5 Steps to a 5 AP Chemistry 2019

Organic Chemistry ❮ 279

7. A—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. The
   illustrated compound has no oxygen present;
   therefore, it cannot be an aldehyde or an alcohol.


8. D—The combination COOH represents an
   –OH group attached to a carbonyl group (C=O),
   which makes this a carboxylic acid. A is an alcohol

because there is an organic group attached to the

–OH. B is an aldehyde because there is a hydro-

gen atom attached to the carbonyl group. C is

an ether because there is an oxygen atom bonded

to two organic groups. (The generic term for an

organic group containing only C and H is R.)

9. B—A carbon atom, with four bonds, is sur-
   rounded by 4 × 2 = 8 electrons (an octet).


10. C—All organic compounds burn.

❯ Free-Response Questions

You have 20 minutes to answer the following questions. You may use a calculator and the

tables in the back of the book.

Question 1

The alkane hexane, C 6 H 14 , has a molecular mass of 86.17 g mol–1.

(a) Like all hydrocarbons, hexane will burn. Write a balanced chemical equation for the

complete combustion of hexane. This reaction produces gaseous carbon dioxide, CO 2 ,

and water vapor, H 2 O.

(b) The complete combustion of 10.0 g of hexane produces 487 kJ. What is the molar heat

of combustion (ΔH) of hexane?

(c) Determine the pressure exerted by the carbon dioxide formed when 5.00 g of hexane

is combusted. Assume the carbon dioxide is dry and stored in a 20.0 L container at

27 °C. Show all work.

(d) Hexane, like most alkanes, may exist in different isomeric forms. The structural formula

of one of these isomers is pictured below. Draw the structural formula of any two other

isomers of hexane. Make sure all carbon atoms and hydrogen atoms are shown.

HC

H

H

CCCCCH

H H H H H

H H H H H

Question 2

Amino acids are biological molecules with an organic acid group and an organic base

group present. These two groups react with each other. The simplest natural amino acid is

glycine, NH 2 CH 2 COOH, which, after its internal acid–base reaction, is better formulated

as [N+H 3 CH 2 COO-].