Practical investigations
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At present I am investigating the reaction between iodine and propanone with a concentrated hydrochloric acid catalyst. I have already found the orders of the reaction and now I would like to investigate the activation energy, but I cannot find a method anywhere. Do you have any suggestions? Thank you!
Igloo writes ...
You need to choose the conditions you used with one of your experiments, i.e. use a fixed concentration of iodine, propanone and concentrated hydrochloric acid in all these experiments. By preference, choose a set of conditions which gave a relatively slow rate of reaction.
Next, repeat this experiment over a range of temperatures, say 20 °C, 25 °C, 35 °C, etc. and measure the rate of reaction in each case. You don’t need to use these precise temperatures, of course, but space out the readings so that you cover temperatures in the range from room temperature up to about 40 °C, or perhaps 50 °C (higher temperatures than these cause iodine and, to a certain extent propanone, to volatilise away much more appreciably).
To carry out these experiments use some sort of water bath, perhaps a large beaker containing heated water. It is a good idea to measure out the volumes of solutions first, and warm them up in the water bath until a constant temperature in the required range is reached, before mixing them and “starting the clock”.
Finally you will need to make use of the Arrhenius equation to deduce the activation energy. This will involve a plot of log(rate) against the reciprocal of the temperature measured in Kelvin. I suggest you search the internet or use a standard A-level Chemistry text book to find out more about how to carry out the necessary calculations.
Always carry out a risk assessment and check with your teacher before starting any practical work.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 17 January 2006
