CHEM 232 Final Exam with 100%
Correct Answers
Consider the structure of the impure compound to be recrystallized. Is the compound....
- ANSWER-has some polar features
What type of solvent would be appropriate for recrystallization of this compound? -
ANSWER-polar
Rank the solvents in order of increasing polarity - ANSWER-hexane
acetone
ethanol
water
Solubility of ethanol - ANSWER-soluble at high temperatures
insoluble at low temperatures
impurity - ANSWER-recovery less than 100%
Which solvent would you use for recrystallizing (2 carboxylic acids and 3 benzene) -
ANSWER-This compound is slightly polar so ethanol should be used
Water = too polar
Gravity Filtration - ANSWER-used when the product of interest is in the filtrate
Vacuum filtration - ANSWER-leaves behind impurities
lower boiling point than literature - ANSWER-indicates presence of impurities
2-naphthol - ANSWER-weak acid
Which reagent will convert 2-naphthol into an ionic compound - ANSWER-a strong base
3-Nitrobenzoic acid - ANSWER-strong acid
Which reagent will convert 3-nitrobenzoic acid into a ionic compound - ANSWER-a
weak base
1,4-dimethoxybenzene - ANSWER-neutral
, Which reagent will convert 1,4-dimethoxybenzene into an ionic compound - ANSWER-
none; neutral
Which compound would be present in the aqueous layer after extraction with sodium
bicarbonate? - ANSWER-3-nitrobenzoic acid
Which compound would be present in the aqueous layer after extraction with sodium
hydroxide? - ANSWER-2-naphthol
Which compound would be present in the ether layer after 2 extractions? - ANSWER-
1,4-dimethoxybenzene
Could we have performed the extraction experiment using acetone as the solvent
instead of diethyl ether as instructed in the procedure? - ANSWER-No. Acetone is
miscible in water so it would not be possible to tell the difference between the aqueous
and organic layer
Supposed you were asked to separate acetanilide and 1,4-dimethoxybenzene using
liquid-liquid extraction if the two compounds were dissolved in dichloromethane. Using
HCl, or NaOH or NaHCO3, would you be able to separate the two solids? - ANSWER-
No bc they are both neutral compounds
The stationary phase is.... (TLC) - ANSWER-polar
The mobile phase is... (TLC) - ANSWER-slightly polar
Chlorophyll-a - ANSWER-blue pigment
slightly polar
Chlorophyll-b - ANSWER-greenish yellow pigment
slightly polar
Xanthophyll - ANSWER-yellow pigment
polar
carotene - ANSWER-orangish yellow pigment
non polar
order of pigments on TLC plate (least to greatest distance traveled - ANSWER-
xanthophyll
chlorophyll-b
chlorophyll
carotene
Correct Answers
Consider the structure of the impure compound to be recrystallized. Is the compound....
- ANSWER-has some polar features
What type of solvent would be appropriate for recrystallization of this compound? -
ANSWER-polar
Rank the solvents in order of increasing polarity - ANSWER-hexane
acetone
ethanol
water
Solubility of ethanol - ANSWER-soluble at high temperatures
insoluble at low temperatures
impurity - ANSWER-recovery less than 100%
Which solvent would you use for recrystallizing (2 carboxylic acids and 3 benzene) -
ANSWER-This compound is slightly polar so ethanol should be used
Water = too polar
Gravity Filtration - ANSWER-used when the product of interest is in the filtrate
Vacuum filtration - ANSWER-leaves behind impurities
lower boiling point than literature - ANSWER-indicates presence of impurities
2-naphthol - ANSWER-weak acid
Which reagent will convert 2-naphthol into an ionic compound - ANSWER-a strong base
3-Nitrobenzoic acid - ANSWER-strong acid
Which reagent will convert 3-nitrobenzoic acid into a ionic compound - ANSWER-a
weak base
1,4-dimethoxybenzene - ANSWER-neutral
, Which reagent will convert 1,4-dimethoxybenzene into an ionic compound - ANSWER-
none; neutral
Which compound would be present in the aqueous layer after extraction with sodium
bicarbonate? - ANSWER-3-nitrobenzoic acid
Which compound would be present in the aqueous layer after extraction with sodium
hydroxide? - ANSWER-2-naphthol
Which compound would be present in the ether layer after 2 extractions? - ANSWER-
1,4-dimethoxybenzene
Could we have performed the extraction experiment using acetone as the solvent
instead of diethyl ether as instructed in the procedure? - ANSWER-No. Acetone is
miscible in water so it would not be possible to tell the difference between the aqueous
and organic layer
Supposed you were asked to separate acetanilide and 1,4-dimethoxybenzene using
liquid-liquid extraction if the two compounds were dissolved in dichloromethane. Using
HCl, or NaOH or NaHCO3, would you be able to separate the two solids? - ANSWER-
No bc they are both neutral compounds
The stationary phase is.... (TLC) - ANSWER-polar
The mobile phase is... (TLC) - ANSWER-slightly polar
Chlorophyll-a - ANSWER-blue pigment
slightly polar
Chlorophyll-b - ANSWER-greenish yellow pigment
slightly polar
Xanthophyll - ANSWER-yellow pigment
polar
carotene - ANSWER-orangish yellow pigment
non polar
order of pigments on TLC plate (least to greatest distance traveled - ANSWER-
xanthophyll
chlorophyll-b
chlorophyll
carotene
