• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month
  1. 1
  2. 2
  3. 3
  4. 4
  5. 5
  6. 6
  7. 7
  8. 8
  9. 9
  10. 10
  11. 11
  12. 12
  13. 13
  14. 14

I am going to investigate how and why the enthalpy change is affected by the molecular structure of the alcohols under conditions, which I have stated under 'Plan' below.

Extracts from this document...


Comparing the enthalpy changes of combustion of different alcohols Introduction I am going to investigate how and why the enthalpy change is affected by the molecular structure of the alcohols under conditions, which I have stated under 'Plan' below. Sources I have used the following sources in aid of devising my plan: * My lecture notes. * Salters Advanced Chemistry: Chemical Storylines * 'Enthalpy' coursework form www.essaybank.co.uk Equipment I will use the following equipment: * Copper calorimeter * Thermometer * Stand * Boss * Clamp * 200 cm� measuring cylinder * Electronic balance * Bunsen burner * 2 Mats * 5 Splinters The above equipment are needed because the stand, boss and clamp will support and hold the metal calorimeter containing 200cm� water, which it will be heated up by the burning alcohol underneath. The thermometer is used to measure temperature before and after the experiment and the electronic balance is used to weigh the alcohol before and after the experiment. Two mats will be used to keep heat loss, by heating the environment, to a minimum The Bunsen burner is used to light the splinter, which in turn will set alight the alcohol. Water level will be the same for each of the alcohols combusted. All of procedures are to be carried out just to make the experiment fair. Materials Only the following straight-chained alcohols will be used: * Methanol(l) CH3OH * Ethanol(l) CH3CH2OH * Propan-1-ol(l) CH3CH2CH2OH * Butan-1-ol(l) CH3(CH2)2CH2OH * Propan-2-ol(l) CH3CH(OH)CH3 These alcohols are chosen because a wide range of alcohols are needed to be compared, as an aid to decide which alcohol releases the most energy when burned. It will also provide reliable data, showing the exact enthalpy change of combustion of each of the alcohols, which will be used during the experiment. Safety The following safety aspects need to be considered, in order to conduct experiments as safely as possible: * Follow instructions exactly. ...read more.


11. While the alcohol is burning, stir the water by using the thermometer from time to time. 12. Keep on heating the water inside the copper calorimeter until the temperature rises 20�C above the recorded temperature before the test. 13. Extinguish the burning alcohol. 14. Record the temperature after the test, before it decreases. 15. Weigh the methanol after the test and record the mass. 16. Pour the water into the sink. 17. Repeat procedures 2 to 15 for the rest of the alcohols, as stated above under 'Materials'. Remember to keep the conditions for the other alcohols the same as the first alcohol, in order to make the test fair. 18. Repeat the experiment again to cancel out any anomalies. Implementing Results Combustion of different alcohols by mass Experiment Alcohol Temperature (�C) ?T (�C) Mass (g) Mass Burnt (g) Initial Final Before After 1 Methanol 22 42 20 137.657 136.365 1.292 Ethanol 22 42 20 153.423 152.423 1 Propan-1-ol 22 42 20 148.643 147.828 0.815 Propan-2-ol 22 42 20 123.424 122.606 0.818 Butan-1-ol 22 42 20 148.896 147.838 1.058 2 Methanol 17 37 20 121.475 120.264 1.211 Ethanol 17 37 20 140.541 139.606 0.935 Propan-1-ol 22 42 20 130.724 129.678 1.046 Propan-2-ol 22 42 20 147.838 147.329 0.509* Butan-1-ol 18 38 20 143.363 142.538 0.825 Table 1 *Anomaly Water level: 200cm� ?T: 20� Analyse I have used the following formulas to calculate the values of enthalpies of combustion for all the alcohols I used during the experiment: Average enthalpy change of combustion Methanol 1. Use the Periodic Table to calculate the molecular mass of methanol. Write the mass number of each element stated in the molecular formula. If you see a number or the symbol of an element appears more than once, write the appropriate number and the mass number in brackets. Then multiply the sum in brackets first then add up the whole sum to obtain the molecular mass number, e.g.: * Mr(CH3OH) ...read more.


* Methanol: -430.77 kJ mol�� * Ethanol: -680 kJ mol�� * Propan-1-ol: -1050 kJ mol�� * Propan-2-ol: -1527.28 kJ mol�� * Butan-1-ol: -1292.31 kJ mol�� The percentage error values suggest that my results, concerning the average enthalpy change of combustion, were unreliable. This is because when I put each alcohol on the electronic scale, the values tend to move up and down, making measurement of the mass of each alcohol difficult. There are also limitations when using a thermometer and a measuring cylinder because I had to record the mass or temperature to the nearest gram or degree. I conducted the experiment in different conditions at 20�C (293K) and 1 atm. Then the temperature has decreased to 18�C (291K) during the experiment. I also manipulated the results by rounding it up or down, so this accounts about 5% of the error percentages. The main causes of anomalous results are heat loss by heating the environment, due to poor insulation of the copper calorimeter, soot on the bottom of the copper calorimeter, incomplete combustion, tiny amounts of water has been lost when pouring from the measuring cylinder into the copper calorimeter, impurities in the water and the experiment was not conducted under standard conditions; at 25�C (298K), 1 atm and using 1 mol dm�� of each alcohol. Improvements can be made to the procedure by: * Using the same burner * Keep the copper calorimeter at the same height * Pump enriched oxygen to the burner * Insulate the copper calorimeter. These procedures will ensure that the results obtained are accurate and reliable because if the same burner is used, the same amount of fuel would be burned since the length of the wick is the same. Keeping the copper calorimeter at the same height, means that the fire can reach the copper calorimeter from the burner at the same time. Pumping enriched oxygen would make combustion of the alcohols complete, so soot is not deposited on the bottom of the copper calorimeter. Finally, insulating the copper calorimeter prevents heat loss by heating the environment. Martin Yau Exam No. 6079 Centre No. 58231 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

See related essaysSee related essays

Related GCSE Organic Chemistry essays

  1. Marked by a teacher

    Experiment to investigate the heat of combustion of alcohols.

    4 star(s)

    indicates that you will need 412 joules to break a Carbon - Hydrogen bond. I have calculated the energy change for each alcohol, using the bond energies already given above: Methanol CH3 OH + 1.5O2 CO2 + 2H2O Bond Breaking Bond Making 3 (C - H)

  2. Investigating the Combustion of Alcohols

    Energy Values: - Extracted from the Nuffield Book of Data Broken kJ/mol C-H 413 O-H 464 O=O 498 C-C 347 C-O 358 Made kJ/mol C=O -805 O-H -464 Below is an illustration showing which bonds are broken and which bonds are made when methanol undergoes combustion.

  1. Titration experiment - write up

    The burette is first washed out with the solution it is to contain, the washings being allowed to run through the jet so as to wash this part also. A second washing is desirable to ensure complete elimination of impurities.

  2. To measure and compare the enthalpy change of combustion for four different types of ...

    Hazards Each fuel has different hazards, which need to be identified. Using the Major hazard card (Cleapss 1995) it is possible to identify these hazards. Methanol and Ethanol (Hazard card number 40) are highly flammable and will catch fire at temperatures above 13oC and they are dangerous with bromine, mercury and silver nitrate, platinum and potassium.

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

    - 2C - 3C - 4C - H | | | | OH H H H Butan-2-ol H H H H | | | | H - 1C - 2C - 3C - 4C - H | | | | H OH H H Pentan-1-ol H H H H H

  2. The Combustion of Alcohols and the factors affecting these reactions

    O-H: 1 � 464 = 464 Total: + 4473 kJ/mole Bonds Making (-) 2 � C=O: 2 � 805 = 1610 4 � O-H: 4 � 464 = 1856 Total: - 3466 kJ/mole ?H = + 3269 - 3466 = - 1007 kJ/mole Ethanol Equation: Structure: Bonds Breaking (+)

  1. Comparing the Enthalpy Changes of Combustion of Different Alcohols

    Although quite good given the apparatus available will not be able to achieve accurate results. This is because there are so many factors involved that I do not have control over. For instance in my experiment I cannot ensure a constant supply of oxygen to the flame of the spirit

  2. GCSE Chemistry Revision Notes - everything!

    Graphite is also a form of pure carbon, but it has a layer structure. In each layer the carbon atoms are also bound covalently, which means that the bonds within the layers are very strong, but the bonds between the layers of graphite are very weak, which enables layers to slide over one another.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work