To answer the research question, “Does the structure of an alcohol affect its standard enthalpy of combustion?”, a practical was carried out using a range of alcohols with different lengths of carbon chain, a spirit burner, a scale, a calorimeter, and 200ml of water. Analysis of the data concluded that the length of carbon chain is directly proportional to the standard enthalpy of combustion. This research is relevant to the global issue of alcohols being used as alternate fuels to prevent global warming. As a student, I am interested in pursuing this research question further as I want to work in the energy sector developing alternate fuels.

Independent Variable: length of the carbon chain of alcohol. 

• It is measured in number of carbon atoms. 

• The apparatus used to measure this is a scale. 

• The problem with measuring this variable is that the alcohols may not be pure.

• The range of values in this experiment can be expected to be between 1 and 5 carbon atoms as these are the alcohols being tested. 

Dependent Variable: standard enthalpy of combustion of the alcohols. 

• It is measured in joules. 

• The apparatus used to measure this is an enthalpy of combustion calorimeter. 

• The problem with measuring this variable is that the calorimeter may not be able to measure small changes in the enthalpy of combustion accurately. 

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Control Variables 

1. Temperature of the water. To keep the temperature of the water constant, the same temperature should be used each time the experiment is conducted. This will be done using a thermometer.

2. Mass of the alcohol. To keep the mass of the alcohol constant, the same amount of alcohol should be measured each time the experiment is conducted. This will be done using an electronic balance.

3. Volume of the water. To keep the volume of the water constant, the same volume of water should be used each time the experiment is conducted. 

4. Type of spirit burner. To keep the type of spirit burner constant, the same type of spirit burner should be used each time the experiment is conducted.

5. Time of the reaction. To keep the time of the reaction constant, the same amount of time should be used each time the experiment is conducted.

1. Measure out the same mass of alcohol for each length of carbon chain alcohol, and record the value

2. Place the measured alcohol in the spirit burner and light the burner.

3. Place the calorimeter over the flame of the spirit burner and wait until the temperature of the water increases by 10 degrees Celsius.

4. After the temperature of the water has increased by 10 degrees Celsius, turn off the spirit burner and remove the calorimeter.

5. Measure the mass of the alcohol again, and record the value.

6. Calculate the standard enthalpy of combustion using the mass of the alcohol before and after. 

7. Repeat the experiment for the remaining alcohols.

Limitations

1. The alcohols may not be pure, meaning the measurements of mass are not precise

2. The spirit burner may not be able to provide a consistent and even heat source.

3. The calorimeter may not be able to accurately measure the temperature of the water, leading to inaccurate enthalpy of combustion values.

Effect on Results

1. This may lead to inaccurate measurements of the mass of the alcohols, resulting in inaccurate enthalpy of combustion values

2. An inconsistent and uneven heat source from the spirit burner may lead to inaccurate enthalpy of combustion values.

3. An inaccurate measurement of the temperature of the water may lead to inaccurate enthalpy of combustion values.

Possible Improvements

1. Rather than using manufactured alcohols, the alcohols could be distilled in the lab first as a preliminary experiment. This would ensure purity of the alcohols.

2. Use a Bunsen burner with a more consistent and even heat source.

3. Use a thermometer to accurately measure the temperature of the water.

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