Video Transcript
Which of the following esters will
be obtained when methanoic acid reacts with methanol? (A) HCOOC2H5, (B) HCOOCH3, (C)
CH3CH2COOCH3, (D) CH3COOCH3, (E) CH3COOC2H5.
Let’s start by drawing the
structures of methanoic acid and methanol. The suffix -oic acid indicates that
methanoic acid is a carboxylic acid. Carboxylic acids are composed of a
carbonyl group, a carbon atom double bonded to an oxygen atom, and a hydroxy
group. The meth- term of the name
indicates that this carboxylic acid only contains one carbon atom. As the carboxyl functional group
already contains one carbon atom, this means that the R group must be a hydrogen
atom. The name methanol also contains the
meth- term, indicating that the molecule only contains one carbon atom. The suffix -ol indicates that
methanol is an alcohol and contains a hydroxy group.
As carbon atoms tend to form four
bonds, we complete the structure of methanol by adding three hydrogen atoms. The question tells us that these
two molecules react to produce an ester. This type of reaction is called
esterification. More specifically, the
esterification of a carboxylic acid with an alcohol is called Fischer
esterification. This reaction is typically carried
out in the presence of an acid catalyst such as sulfuric acid. Over the course of this reaction,
the hydroxy group of the carboxylic acid is replaced by the alkoxide group of the
alcohol. This produces an ester and
water. This ester only contains two carbon
atoms.
Looking at the answer choices, we
can eliminate answer choice (A), (C), (D), and (E), as each of these formulas
contains more than two carbon atoms. To verify that answer choice (B) is
the correct answer, let’s write the condensed formula of the ester we produced. The condensed formula is
HCOOCH3. This formula matches answer choice
(B). Thus, the ester obtained when
methanoic acid reacts with methanol is answer choice (B), HCOOCH3.
