CHM2211L Final Exam UF questions well answered-24.docx, Exams of
Advanced Education
Melting Point - ANSWERtemperature at which the solid phase is in
equilibrium with the liquid phase
Pure Compound - ANSWERsharp 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? - ANSWERbecause 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? -
ANSWERno effect
Errors of taking melting points: - ANSWER1. 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 - ANSWER122-123°C
,Mandelic acid - ANSWER120-122°C
An unknown compound was determined to be 74.97% C, 8.39% H, and no
nitrogen. What is the empirical formula - ANSWER100-74.97-8.39 = 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? - ANSWERNo because IR spectroscopy is used to distinguish
functional groups presents on molecules. Both 2-p and 2-h contains the same
functional group.
Acetophenetidin - ANSWERanalgesic and antipyretic (pain and fever relief)
p-acetamidophenol - ANSWERWilliamson ether synthesis
p-phenetidine - ANSWERAmide synthesis
Recrystallization - ANSWERsolvent that will completely dissolve both desired
compound and impurities when the solvent is hot; desire compound must be
insoluble in the chosen solved at cold temperature and inorganic remains
soluble when cooled
, What do seed crystals do? - ANSWERThey serve as nucleation sites where
more molecules of the desired compound deposit themselves in layers.
Explain the purpose of the hot gravity filtration. Why is it good to use the
stemless funnel for this technique? - ANSWER- 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 - ANSWERsolvent derived from petroleum consisting of C7 and C8
hydrocarbon, non polar
Amide synthesis of acetophenetidin - ANSWERp-phenetidine + acetic
anhydride (solvent: Sodium acetate and hydrochloric acid)
Why is the sample of p-phenetidine reddish brown? - ANSWERsmall amount
of impurities caused by air oxidation of the amino functional group
how to remove reddish brown from p-phenetidine? - ANSWERdecolorizing
carbon
Why should you not stir the crystals in the buchner funner? - ANSWERthis
makes the filtration less efficient and does not adequately remove the
solvent from the crystal
Advanced Education
Melting Point - ANSWERtemperature at which the solid phase is in
equilibrium with the liquid phase
Pure Compound - ANSWERsharp 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? - ANSWERbecause 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? -
ANSWERno effect
Errors of taking melting points: - ANSWER1. 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 - ANSWER122-123°C
,Mandelic acid - ANSWER120-122°C
An unknown compound was determined to be 74.97% C, 8.39% H, and no
nitrogen. What is the empirical formula - ANSWER100-74.97-8.39 = 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? - ANSWERNo because IR spectroscopy is used to distinguish
functional groups presents on molecules. Both 2-p and 2-h contains the same
functional group.
Acetophenetidin - ANSWERanalgesic and antipyretic (pain and fever relief)
p-acetamidophenol - ANSWERWilliamson ether synthesis
p-phenetidine - ANSWERAmide synthesis
Recrystallization - ANSWERsolvent that will completely dissolve both desired
compound and impurities when the solvent is hot; desire compound must be
insoluble in the chosen solved at cold temperature and inorganic remains
soluble when cooled
, What do seed crystals do? - ANSWERThey serve as nucleation sites where
more molecules of the desired compound deposit themselves in layers.
Explain the purpose of the hot gravity filtration. Why is it good to use the
stemless funnel for this technique? - ANSWER- 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 - ANSWERsolvent derived from petroleum consisting of C7 and C8
hydrocarbon, non polar
Amide synthesis of acetophenetidin - ANSWERp-phenetidine + acetic
anhydride (solvent: Sodium acetate and hydrochloric acid)
Why is the sample of p-phenetidine reddish brown? - ANSWERsmall amount
of impurities caused by air oxidation of the amino functional group
how to remove reddish brown from p-phenetidine? - ANSWERdecolorizing
carbon
Why should you not stir the crystals in the buchner funner? - ANSWERthis
makes the filtration less efficient and does not adequately remove the
solvent from the crystal
