278 ❯ STEP 4. Review the Knowledge You Need to Score High
CC NCH 3 HCH 3 CH 3CHHC CHHCC
H- The organic compound shown above would be
classified as:
(A) an organic base
(B) an ether
(C) an alcohol
(D) an aldehyde - A carboxylic acid may be represented as:
(A) ROH
(B) RCHO
(C) R–O–R′
(D) RCOOH- Which basic concept from the first half of the
textbook best explains why carbon in stable
organic compounds has four bonds?
(A) VSEPR
(B) octet rule
(C) Avogadro’s hypothesis
(D) electronegativity - Which of the following is the one reaction that
all organic compounds will undergo?
(A) neutralization
(B) precipitation
(C) combustion
(D) polymerization
❯ Answers and Explanations
- C—The general formula CnH2n means that
1 mole of H 2 O will form per mole of empirical
formula unit, regardless of the value of n. The
moles of water formed are the mass of the alkene
divided by the empirical formula mass:
(14 g alkene)
1 mol alkene
14 g alkene1 mol HO
1 mol alkene(^2)
= 1.0 mole
- C—Organic bases are, in general, amines (con-
tain N). An ether would have an oxygen atom
single-bonded to two carbon atoms (R groups).
An aldehyde has oxygen double-bonded to a
carbon at the end of a chain. Aldehydes (RCHO)
and alcohols (ROH) are often confused because
of the similarity in their general formulas; how-
ever, in alcohols, the hydrogen atom in the
general formula (ROH) is attached to an oxygen
atom, whereas in aldehydes, the hydrogen atom
in the general formula (RCHO) is attached to
a carbon atom. Ketones have oxygen double-
bonded to a carbon not at the end of a chain.
3. D—The combination of an OH group attached
to a carbon atom and an oxygen atom with a
double bond to the same carbon atom is charac-
teristic of a carboxylic acid.
4. A—Redrawing the structures may help you to
recognize the correct answer. An optical isomer
must be a carbon atom with four different groups
attached to it. For A, the groups on the second
carbon are CH 3 –, H, Cl, and –CH 2 CH 2 CH 3.
Answer C is misleading. It is like A, but two of
the groups, the –CH 2 CH 3 groups, are the same.
Many biologically important molecules are
optical isomers. - D—A is an alcohol, B is an aldehyde, and C is
an ether. - D—The highest pH is the result of dissolving a
base in water. A is an aldehyde, which is neutral.
B is an alcohol, which is neutral (or very slightly
acidic). C is a carboxylic acid, which is an acid.
D is an amine, which is a base.