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If There Is a Relationship Between the Number of Carbon Atoms In Several Different Alcohols and the Heat of Combustion of Those Alcohols.

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Planning Experimental Procedures Introduction In this experiment, I plan to discover if there is a relationship between the number of carbon atoms in several different alcohols and the heat of combustion of those alcohols. I would also like to discover the nature of the relationship(if there is one). For example: if the heat of combustion increases or decreases with the number of carbon atoms and by how much. Apparatus Retort stand, boss, clamp, tin can, water, six alcohols (methanol, ethanol, propanol, butanol, pentanol, hexanol.) in burners, Bunsen burner, heatproof mat, thermometer (0 - 100�c), digital scales. Method 1. Set up the retort stand as shown above. 2. Record the starting temperature of the water (100ml). 3. Take the first alcohol - in a burner - and weigh it on digital scales. Record the weight. 4. Light the wick on the burner and allow it to burn until the temperature of the water in the can has risen by 20�c. WEAR GOGGLES AS HEAT IS BEING USED! 5. Re-weigh the burner and record its new weight. 6. Calculate the change in weight since lighting. 7. Repeat steps 2 - 6 twice more. 8. Repeat steps 2 - 7 for each of the other alcohols. ...read more.


There are five such bonds in ethanol so you multiply 410 by five to get 2050 joules. You do these calculations for all the other types of bonds that make up ethanol, add them all together and you get 3270 joules. All of the other alcohols can be broken up in this way. Below is a table showing the energy required to break up the bonds in each alcohol. Type of Alcohol Energy required to break bonds(j) Methanol 2100 Ethanol 3270 Propanol 4440 Butanol 5610 Pentanol 6780 Hexanol 7950 As you can see a longer molecule is, the more energy it takes to break its bonds. I can come to predict that the longer the molecular structure in the alcohol the more energy it will take to break the bonds. I also predict that the increase in energy required will be proportional to the number of extra carbon atoms. With each new carbon atoms that you add to the chain, you also add two new hydrogen atoms. Apart from this, the chain remains unchanged. I therefore predict that the energy required to break the bonds will increase by 1170 joules for each new carbon atom. Obtaining Evidence Summary of Results (First Repeat) ...read more.


Radiation of heat out into the atmosphere. 3. The fact that the tin can gets hot. 4. The rubber clamp transferred heat way. 5. By incomplete combustion 6. The activation energy to get the alcohol burning. 7. The availability of alcohol for the wick to burn, if not enough then the wick would burn not the alcohol which would give an inaccurate result. 8. Evaporation of water so there will be less water to heat, making the water hotter. 9. The size of the wick. 10. Not all of the water was the same temperature. 11. The flame size changed due to the type of alcohol, hence it was a different distance away from the beaker each time. I could obtain a better picture of how the number of carbon atoms affects the heat of combustion in two ways. 1. I could extend my current experiment by testing other alcohols such as heptanol or octanol as well as by doing more repeats to increase the accuracy of my results. 2. I could conduct a similar experiment with other homologous series of hydrocarbons such as the alkanes or the alkenes. This would allow me to compare the results from each experiment and compare how the number of carbon atoms in the chain affects the heat of combustion. ...read more.

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