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Name______Section ______
LastFirst
CHEM 307.001/002 Dr. Amah
First Lab Examination60 minutes, 60 points maximum.
- (Credit 18) Please answer each of the following questions.
(a)Which of the following techniques (A-F) are best used to accomplish the following? Place the correct letter of the technique in the space provided by each statement. There is only one correct answer to each statement. Letters may be used more than once or not at all.
_____1. to separate a mixture of two organic liquidsA. filtration
______2. to purify a solid organic compoundB. gas chromatography
______3. to determine the percentages of two liquids in a mixtureC. recrystallization
______4. to determine the identity of a solid unknown, givenD. distillation
solid standards
______5. to separate a pure solid suspended in a liquidE. mixed melting point
______6. to determine the purity of a solid compoundF. melting point
(b)In a distillation, boiling chips are used to: (circle answer): raise, lower or do not affect the boiling point of a liquid.
(c)Name the piece of glassware that you used in lab to:
(1)separate an organic liquid from an aqueous layer ______
(2)dissolve the solid in recrystallizing a solid compound______
(d)A student did not preheat the glass funnel when doing a hot gravity filtration. What effect, if any, does this have on the amount of organic solid ultimately recovered?
- (Credit 14) Please answer each part.
(a)A prime consideration for recrystallization solvent is that the desired compound:
(1)should be soluble in the solvent when it is (circle answer) hot, cold, or at room temperature.
(2)should be insoluble in the solvent when it is (circle answer) hot or cold.
(b)An unknown compound A and three known compounds (R,S,T) all exhibit a melting point range 98-990C. On the basis of the following information, A is likely to be the same as which of the compound (R,S,T)? Answer ______
Mixture(50:50)Melting point range (0C)
A+R67-72
R+S72-78
R+T69-79
A+S97-98
A+T59-70
S+T89-95
(c)Simple distillation is easier to perform than fractional distillation. With this in mind, which type of distillation, simple or fractional, would be preferred for each of these separations?
(1)removing water from an aqueous solution inorganic salts such as NaCl.
(2)removing diethyl ether (bp 350C ) from a solution containing ether and dichlorobenzene (bp 1740C).
(3)separating a mixture of pentane (bp 360C) from cyclopentane (bp 490C) to obtain each in pure form.
(d)Which type of distillation column-packed or unpacked- provides the better separation of a mixture of two liquids? (Circle your choice).
(e)Beside each statement about fractional distillation, circle the best answer for the statement.
(1)the column contains no packing: good separation, bad separation, no effect.
(2)mixture is heated too rapidly: good separation, bad separation, no effect.
(3)mixture is heated slowly: good separation, bad separation, no effect.
4. (Credit 12) In the presence of H2SO4 as a catalyst, diethyl ether (MW 74 g/mol) may be prepared from ethanol (MW 46 g/mol) by the equation:
2CH3CH2OH→CH3CH2OCH2CH3 + H2O
ethanoldiethyl ether
If 7.4 g of ethanol was used and 2.1 g of diethyl ether was obtained in pure form:
(a)calculate the theoretical yield of diethyl ether in g. Please show your work.
(b)Calculate the percent yield of diethyl ether in this reaction. Please show your work.
5. (Credit 2) These questions pertain to the preparation of dulcin.
(a)At one point in the purification scheme, powdered charcoal was added to the solution of dulcin and allowed to boil. What was the purpose of doing this, and what did it remove?
(b)What solvent was used to recrystallize dulcin?
6. (Credit 8) Complete the following flow diagram for the separation of benzoic acid and naphthalene using dichloromethane as solvent by showing what is present in each box.