CHM2211L FINAL EXAM UF
QUESTIONS AND ANSWERS WITH
CORRECT SOLUTIONS
Explain the purpose of the hot gravity filtration. Why is it good to use the stemless
funnel for this technique? - CORRECT ANSWES -- - Hot gravity filtration serves to
remove any insoluble impurities that do not dissolve when the solution is brought to its
boiling point.
- it is good to use the stemless funnel for this technique because this would minimize
any contact between the hot solution and the funnel. If a funnel with stem is used the
droplets of hot solution might get stuck on the stem inner surface and early
crystallization of the solution might occur
ligroin - CORRECT ANSWES -- solvent derived from petroleum consisting of C7 and
C8 hydrocarbon, non polar
Amide synthesis of acetophenetidin - CORRECT ANSWES -- p-phenetidine + acetic
anhydride (solvent: Sodium acetate and hydrochloric acid)
Why is the sample of p-phenetidine reddish brown? - CORRECT ANSWES -- small
amount of impurities caused by air oxidation of the amino functional group
how to remove reddish brown from p-phenetidine? - CORRECT ANSWES --
decolorizing carbon
Why should you not stir the crystals in the buchner funner? - CORRECT ANSWES --
this makes the filtration less efficient and does not adequately remove the solvent from
the crystal
Williamson Ether Synthesis - CORRECT ANSWES -- 1) p-acetamidophenol +sodium
methoxide, methanol, and ethanol
2) 1st product (addition of sodium) + Bromoethane
Why does the williamson ether synthesis take two steps? - CORRECT ANSWES --
Because the hydrogen on the alcohol group of acetamidophenol would react with the
bromoethane to create ethane and there would not be any reaction. The sodium acetate
turns that alcohol group into a nucleophile that would attack the C of the bromoethane
, Reflux condenser - CORRECT ANSWES -- Allows the reaction to be carried out at the
boiling point of the solvent and yet it prevents loss of solvent or reagent due to
evaporation. The vapors condense as they rise up the condenser and thus prevent
them from escaping.
What was the best recrystallization solvent for the acetophenetidin? - CORRECT
ANSWES -- Water because the solute is completely soluble at boiling point, but the
crystals reappear when solution is placed in an ice bath.
Melting Point - CORRECT ANSWES -- temperature at which the solid phase is in
equilibrium with the liquid phase
Pure Compound - CORRECT ANSWES -- sharp melting point, range is narrow (1-2
degrees)
Why does the presence of a soluble impurity in a sample has the effect of lowering and
broadening the melting point range? - CORRECT ANSWES -- because the impurity
disrupts the crystalline lattice of the sample so less energy is required to convert the
solid phase into a liquid phase
What effects does insoluble impurity like sand and glass has on MP? - CORRECT
ANSWES -- no effect
Errors of taking melting points: - CORRECT ANSWES -- 1. improper amount of sample
in capillary tube 2) mistaking sagging or shrinking sample as melting 3) presence of
solvent cause crystals to "sweat"
Benzoic acid - CORRECT ANSWES -- 122-123°C
Mandelic acid - CORRECT ANSWES -- 120-122°C
An unknown compound was determined to be 74.97% C, 8.39% H, and no nitrogen.
What is the empirical formula - CORRECT ANSWES -- 100-74.97-8.39 = 16.64% O
# of C: 74.97/12 = 6.25/1.04 = 6
# of H: 8.39/1=8.39/1.04= 8
# of O: 16.64/16 = 1.04/1.04 = 1
EmF: C6H8O
Can IR spectroscopy be used to distinguish 2-pentanone from 2-hexanone? why or why
not? - CORRECT ANSWES -- No because IR spectroscopy is used to distinguish
functional groups presents on molecules. Both 2-p and 2-h contains the same functional
group.
Acetophenetidin - CORRECT ANSWES -- analgesic and antipyretic (pain and fever
relief)
QUESTIONS AND ANSWERS WITH
CORRECT SOLUTIONS
Explain the purpose of the hot gravity filtration. Why is it good to use the stemless
funnel for this technique? - CORRECT ANSWES -- - Hot gravity filtration serves to
remove any insoluble impurities that do not dissolve when the solution is brought to its
boiling point.
- it is good to use the stemless funnel for this technique because this would minimize
any contact between the hot solution and the funnel. If a funnel with stem is used the
droplets of hot solution might get stuck on the stem inner surface and early
crystallization of the solution might occur
ligroin - CORRECT ANSWES -- solvent derived from petroleum consisting of C7 and
C8 hydrocarbon, non polar
Amide synthesis of acetophenetidin - CORRECT ANSWES -- p-phenetidine + acetic
anhydride (solvent: Sodium acetate and hydrochloric acid)
Why is the sample of p-phenetidine reddish brown? - CORRECT ANSWES -- small
amount of impurities caused by air oxidation of the amino functional group
how to remove reddish brown from p-phenetidine? - CORRECT ANSWES --
decolorizing carbon
Why should you not stir the crystals in the buchner funner? - CORRECT ANSWES --
this makes the filtration less efficient and does not adequately remove the solvent from
the crystal
Williamson Ether Synthesis - CORRECT ANSWES -- 1) p-acetamidophenol +sodium
methoxide, methanol, and ethanol
2) 1st product (addition of sodium) + Bromoethane
Why does the williamson ether synthesis take two steps? - CORRECT ANSWES --
Because the hydrogen on the alcohol group of acetamidophenol would react with the
bromoethane to create ethane and there would not be any reaction. The sodium acetate
turns that alcohol group into a nucleophile that would attack the C of the bromoethane
, Reflux condenser - CORRECT ANSWES -- Allows the reaction to be carried out at the
boiling point of the solvent and yet it prevents loss of solvent or reagent due to
evaporation. The vapors condense as they rise up the condenser and thus prevent
them from escaping.
What was the best recrystallization solvent for the acetophenetidin? - CORRECT
ANSWES -- Water because the solute is completely soluble at boiling point, but the
crystals reappear when solution is placed in an ice bath.
Melting Point - CORRECT ANSWES -- temperature at which the solid phase is in
equilibrium with the liquid phase
Pure Compound - CORRECT ANSWES -- sharp melting point, range is narrow (1-2
degrees)
Why does the presence of a soluble impurity in a sample has the effect of lowering and
broadening the melting point range? - CORRECT ANSWES -- because the impurity
disrupts the crystalline lattice of the sample so less energy is required to convert the
solid phase into a liquid phase
What effects does insoluble impurity like sand and glass has on MP? - CORRECT
ANSWES -- no effect
Errors of taking melting points: - CORRECT ANSWES -- 1. improper amount of sample
in capillary tube 2) mistaking sagging or shrinking sample as melting 3) presence of
solvent cause crystals to "sweat"
Benzoic acid - CORRECT ANSWES -- 122-123°C
Mandelic acid - CORRECT ANSWES -- 120-122°C
An unknown compound was determined to be 74.97% C, 8.39% H, and no nitrogen.
What is the empirical formula - CORRECT ANSWES -- 100-74.97-8.39 = 16.64% O
# of C: 74.97/12 = 6.25/1.04 = 6
# of H: 8.39/1=8.39/1.04= 8
# of O: 16.64/16 = 1.04/1.04 = 1
EmF: C6H8O
Can IR spectroscopy be used to distinguish 2-pentanone from 2-hexanone? why or why
not? - CORRECT ANSWES -- No because IR spectroscopy is used to distinguish
functional groups presents on molecules. Both 2-p and 2-h contains the same functional
group.
Acetophenetidin - CORRECT ANSWES -- analgesic and antipyretic (pain and fever
relief)
