Heat of combustion of alcohol investigation.docx

Chemistry Assigment Heat of combustion of alcohols investigation: Alcohol (aq) +O₂ (g) → CO₂ (g) + H₂O(g)

Focused research question: How does the change of the type of alcohol affect the amount of heat released during combustion? Hypothesis: My hypothesis is alcohols with more CH₂ (such as Octan-1-ol) will produce more heat energy than those with less (such as Methanol). This is due to the combustion of alcohols is an exothermic reaction, which means it produce heat during the reaction. More CH₂ means there will be more intermolecular forces, thus when the bonds break during the reaction, there will be more energy released. Independent variable: 

Type of alcohols (Methanol, Ethanol, Propan-1-ol, Butan-1-ol, Pentan-1-ol, Hexan-1-ol, Heptane-1-ol, Octan-1-ol)

Dependent variable: 

Temperature (°C)

How to make it a fair test: To make this experiment a fair test I have to pay attention to the following controlled variables and keep them the same throughout the experiment:    

Mass of water (60g) Mass of alcohol (170g) Time (10 minutes in total, 1 minute per recording) Room temperature (20°C)

List of materials (for one experiment):           

Alcohol in burner (Methanol, Ethanol, Propan-1-ol, Butan-1-ol, Pentan-1-ol, Hexan-1-ol, Heptane-1-ol, Octan-1-ol)(170g) Water (60g) Tin can Thermometer Stopwatch Stand Matchsticks Balance Safety glasses Gloves Apron

Method:

1.

Wear all protection outfits, including apron, safety glasses and gloves (as we are dealing with corrosive hydrochloric acid)

2.

Measure and record the room temperature

3.

Fill in the tin can with 60g of water, measured with electronic balance

4.

Fix the tin can with the stand

5.

Fill in the burner with 170g of alcohol, measured with electronic balance

6.

Place the burner under the flask

7.

Light up the burner and start recording time with stopwatch simultaneously

8.

Record the temperature of the waterchange every minute, from 0 to 10 minute

9.

Repeat steps 2 – 8, using different types of alcohol(Methanol, Ethanol, Propan-1-ol, Butan-1-ol, Pentan-1ol, Hexan-1-ol, Heptane-1-ol, Octan-1-ol)

10. Repeat steps 2 – 9 3 times to obtain average data to reduce random errors

Data collection and processing: st

Type of alcohol used Methanol Ethanol Propan-1-ol Butan-1-ol Pentan-1-ol Hexan-1-ol Heptane-1-ol Octan-1-ol

0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0

1 24.0 25.0 26.0 26.5 27.0 27.5 28.0 28.0

2 28.0 30.0 31.5 32.5 33.5 35.0 35.5 36.0

1 experiment Temperature (°C) (±0.1°C) Time (minute) 3 4 5 6 31.5 35.5 39.5 43.0 35.0 41.5 45.5 50.5 37.0 43.0 49.0 54.5 40.0 47.0 53.5 60.0 40.5 48.0 56.0 62.5 43.0 48.0 57.5 63.0 44.0 51.0 58.0 63.5 45.0 51.0 58.5 64.0

2 26.5 31.0 32.0 32.5 33.0 35.0 35.0 35.5

2 experiment Temperature (°C) (±0.1°C) Time (minute) 3 4 5 6 32.0 36.0 38.5 43.0 35.0 41.0 46.0 50.0 36.5 43.0 48.5 54.5 39.0 46.5 53.0 59.0 40.0 47.5 56.5 64.0 43.5 47.5 57.0 63.5 44.0 53.0 58.0 64.0 44.5 53.5 59.0 64.5

2 27.0 30.5 31.0 32.5 33.0 35.5 36.0 36.5

3 experiment Temperature (°C) (±0.1°C) Time (minute) 3 4 5 6 30.0 34.0 39.0 42.5 34.0 41.5 44.0 50.5 37.5 43.5 49.0 54.5 40.0 46.0 52.0 60.0 41.0 47.0 54.5 62.5 43.0 48.5 57.0 63.0 44.5 51.0 57.5 63.5 45.0 53.0 59.0 65.0

7 47.0 55.5 60.5 67.0 72.0 72.5 74.5 74.5

8 51.0 60.5 66.0 73.5 75.5 80.0 82.0 86.0

9 55.0 66.0 72.0 80.0 83.0 84.0 85.0 89.0

10 59.0 71.0 77.5 82.0 85.0 88.0 92.0 94.0

7 46.0 55.5 60.0 66.0 71.0 72.5 73.0 75.0

8 50.5 60.0 66.5 73.0 75.5 81.0 81.0 85.0

9 52.0 63.5 71.0 80.5 82.0 83.0 85.5 88.0

10 57.0 70.0 77.5 81.5 85.0 88.5 91.0 93.0

7 45.0 56.0 60.5 67.0 72.0 72.5 74.5 76.0

8 51.5 60.0 67.0 71.5 74.5 82.0 83.0 87.0

9 54.0 65.0 70.0 79.5 81.0 84.0 86.0 90.0

10 58.0 72.0 74.5 82.5 84.0 88.0 91.5 92.0

7 46.0 55.7 60.3 66.7 71.7 72.5 74.0 75.2

8 51.0 60.2 66.5 72.7 75.2 81.0 82.0 86.0

9 53.6 64.8 71.0 80.0 82.0 84.8 85.5 89.0

10 58.0 71.0 76.5 82.0 84.7 88.2 91.5 93.0

nd

Type of alcohol used Methanol Ethanol Propan-1-ol Butan-1-ol Pentan-1-ol Hexan-1-ol Heptane-1-ol Octan-1-ol

0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0

1 23.0 25.5 26.0 26.0 28.0 27.5 28.0 29.0

rd

Type of alcohol used Methanol Ethanol Propan-1-ol Butan-1-ol Pentan-1-ol Hexan-1-ol Heptane-1-ol Octan-1-ol

0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0

1 23.5 24.0 26.0 26.5 27.0 28.0 28.5 29.0

st

Type of alcohol used Methanol Ethanol Propan-1-ol Butan-1-ol Pentan-1-ol Hexan-1-ol Heptane-1-ol Octan-1-ol

0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0

1 23.5 24.8 26.0 27.0 27.3 27.7 28.2 28.7

nd

rd

Average( = (1 exp. + 2 exp. + 3 exp.)/3) Temperature (°C) (±0.3°C) Time (minute) 2 3 4 5 6 27.2 31.2 35.2 39.0 42.8 30.5 36.7 41.3 45.2 50.3 31.5 37.0 43.2 48.8 54.5 32.5 39.7 46.5 52.8 59.7 33.2 40.5 47.5 54.5 63.0 35.2 43.3 48.0 57.3 63.2 35.5 44.2 51.7 57.8 63.5 36.0 44.8 52.5 58.8 64.5

To visualize the data, I created the following graph:

I have also made a table to present the % of uncertainty in my experiment, by using the following formulas: st

nd

rd

Total error = 1 exp. + 2 exp. + 3 exp. = ±0.3°C % uncertainty = (total error x 100)/average temperature % uncertainty of the average temperature released during combustion of alcohols Type of alcohol Time (minute) used 0 1 2 3 4 5 6 7 8 Methanol 1.5% 1.3% 1.1% 1.0% 0.9% 0.8% 0.7% 0.7% 0.6% Ethanol 1.5% 1.2% 1.0% 0.8% 0.7% 0.7% 0.6% 0.5% 0.5% Propan-1-ol 1.5% 1.2% 1.0% 0.8% 0.7% 0.6% 0.6% 0.5% 0.5% Butan-1-ol 1.5% 1.1% 0.9% 0.8% 0.6% 0.6% 0.5% 0.4% 0.4% Pentan-1-ol 1.5% 1.1% 0.9% 0.7% 0.6% 0.6% 0.5% 0.4% 0.4% Hexan-1-ol 1.5% 1.1% 0.9% 0.7% 0.6% 0.5% 0.5% 0.4% 0.4% Heptane-1-ol 1.5% 1.1% 0.8% 0.7% 0.6% 0.5% 0.5% 0.4% 0.4% Octan-1-ol 1.5% 1.0% 0.8% 0.7% 0.6% 0.5% 0.5% 0.4% 0.3%

9 0.6% 0.5% 0.4% 0.4% 0.4% 0.4% 0.4% 0.3%

10 0.5% 0.4% 0.4% 0.4% 0.4% 0.3% 0.3% 0.3%

Conclusion: From the graph we can clearly see a trend that shows as alcohol with more CH₂ used in the experiment, the temperature of the water in the tin can increases. Therefore this result proves that my hypothesis at the beginning of this investigation was correct. Because the combustion process of alcohol is an exothermic reaction, as I increase CH₂ there will be greater intermolecular forces, thus when the bond breaks during the reaction it will release more energy. There is also an interesting trend that the heat increase difference gradually decreases as we use alcohol with more CH₂ attached to it. This can be explained with incomplete combustion. If there were insufficient oxygen during the combustion, the alcohol cannot release all the energy stored in the bonds.

Evaluation: Although I have tried my best to keep the experiment to carry out accurately by providing similar conditions for thereaction by using computer program, however there are still some places of this experiment that I can improve next time if I carry out a similar experiment in real life: 1.

2.

3.

4.

5.

Systematic errors – as we can see from my results, the percentage of uncertainty vary from 0.3% to 1.5%. This means I could not receive very precise data for me to analyze. This problem can be reduced if I will use the more precise measuring tools next time, such as digital thermometer, because this time I had to round of most of the results to one decimal place. However, I can argue that even though the data were not so accurate, but they did not affect the overall trend of the experiment. Random errors – random error is another important source of errors that might have affected my results, because the computer program I used is very realistic and provided different result each time. The most useful way to reduce the random errors is by repeating the experiment more times. By using more data in the process of calculating the average results, the random errors will have less effect on the trend that shows the heat released during the combustion of alcohols. Due to the fact that I was using a computer program, many effects from external factors were able to be prevented. However, if I was carrying out a real life experiment, I have to make sure the controlled variables to maintain the same during the process of reaction. For example, I need to carry out the experiment as quick as possible to reduce the effect of room temperature change on the reaction. Also as stated before, I will have to use precise tools to measure the variables, because observing them with eyes will not be as accurate as this computer program. Another area of improvement can be covering the top of the tin can during the reaction. Because during the experiment the surface of water was left open in the air, a rather large amount of heat energy escaped, thus lowering the temperature of the water. By sealing the top of the tin can next time, we can effectively reduce the amount of heat energy lost in the air. The last area improvement is providing enough oxygen for the alcohols to have complete combustion. As earlier I pointed out, the heat increase difference gradually decreases as we use alcohol with more CH₂ attached to it, which can be caused due to insufficient amount of oxygen and causing incomplete combustion. To prevent this problem from happening next time, it is important to provide enough oxygen next time to let all alcohols have complete combustion and produce heat energy.