Lab Midterm Exam Q+A Flashcards
(14 cards)
What is the Chem 206L policy on food in the lab?
It is not permitted to eat or drunk in the lab at any time
Compound A has a melting point range of 85-87 C and Compound B has a melting point range of 87-89 C. An unknown Compound X is found to have a melting point range of 86-88 C. Compounds X and A are mixed together, and a mixed melting point analysis gives a range of 71-78 C. What does this indicate?
Compound X is not Compound A
True or false: for efficient recrystallization of an unknown compound, the compound must have high solubility in hot or boiling solvent
True
True or false: for efficient recrystallization of an unknown compound, the compound must have low solubility in hot or boiling solvent
False
True or false: for efficient recrystallization of an unknown compound, the compound must have high solubility in cold solvent
False
True or false: for efficient recrystallization of an unknown compound, the compound must have low solubility in cold solvent
True
Mescaline is a benzene ring with three OCH3 substituents and one ethane+primary amine substituent. If placed into a separatory funnel with 3M HCl(aq) and diethyl ether, which layer will it partition into?
The aqueous layer
Four compounds are isolated from anise and fennel: anisole, anisidine, anisic acid, and allylanisole. You have at your disposal diethyl ether, HCl(aq), and NaOH(aq). Which two of these compounds CANNOT be separated from each other using your given extraction tools?
Anisole and allylanisole
They are both nonpolar and unreactive to HCl and NaOH
How many total gauche interactions does the higher energy conformation of trans-1,2-dimethylcyclohexane have?
4
How do the C-C bond lengths in benzene and cyclohexane compare to each other?
Benzene C-C length < cyclohexane C-C length
What is usually the mobile phase in gas chromatography?
An inert gas, such as helium
How should a thermometer be placed in a distillation setup?
So that its bottom end rests by the exit pipe. The bottom end should not be in the round bottom flask with the liquid, nor should it be above the entrance mouth of the exit pipe
How do identify which compound has the lowest concentration in a mixture using a gas chromatograph?
The peak with the lowest area % corresponds to the compound with the lowest concentration in the mixture
You are given a gas chromatograph. The sample shown on the graph was a distillation fraction run with the same stationary phase we used in our lab. Compound B has a very short peak close to X=0 and Compound A has a very tall peak close to X=350. Compounds A and B have the same molecular weight. What can be determined from this chromatograph?
Compound A has a higher boiling point that Compound B
The sample is a late fraction from the distillation
