194.69

193.65

1.04

19

41

22

2

193.07

192.05

1.02

16

41

25

3

197.94

197.21

0.73

17

38

21

1

Butan-1-ol

172.72

171.80

0.92

18

48

30

2

171.10

170.14

0.96

18

49

31

3

170.14

169.23

0.91

19

49

30

1

Pentan-1-ol

164.87

164.18

0.69

18

41

23

2

164.18

163.49

0.69

18

39

21

3

163.49

162.81

0.68

18

42

24

The mass was measured with a precise balance for accurate results, and the temperature with a thermometer.  To get the values for change in mass and temperature rise, I will subtract the lower value from the higher value.

Attempt

Alcohol

Energy Liberated (Kj)

Kj per mole

Average Kj per mole

1

Methanol

9.07

207.36

2

9.07

205.89

207.29

3

8.74

208.62

1

Ethanol

13.44

404.08

2

13.44

396.31

400.19

3

11.76

329.85

1

Propan-2-ol

7.39

426.46

2

8.40

494.12

500.17

3

7.06

579.95

1

Butan-1-ol

10.08

810.78

2

10.42

802.90

811.12

3

10.08

819.69

1

Pentan-1-ol

7.73

985.60

2

7.06

899.90

976.36

3

8.06

1043.58

...read more.

Conclusion

I would use the same isomer of alcohol each time, so that I would get consistent results.  I would also measure the energy in other items such as the beaker, so that I could get much more accurate results, and this would allow me to form an even firmer conclusion.

If I were to further extend this investigation, I could investigate the other variables.

The main variable is isomers of the alcohols.

The method for investigating isomers would be almost identical to this investigation.  I would simply replace the 1-ol isomers with 2-ol.  I would predict that the 2-ol isomers would release less energy than the 1-ol isomers.  The results from this investigation suggest this, as more bonds must be broken, therefore using more energy.

I would also compare the 2-ol results with the results from this investigation, and I would also work out new theoretical results so that I could form a conclusion, and see how the different isomers vary from each other.

Another variable I could investigate is the time left for the alcohol to burn.  To investigate this, I would use an identical set up to my current investigation.  I would, however, repeat the investigation several times leaving the alcohol to burn for more or less time.  I would have a range of results which I could compare to come to a conclusion.  I would predict that as you increase the time left for the alcohol to burn, the energy released would increase.  If you increase the burning time, then you are increasing the amount of time there is for reactions to take place, and more bonds will make and break.  As you increase the number of bonds that are made, you also increase the energy that is released, as making bonds releases energy.

...read more.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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Here's what a teacher thought of this essay

4 star(s)

**** A sound report that has made good use of the collected data but could be improved by greater consideration being given to the evaluation.
To improve
Planning
The plan needs a thorough risk assessment to be included. It would help if greater consideration were given to how to limit heat loss in the experiment during the planning stage.
Carrying out
Valid data seems to have been recorded but some headings in tables are misleading or missing key columns and units. The values calculated do not seem to agree with published data.
Conclusion and Evaluation
The conclusion makes some reference to the relevant scientific theory and refers to possible anomalies. Whilst there are some ideas for extending the work there are no suggestions included that would modify the apparatus to help improve the main problem of heat loss.

Marked by teacher Stevie Fleming 15/10/2013

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