5 Steps to a 5 AP Chemistry

Organic Chemistry  275

 Answers and Explanations

1. Cycloalkanes are hydrocarbons with the general
   formula CnH 2 n. If a 0.500 g sample of any alkene
   is combusted in excess oxygen, how many moles
   of water will form?
   (A) 0.50
   (B) 0.072
   (C) 0.036
   (D) 1.0
   (E) 0.018

2.

The organic compound shown above would be

classified as

(A) an organic base

(B) an ether

(C) an alcohol

(D) an aldehyde

(E) a ketone

3. Which of the following compounds is optically
   active?
   (A) CH 3 CHClCH 2 CH 2 CH 3
   (B) CH 3 CH=CHCH 2 CH 3
   (C) CH 3 CH 2 CHClCH 2 CH 3
   (D) CH 3 CH 2 CH 2 CH 2 OH
   (E) CH 3 CH 2 CH 2 CH 2 CH 3


4. A carboxylic acid may be represented as:
   (A) ROH
   (B) RCHO
   (C) R-O-R′
   (D) RCOOH
   (E) RCOOR′

O–H

|

CH 3 –CH–CH 2 –CH 3

 Review Questions

You have 5 minutes. You may not use a calculator. You may use the periodic table at the

back of the book. For each question, circle the letter of your choice.

1. C—The general formula, CnH 2 n, means that
   1 mol of H 2 O will form per mole of empirical
   formula unit, regardless of the value of n. The
   moles of water formed is the mass of the alkene
   divided by the empirical formula mass.

(0.500 g alkene)(l mol alkene/14 g alkene)(l mol

H 2 O/mol alkene)

=0.036 mol

2. C—Organic bases are, in general, amines
   (contain N). An ether would have an oxygen
   single-bonded to two carbons (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. Ketones

have oxygen double-bonded to a carbon not at

the end of a chain.

3. A—Redrawing the structures may help you to
   recognize the correct answer. An optical isomer
   must be a carbon atom with four differentgroups
   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 similar to A, but two
   of the groups, the −CH 2 CH 3 groups, are the
   same.


4. D—A=alcohol B =aldehyde C =ether E =ester