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CHEM 219 UNIT 5 EXAM WITH
CORRECT SOLUTIONS
Question : Generic formula for alcohols
CORRECT ANSWER : R-OH
Question : phenol
CORRECT ANSWER : hydroxy-substituted aromatic
molecules (any compound with an -OH attached to a benzene ring)
Question : IUPAC system rules for naming organic
alcohols
CORRECT ANSWER : - organic alcohols are named by
replacing the suffix of the parent chain of the molecule with the suffix -ol- The parent chain is numbered so as to give the hydroxyl group the lowest possible number.
(examples: 1-propanol, and cyclohexanol)- with
unsaturated alcohols the -ol suffix comes last and takes priority when numbering the parent chain (2-propene-1- ol)- Molecules with more than one -OH group get a prefix
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describing the number of -OH groups added to the IUPAC name. (ethane-1,2-diol)
Question : Molecules with more than one -OH group
CORRECT ANSWER : polyols
Question : IUPAC rules for phenols
CORRECT ANSWER : - the suffix for an alcohol
substituted benzene is "phenol"- start the numbering at
the OH group (so OH is at the 1 position)(examples:
phenol, 3-methylphenol, 2,4-dinitrophenol)
Question : Why can alcohols form strong hydrogen
bonds?
CORRECT ANSWER : Due to the presence of the
hydroxyl group, as the O-H bond is highly polarized by the electronegative oxygen atom. This polarization places a + charge on the hydrogen atom and a - charge on the oxygen atom. The polarization in the O-H bond on one alcohol molecule becomes attracted to the polarization in the O-H bond of another alcohol molecule.
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Question : Why do alcohols have much higher boiling
points than other molecules of similar molecular weight?
CORRECT ANSWER : hydrogen bonding between
alcohol moleculesThese attractions raise the amount of energy required to vaporize the liquid-phase molecules (boil), which translates into increased boiling point temperatures.
Question : Alcohol molecules can freely hydrogen bond
to other molecules possessing what groups?
CORRECT ANSWER : O-H, N-H, or S-H functional
groupings
Question : How does the water solubility of alcohol
molecules change as the molecular weight changes?
CORRECT ANSWER : Alcohol molecules of lower
molecular weight are mostly soluble in water as a result of the ability to hydrogen bond to OH, NH, or SH groups.As the molecular weight or carbon-chain length increases,
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the alcohol molecules become correspondingly less soluble in water.
Question : How do alcohols and phenols act as weak
acids and weak bases?
CORRECT ANSWER : - acts as an acid by donating the
O-H proton as H- acts as a base by accepting H+ using a lone pair on the O atom
Question : amphoteric substances
CORRECT ANSWER : Substances that can act as both
acids and bases (alcohols and phenols)
Question : Why is acid dissociation for most alcohols
unfavorable (lies towards the left)?
CORRECT ANSWER : Dissociation produces an
alkoxide ion (the conjugate base of an alcohol), which is a very strong base.