Intermolecular forces
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Recently I have done several experiments, and I have following questions:
A: Equal volumes of ethanol and cyclohexane were mixed in a foam cup.
* Why should the foam cup be fitted in a beaker?
* Why is there a decrease in temperature?
* Is the mixing process exothermic?
B: To measure the strength of H-bond formed between ethanol molecules, as above but using 20 cm3 of cyclohexane.
* Why cyclohexane has to be used in excess in this experiment?
* Is it reliable of the H-bond strength obtained?
* As there are temperature drop of this experiment, then what is the hydrogen bond strength in ethanol, is it strong, and why?
C: To discover the formation of H-bond between molecules of ethyl ethanoate and trichloromethane equal volumes were mixed in an insulated beaker and the highest temperature measured.
* Why is an insulated beaker used instead of a polystyrene foam cup?
* Is the mixing process endothermic?
* Why is there are temperature change?
D: To estimate a value for the strength of hydrogen bond between ethyl ethanoate and trichloromethane, repeat steps (1) and (2) in part c above using either one liquid in excess.
* Why it does not matter which liquid is used in excess?
* There are temperature rise in this experiment, what is the strength of the hydrogen bond formed between ethyl ethanoate and trichloromethane. Is it strong, and why?
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Igloo writes ...
This is clearly a homework exercise. Consequently it would be wrong for me simply to give you all the answers. You say that you’ve carried these experiments, so there’s no point in my giving you answers to questions such as “Is the mixing process endothermic?”, since your own results will give you the answer!
I shall go through some of your questions and provide one or two answers together with some ideas as to how to carry out your own research from your text book or notes.
Section A
The foam cup tends to get knocked over quite easily, especially if there is a thermometer in it. Placing it in a beaker makes the arrangement more stable.
This mixing involves the breaking of very strong hydrogen bonds between ethanol molecules. What intermolecular firces are there between cyclohexane molecules and what intermolecular forces could theoretically arise between ethanol and cyclohexane? You must think this out for yourself, and then you should be able to answer the other questions.
Section B
An excess of cyclohexane ensures that as many of the hydrogen bonds in ethanol are being broken as possible.
Section C
Ethyl ethanoate dissolves polystyrene, so your cup would collapse! Therefore an insulated glass beaker is used instead.
Risk assessment
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For further guidance see our tutorial on Risk Assessment.
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updated: 14 April 2008
