Video Transcript
Which of the following statements
about alcohols is incorrect? (A) They react with sodium to form
the corresponding alkoxide. (B) They have higher boiling points
in comparison to other hydrocarbons having equal molecular masses. (C) They could be prepared from the
reaction of alkyl halides with strong alkalis. (D) They are soluble in water due
to the formation of intermolecular hydrogen bonds with water molecules. Or (E) they have an acidic effect
on litmus paper.
Alcohols are organic compounds that
contain at least one hydroxy functional group. Alcohols have some fascinating
chemical and physical properties. The question presents some
statements that might describe the properties of an alcohol. We need to identify which of the
statements is incorrect.
Answer choice (A) describes a
reaction between an alcohol and sodium metal. When an alcohol reacts with sodium
metal, an oxidation–reduction reaction occurs. Hydrogen gas is liberated, and a
new ionic species is produced. The species is a sodium
alkoxide. So the reaction of an alcohol with
sodium does produce alkoxide anions. As answer choice (A) is a true
statement and we need to identify the statement that is incorrect, answer choice (A)
cannot be the answer to this question.
Hydrocarbons are organic molecules
that only consist of carbon and hydrogen atoms. Hydrocarbon molecules are held
together by weak dispersion forces. Alcohols contain a hydrogen atom
bonded to an oxygen atom. There’s a large electronegativity
difference between these two atoms, which makes alcohols polar molecules.
Alcohol molecules are held together
by a combination of dispersion forces and strong intermolecular forces called
hydrogen bonds that occur due to the large electronegativity difference in the
molecules. As stronger forces exist between
alcohol molecules than hydrocarbon molecules, more energy will be required to
separate the alcohol molecules during boiling. Thus, alcohols will have higher
boiling points in comparison to other hydrocarbons that have equal molecular
masses. So answer choice (B) is true and
cannot be the answer to this question.
Just as alcohol molecules can form
strong hydrogen bonds with one another, they can also form strong hydrogen bonds
with water molecules. Because of these attractive
electrostatic interactions between alcohol and water molecules, alcohol molecules
tend to be more soluble in water than other nonalcohol organic molecules like
alkanes and alkenes. So answer choice (D) is also a true
statement and cannot be the answer to this question.
Answer choice (C) states that
alcohols can be prepared by reacting alkyl halides with strong alkalis, such as
sodium hydroxide. When these substances react, the
halogen of the alkyl halide is substituted with the hydroxy group of the alkali. This produces an alcohol and a
salt. As alcohols can be prepared by
reacting alkyl halides with strong alkalis, answer choice (C) cannot be the answer
to the question.
We are left with answer choice
(E). Blue litmus paper will turn red in
the presence of a strong enough acid. Alcohols do have the ability to
donate hydrogen ions in solution, so they can be considered acids. However, alcohols are only weakly
acidic and are not strong enough to have an effect on blue litmus paper. Therefore, answer choice (E) is an
incorrect statement.
In conclusion, the statement about
alcohols that is incorrect is answer choice (E). They have an acidic effect on
litmus paper.
