1. A student who was performing a distillation for the firsttime failed to posit

Question

1. A student who was performing a distillation for the firsttime failed to position the thermometer correctly. The bulb was settoo high. What effect would this have on the observed boiling pointof the liquid being distilled?


2. Under perfect conditions, the number of theoretical platesrequired to separate an ideal mixture of two components of boilingpoints TA and TB is given by the relationship: Number of theoretical plates needed = 120 /TA - TB On this basis, how many theoretical plates are needed toseparate a mixture of cyclohexane and toluene? (Note: In practice,the actual number of theoretical plates required may be as high asdouble the number predicted by this equation!)

3. You suddenly notice you have forgotten to add boilingstones to your round bottomed distillation flask but thedistillation is now in progress. What should you do? 1. A student who was performing a distillation for the firsttime failed to position the thermometer correctly. The bulb was settoo high. What effect would this have on the observed boiling pointof the liquid being distilled?


2. Under perfect conditions, the number of theoretical platesrequired to separate an ideal mixture of two components of boilingpoints TA and TB is given by the relationship: Number of theoretical plates needed = 120 /TA - TB On this basis, how many theoretical plates are needed toseparate a mixture of cyclohexane and toluene? (Note: In practice,the actual number of theoretical plates required may be as high asdouble the number predicted by this equation!)

3. You suddenly notice you have forgotten to add boilingstones to your round bottomed distillation flask but thedistillation is now in progress. What should you do?

Explanation / Answer

1. The temperature observed as the solution begins to boil would belower than the actual boiling point because the thermometer ispositioned too high. 2. BP toluene = 110.6 C BP cyclohexane = 80.74 C Number of theoretical plates needed = 120/(110.6 - 80.74) =4.02 3. You could either stop and add the boiling stones or a boilingstick or you could scratch the bottom of the flask the solution isin to give a nucleation point for bubbles to form. There areactually a number of things you could do to fix the problemdepending on the setup. Hope this helps. :-)

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