Investigation of Combustion of Alcohols

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Investigation of Combustion of Alcohols

Aim

The aim of this experiment is to investigate the combustion of various alcohols. The alcohols will be burnt to heat up a test tube of water, I aim is to find out how much energy is produced when burning the following alcohols: Methanol, Ethanol, Propanol, Butanol, and Pentanol. Any form of burning is an exothermic reaction (heat is given out), this means that the reactants energy is higher than that of the product. Alcohols react with oxygen in the air to form water and carbon dioxide.

Prediction:

When bonds are broken, energy is absorbed by the system (endothermic) and when bonds are formed, energy is released (exothermic). When alcohols are burnt, the reaction is always overall exothermic, therefore, more energy is being released than is being consumed.

Thus, my prediction is that each alcohol will burn exothermally and therefore the temperature of the water will rise.

The larger the alcohol molecule, the more bonds will be broken and formed, and therefore the more heat will be produced, so I think that Methanol will be the alcohol to combust the least, followed by Ethanol, Propanol and Butanol, then finally Pentanol, combusting the most.

Preliminary Work

Before carrying out my final experiment, I have to carry out a preliminary experiment, to determine the most efficient method to use, and on what scale.

Preliminary Results

My preliminary results enabled me to decide on 30 degrees as a suitable water temperature change, as this allowed a large enough change in mass of the alcohol, but was not too time consuming. It also helped me decide to experiment with each alcohol twice, this will ensure accurate results just one could be unreliable.

Apparatus

* 5 Alcohols, Methanol, Ethanol, Propanol, Butanol and Pentanol.

* Test tube

* Thermometer

* Water

* Draught preventers (chemistry books)

* Clamp

* Heat proof mat

* Measuring cylinder

Method

Collect and set up apparatus as shown in the diagram.

Measure __ml of water in the measuring cylinder.

Pour into test tube.

Place thermometer in the water and record the starting temperature.

Weigh alcohol container, record weight for before the experiment.

Make sure all safety precautions are in place (safety goggles, heat proof mat).

Ignite alcohol containers wick.

When the temperature has rose 30 degrees, put out flame using lid.

Weigh the alcohol container and record weight after experiment.

Repeat twice for each alcohol.

Variables to be kept the same

* Height above the mat at which the test tube is clamped (__cm)

We keep this the same because if the flame was closer to the test tubes on some, than on others, it would not be a fair test, some would obtain more heat than others.

* Temperature change

Changing this would leave nothing to measure how long to burn the alcohol.

Results

To work out the results, averages of the masses were taken from both the experiments, however, some of the end results proved to be inaccurate, therefore, only the results from the first experiment were used.

Changes in mass

Before (g)

After (g)

Before (g)

After (g)

Average Change/ Change in Mass (g)

Methanol

181.05

178.63

169.07

168.06

1.715

Ethanol

163.80

161.84

N / A

N / A

1.96

Propanol

171.80

171.07

N / A

N / A

0.73

Butanol

192.78

192.19

216.05

215.19

0.775

Pentanol

174.34

173.69

N / A

N / A

0.65

Changes in temperature

All increase by 30°C, except for Pentanol, the results for which were given to us, as the experiment would be too dangerous to conduct in the lesson.

Before (°C )

After (°C )

Before (°C)

After (°C)

Change in temp (°C)

Methanol

20

50

18

48

30

Ethanol

20

50

20

50...
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