Aninvestigationintothecombustionofalcohol

????* Weight the spirit burner for the mass before lighting it the lid must be on

* Make sure to weigh it with the lid to stop the alcohol from evaporating and record the results

????* Support the small copper over the spirit burner containing the methanol

????* Use the sheet burners to reduce the energy loss

* replace the spirit burner under the copper can a light the wick

* making sure that you are wearing your goggles, using the thermometer gently stir the water all time when the water is being heated

* keep on heating the water until the temperature has raised either 15oC - 20oC

* Extinguish the burner by putting the lid on. Keep stirring the water and note down the highest temperature it had reached

* Weigh the spirit burner using an electronic scale, and record it into the table.

* Finally repeat the experiment three times to make sure that your results are correct.

* Use fresh water every time you repeat

Alcohol

Initial mass (g)

Final mass (g)

Change of mass (g)

Average mass (g)

Initial temp oC

Final temp oC

Change of temp oC

Average temperature oC

Methanol

Methanol

Ethanol

Ethanol

Propan-1-ol

Propan-1-ol

Butan-1-ol

Butan-1-ol

* Repeat the experiment again however use different alcohol

* For each alcohol repeat the experiment three times for reliability

To find the enthalpy of combustion from the data:

You have to find the moles of the alcohol used. This will be the mass of the alcohol divided by its RMM(grams).

Find the amount energy released into the water from the burning alcohol:

Energy released= SHC x mass of water x temperature change

Results:-

Alcohol

Initial mass (g)

Final mass (g)

Change of mass (g)

Average mass (g)

Initial temp oC

Final temp oC

Change of temp oC

Average temperature oC

Methanol

68.98

66.38

.16

2.60

5

35

20

8.5

Methanol

69.36

66.70

.10

6

33

7

ethanol

61.76

60.60

2.60

.13

5

31

6

6

ethanol

60.60

59.50

2.60

6

32

6

Propan-1-ol

69.33

68.33

0.93

0.87

6

32

6

6

propan-1-ol

68.48

67.75

0.59

5

31

6

Butan-1-ol

76.50

75.57

0.77

0.76

7

34

7

6

butan-1-ol

64.01

63.42

0.73

6

31

5

Analysis:

Now I am going to calculate the amount of energy released in one mole for each alcohol by using the following formulas.

The RMM of each alcohol= the number of carbons + the number of hydrogen's in an

The moles used= change in mass/ RMM

The amount of energy released= SHC x mass of water x change of temperature

The amount of energy released in one mole= the amount of energy released / moles

Methanol:

The formula = CH3OH

The structural formula=

The RMM of the methanol= 12 + (3x1) + 16 + 1= 32

The moles used = change in mass/ RMM

The moles used = 2.60/32= 0.08125

The amount of energy released= SHC x mass of water x change of temperature=

4.2 x 200 x 18.5=-15540 joules (J)

The amount of energy released in one mole= the amount of energy released / moles

The energy released in one mole= 15540/0.08125= 191261.53 joules

91261.53/1000= -191.2615KJ per moles

I will repeat the same method for all the alcohols

My results on the amount of energy released in one mole:

Alcohols

The amount of energy released in one mole (KJ per mole)

methanol

-191.261

ethanol

-510.63

Propan-1-ol

-780.04

Butan-1-ol

-1148.72

Data books results:-

alcohols

the amount of energy released in one mole (KJ per mole-1

methanol

-726

Ethanol

-1367

Propan-1-ol

-2021

Butan-1-ol

-2676

As you can see from my results that as you increase the length of the carbon chain more bonds are being created therefore more energy is needed an example the methanol is has the shortest carbon chains in the experiment than all the other alcohols there is has released the lowest amount of energy this is because it did not need a lot of energy to break the bonds of the alcohol.

I'm going to compare the number of bonds between methanol and ethanol

Methanol ethanol

(C-C) = 0 (C-C) =1

(C-H)= 3 (C-H) = 5

(C-O)= 1 (C-O)= 1

(O-H)=1 (O-H)=1

If you look at the difference number of bonds between methanol and ethanol you can see that the (C-O) and the (O-H) bonds are fixed and they are the same in all the alcohols. As the alcohol increases the (C-C) bond increases by 1, and also as the alcohol increases the (C-H) bond increase by 2 this would make the alcohol release more energy to break the bonds.

As you can see from the table, the results I obtained from the experiment were not the same as the original data; this could have been due to errors related with the apparatus I had used.

Precision error:

The error involved here is said to be half a division of the instrumental scale.

A balance that measure to 0.01g

The error here is +/- 0.005g thus a reading of 272.63g of methanol from my experiment could be 272.631g, 272.632g, 272.633g etc.

The percentage error involved in this reading is 0.005 x 100/ 272.63= 1.83x 10-3 %

A thermometer that reads to a 1oC reading.

The error here is +/- o.5oC

Thus a reading of 17oC could be 17.5oC, 17.6oC, 17.7oC etc

The percentage error involved in this reading is o.5 x 100/17= 2.94%

A measuring cylinder that reads to 1cm3

The error here is 0.5 cm3

Thus reading of 100 cm3 could be 100.5 cm3 , 100.6 cm3 , 100.7 cm3 etc

The percentage error involved in this reading is 0.5 x 100/100=0.5%

However when reading a change in mass or temperature, the error reading will double. Thus a change in temperature of 20oC the percentage error involved would be 0.5x 100/20= 5%

And when measuring the change in mass the alcohol for example 1.00g of the percentage error involved would be 0.005 x 100/1.00= 0.5 x 2= 1%

From the precision error you can see that the error of equipment was not a lot. There could be error involved in the experiment which would affect the experiment.

Aspect of procedure

How can it lead to error

What effect does it have on the experiment

Weighing the fuel

If the fuel is not on it would lead for the alcohol to evaporate

This would increase in the enthalpy of combustion

Water is heated

Loosing the heat to the surroundings

This would decrease in the enthalpy of combustion

Not stirring frequently

The temperature wouldn't be constant and accurate

There would be change in the enthalpy of combustion

Incomplete combustion of alcohol

A different combustion reaction takes place with a different enthalpy combustion

The temperature rise of the water will be lower

Capping of burner after flame is extinguished

Alcohol will evaporate and the weight of the alcohol would not be accurate

This would lower the value of the enthalpy of combustion

Risk assessment:-

Type of alcohol

Risk

Precaution

Methanol

Highly flammable

Wear goggles and hand protection, no naked flames and all work in fume cupboard

Ethanol

Highly flammable and corrosive

Wear goggles and hand protection, no naked flames and all work in fume cupboard

Propan-1-ol

Highly flammable and irritant

All work must be done in the fume cupboard, wear goggles and also hand protection

Butan-1-ol

Highly flammable, causes series of damage to eyes, irritant and causes drowsiness and dizziness

All work must be done in the fume cupboard, wear goggles and also hand protection

References:

Salter's advance chemistry "chemicals ideas" second edition page 57-63, 63- 67

Cleaps Hazcards 2000

Nuffled data book page 113-115