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Out the bond energies of the alcohols in the homologous series up to Pentanol, comparing them to the data book values.

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Introduction

Planning: Aim: To try to work out the bond energies of the alcohols in the homologous series up to Pentanol, comparing them to the data book values. There are a few factors in these experiments that will affect our enthalpies (as opposed to the data book values), which will be outlined later on in the write-up. Equipment: An alcohol burner - This is the heat provider. Heat proof mats - To insulate heat. A stand + clamps - To support the experiment structurally. A thermometer - To discern the starting and finishing temperatures. 50ml of water - Substance to be heated. A copper can - Metal conductor of heat. Electronic scales - To weigh the burners. A measuring cylinder - To measure out the correct volume of water accurately. Hypothesis: I predict that the enthalpies of the alcohols will decrease as the number of carbons increases. The results should reflect the text book values to some extent and show a correlation between each other with a steadily decreasing trend (in terms of the enthalpy). Factors: Here are some of the factors that could have affected our results in some way or other: * There was no proper draught insulation - We only had heat proof mats to insulate the heat and to stop it from heating the surrounding air rather than the can containing the water. * The distance from the heat source and the can itself differed for some experiments as we did these experiments over a period of 3-4 lessons. ...read more.

Middle

5. Make sure the can height is constant for each experiment. 6. Making sure that the lid of the alcohol burner is fixed on top of the burner (to stop the alcohol evaporating away), weigh the burner on a set of electronic scales - making sure the figures are accurate to 2 decimal places. Note down the starting mass of the alcohol burner. 7. Then, place 50ml of water into the copper can that is suspended directly above the alcohol burner. 8. Note down starting temperature. 9. Light the wick of the alcohol burner and quickly set up an insulation barrier of heatproof mats to block out any draughts or unnecessary heat loss. 10. When the temperature of the water has increased by 30�C, hastily blow out the flame that's burning merrily atop the alcohol burner (without spilling the alcohol burner as we managed to do once...) and immediately bung the lid onto the burner and reweigh the alcohol burner on the SAME set of electronic scales to the same degree of accuracy as before. 11. When all has been completed to a reasonable level of satisfaction, breathe a sigh of relief and brace oneself for the repeat of the whole procedure for the same alcohol (do each alcohol twice to validate results) and move up the homologous series steadily using the procedure outlined above to complete the experiment. Equations for the bond energy: Obtaining Evidence: Results: Kj/mol MRs Methanol -726 32 Ethanol -1367 46 Propan-1-ol -2021 60 Propan-2-ol -2006 60 Butanol -2676 Pentanol ...read more.

Conclusion

Also, since we had spread our experiments over several lessons, we hadn't paid much attention to the distance between the can and the alcohol burner so it varied over each lesson. Luckily, we did have some idea of how far away the alcohol burner was from the can so we adjusted it accordingly otherwise there might have been some serious consequences on our results... The lack of Butanol in the lab was a setback for us as we couldn't obtain the results we needed for that alcohol but since we tested each alcohol twice, it didn't really matter (that we didn't get to test Butanol) as we could guess pretty much where Butanol's enthalpy lay on our graph from the results we had obtained during our experiments. The fact that there were no proper draught insulating materials available to us so that we had to make to with using heat proof mats as the draught shields in our experiments was a potential error. Also, there weren't enough to go around so some experiments ended up having virtually no heat insulation and some experiments looking like crude igloos. Possible Improvements: We could all do with a bit more common sense here and there. Possibly our experiment may be executed quicker if we'd another go at it. The distance from the can to the alcohol burner should be logged and kept as similar as possible through the experiments. Some Butanol can be obtained for the next experiment as well because it may have helped... Purchasing some proper draught insulating and heat insulating material wouldn't go amiss either. ...read more.

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