1* you use 25% ethyl acetate (an ester) in hexane to run a tlc and obtain a single round spot with an Rf of 0.9 for the main compound. what should you do?
A) try a completely different set of solvents, as ethyl acetate and hexanes will never work
B) try 10% ethyl acetate to see the results
C) try 35% ethyl acetate to see the results
D) assume that tic will be useless and find a different way to see id the sample is pure
E) conclude that the sample is pure
2. two compounds have the same calculated Rt under the same conditions. what can you conclude?
A) the two compounds can be concluded to be the same
B) only if they can be visualized by the same method can you conclude that they are the same compound
C) only if your run multiple tlc plates and get the same results can you conclude that they are are the same compound
D) identical Rt values, even when the two compounds are co-spoted , is some evidence that they are the same compound, but is insufficient by itself to confirm they are the same
E) only if you are using fresh tlc plates should you conclude the are the same
3. you are running a reaction to make a carboxylic acid. but what appears to be the product spot is too low on the tlc plate and is elongated , it isnt a nice circle but is stretched out a lot. to make this spot rounder and move a little farther, which of the following is most likely to work?
A) Using a more polar eluting solvent mixture
B) adding a trace of ammonium hydroxide to the eluting solvent mixture
C) adding a trace of methanol to the eluting solvent mixture
D) adding a trace of water to the eluting solvent mixture
E) adding a trace of acidic acid to the eluting solvent mixture