• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month

The Combustion of Alcohols and the factors affecting these reactions

Extracts from this document...

Introduction

The Combustion of Alcohols and the factors affecting these reactions Planning Aim: The aim of this experiment is to investigate the combustion of alcohols and how the different structures of alcohols affect the amount of energy given off. Alcohols: The general formula is CnH2n+1OH and n representing the number of carbon atoms in an alcohol molecule. So if I know the number of carbon atoms present this formula allows me to find the formula for every alcohol. From the simplest alcohol methanol, that has one carbon molecule, to pentanol with five carbon atoms. Throughout the combustion of the alcohols, the alcohols will react with the oxygen in the air. The word equation below represents this: Alcohol + Oxygen Carbon Dioxide + Water The table below shows the alcohols I will be using in this investigation: Alcohol No. of Carbons Formula Equation Methanol 1 CH3OH 2CH3OH(l) + 3O2(g) 2CO2(g) + 4H2O(g) Ethanol 2 C2H5OH C2H5OH(l) + 3O2(g) 2CO2(g) + 3H2O(g) Propanol 3 C3H7OH 2C3H7OH(l) + 9O2(g) 6CO2(g) + 8H2O(g) Butanol 4 C4H9OH C4H9OH(l) + 6O2(g) 4CO2(g) + 5H2O(g) Pentanol 5 C5H11OH 2C5H11OH(l) + 15O2(g) 10CO2(g) + 12H2O(g) To show the structure of these alcohols I am using the following diagrams illustrate this: Methanol CH3OH Ethanol C2H5OH Propanol C3H7OH Butanol C4H9OH Pentanol C5H11OH Variables: There are a number of variables that I have to consider in this investigation. Variables are factors which will have an effect on the results of the experiment. It is important to keep most of the variables constant or "controlled", they do not change, to ensure a fair test. The controlled variables are: the height of the calorimeter above the spirit burner, the material of the calorimeter, the change in temperature, the amount of water, the size of the copper calorimeter and the size of the wick, which was easily chosen as only one size was available. The rise in temperature was decided to be a 15�C increase from the difference of the initial and final temperature, because it did not ...read more.

Middle

8 � O- -C: 8 � 805 = 6440 10 � O-H: 10 � 464 = 4640 Total: - 11080 kJ/mole ?H = + 8559 - 11080 = - 2521 kJ/mole Pentanol Equation: Structure: Bonds Breaking (+) 11 � C-H: 11 � 412 = 4532 4 � C-C: 4 � 347 = 1388 1 � C-O: 1 � 358 = 358 1 � O-H: 1 � 464 = 464 7.5 � O=O: 7.5 � 498 = 3735 Total: + 10477 kJ/mole Bonds Making (-) 10 � O=C: 10 � 805 = 8050 12 � O-H: 12 � 464 = 5568 Total: - 13618 kJ/mole ?H = + 10477 - 13618 = - 3141 kJ/mole CH4O (l) + 1.5O2 (g) CO2 (g) + 2H2O (l) C2H6O (l) + 3O2 (g) 2CO2 (g) + 3H2O (l) C3H8O (l) + 4.5O2 (g) 3CO2 (g) + 4H2O (l) C4H10O (l) + 6O2 (g) 4CO2 (g) + 5H2O (l) C5H12O (l) + 7.5O2 (g) 5CO2 (g) + 6H2O (l) When I group all the equations together a pattern emerges: Every time n increases by 1. In the alcohol molecule, H increases by 2n. the number of; O2 molecules increases by 1.5, CO2 increases by 1 and H2O molecules increase by 1. therefore the general formula of this equation is : CnH2n+1OH + 1.5nO2 nCO2 + (n+1)H2O I have already discussed what I will do after the experiment, and now I will be doing that. I will work out the energy released per mole, also known as enthalpy change (?H). I have just worked out the enthalpy change for each alcohol I will be using, by scientific methods. Therefore I predict the energies released per mole for the different alcohols to be similar to the results shown in the table below. Pentanol will give off more heat than methanol and I predict that less pentanol will need to react to raise the temperature of the water than methanol. ...read more.

Conclusion

However, the length of the wick did vary sometimes, a centimetre at most; this did affect the results though. To improve the experiment the wicks should all be the same length to make sure of a fair test. The distance between the calorimeter and the flame should be constant at 2cm for example. Draught shields (excluders) could be put up to reduce draught and insulate the heat loss escaping into the environment. The experiment could take place in a fume cupboard to minimize the heat loss. But the only realistic method could be the draught excluders. Further work could include using more alcohols and more repeats of them this would give clear evidence and increase the reliability of the results. I would say that the evidence is strong enough to draw conclusions from, because three repeats were just enough to maintain a strong average. My graph shows that the numbers of carbon atoms are directly proportional to the enthalpy change. This shows that the more carbon atoms the higher the level of enthalpy change. Overall my experiment was quite reliable considering all the sources of error. My prediction was not close to the results, the graph displayed the line of best fit was close to all the points so there was not a wider scatter of results. Except for my anomalies all the repeats were very close. This indicates that the results are reliable. Although the anomalies suggest they were not entirely reliable. If this experiment was to be done again, then all the possible sources of error mentioned would have to be counteracted and controlled, as well as using a wider range alcohols. I would also take more repeats so that a much more accurate average could be taken and the results would be more accurate and reliable. I suggest 6 or 7 repeats for each alcohol. More results would make a far conclusive and reliable and accurate. More repeats would show that the trend line stays the same and that the enthalpy change is directly proportional to the number of carbons atoms present. ?? ?? ?? ?? 1 ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Organic Chemistry section.

Found what you're looking for?

• Start learning 29% faster today
• 150,000+ documents available
• Just £6.99 a month

Not the one? Search for your essay title...
• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month

Related GCSE Organic Chemistry essays

1.  Experiment to investigate the heat of combustion of alcohols.

4 star(s)

carbon atoms and the heat of combustion is linear, therefore producing a line of best fit, going through the origin for all the graphs. This means that the heat of combustion (kJ/mol) is proportional to the size of the alcohol molecule (number of carbon atoms increases as the alcohol molecule becomes longer).

2. Investigating the Combustion of Alcohols

Temperature rise Inaccuracy 5�C 20% 10�C 10% 25�C 4% 50�C 2% Our group decided to use a 25�C temperature rise. Reason being, that its inaccuracy percentage is low compared to the rest and a 50�C rise would prolong the experiment even further as it would take a long time to achieve the required temperature.

1. Esters. Esters are formed from an alcohol and carboxylic acid; this is an ...

At present, cosmetics testing is generally faring well without the use of animal testing in areas where it is banned and this trend might continue to take hold of other countries. The practice is particularly controversial because animals may experience discomfort, suffering and ultimately die, all in the name of aesthetics and 'looking good.'

2. Comparing the Enthalpy Changes of Combustion of Different Alcohols

burner which means that combustion will not be steady and possibly at times not complete either (where combustion is complete it is standard ?Hc). Incomplete combustion is where a lack of oxygen (O2) is present during combustion and so carbon monoxide (CO)

1. Comparing the enthalpy changes of combustion of different alcohols.

As I am using data books for the enthalpy change of combustion it will be an insufficient use of my time to calculate the value using this method for all of the alcohols that I plan to use. Data obtained from Data sheets from Salters Advanced chemistry 2000, Table 20

2. This project was set out to test the strength of different carbon chains in ...

is from flame Temperature change of water I decided that 5 alcohols was sufficient if I repeated each alcohol 3 times to make sure that the results were accurate. I am going to burn 5 types of alcohol. The alcohol will heat a flask of water with a set temperature rise.

1. Comparing the enthalpy changes of combustion of different alcohols

Methanol, Propan-1-ol and Butan-1-ol can all cause irreversible effects and seriously harm skin, eyes and can cause drowsiness, dizziness and is very harmful if swallowed. This is why I will be wearing goggles and taking extra precautions when handling these harmful alcohols.

2. GCSE Chemistry Revision Notes - everything!

Bigger molecules become less flammable. This is because the ratio of carbon to hydrogen increases and more oxygen is needed for the molecule to burn. 3-dimensional formula H C H H H Hydrocarbons are often drawn using 3-D formula. • Over 160,000 pieces
of student written work
• Annotated by
experienced teachers
• Ideas and feedback to 