Owl Questions Flashcards
The melting point of a sample of compound X was found to be 156-160. Compound X was one of four possible compounds having melting points of 156, 158, 160, and 162. Which is it most likely to be?
162
In this lab a melting range of … indicates that a compound is relatively pure
2
In melting point determination, the heating rate as the solid is melting should be … per minute
1
If a second melting point determination must be taken for a sample. It is necessary to use a fresh sample and not the one that has already been used. Why?
The sample may have decomposed slightly.
Melting points can provide what type of information about a sample?
The identity and purity
A solid sample melted at 177-181. The compound was one of four possibilities. Which is it most likely to be?
- 183.5
- 177
- 181
- 179
183.5
Thin layer chromatography can be used to help determine what?
The purity of a compound, the number of components in a mixture, the identity of a compound
What are the three basic steps in TLC in the order which they are done.
Spotting, development, visualization
A TLC analysis was run on an unknown mixture. After visualization by two methods, three spots were observed. What can be concluded?
There are at least three components in the mixture
In a TLC analysis if the Rf’s of the spots are too small, then?
A development solvent of higher polarity should be used
In a TLC analysis, if the solvent was observed to travel 10cm and the spot was observed to travel 6.2cm, what is the Rf for that spot?
0.620
The three general types of impurities that may contaminate a solid sample are?
Soluble impurities, insoluble impurities, and colored impurities
Two obvious structural features that may affect the solubility of a compound are?
It’s ability to form hydrogen bonds and its polarity
The following compound would be expected to be most soluble in which of the following solvents:
CH3–CH3–CH3-CH3–CH3–CH3–CH3–CH3–CH3–OH
Hexane
The following molecule would be most soluble in which of the following solvents?
CH3–OH—O—CH3–OH—CH3–OH—CH3–OH—CH3–OH
Water
Solubility tests were carried out on an unknown solid and the following results were:
Water: high solubility cold, high solubility hot
Ethanol: high solubility cold, high solubility hot
Hexane: low solubility cold, low solubility hot
Toluene: low solubility cold, high solubility hot
Toluene
The correct amount of solvent to use in a recrystallization is?
The minimum needed to dissolve the solid near the solvents boiling point
What would be considered to be physical properties?
Solubility of caffeine in dichloromethane, melting point of cholesterol, boiling point of 2-methylnonane
What structural characteristic of thalidomide accounts for the fact that in one form it acts as a sedative and in another it acts as a teratogen?
Chirality
What would be considered chemical properties?
Acidity of 2-chlorobenzoic acid, rate of the SN2 reaction
In a TLC analysis, if the Rf of a compound was found to be too small, a … solvent having a … polarity should be chosen.
Developement, higher
Decaffeinating coffee or tea represents what type of extraction?
Solution into another solvent
When two liquids that are mostly insoluble in one another are mixed together, they separate into two layers. Whether one liquid is the upper or lower layer depends upon the?
Relative densities of the two liquids
A sample of naphthalene was mixed with water and test-butyl methyl ether. The naphthalene dissolved mostly in the … layer. The ether layer was the … layer.
Ether, upper
