Chapter 15, Problem 5MCP

(a)

Interpretation Introduction

Interpretation:

The statement “Aniline is an aromatic amine” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 5MCP

The given statement is true.

Explanation of Solution

Aniline is the simplest aromatic amine with the formula ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{NH}}_{\text{2}}\text{.}$  It consists of phenyl group attached to an amino group.  Hence, the statement “Aniline is an aromatic amine” is true.

(b)

Interpretation Introduction

Interpretation:

The statement “Aniline has a lower boiling point than benzoic acid” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 5MCP

The given statement is true.

Explanation of Solution

Aniline is an amine and benzoic acid is carboxylic acid.

The ability of primary and secondary amines to form $\text{N-H---N}$ hydrogen bond is reflected in their boiling points.  Because the nitrogen atom is less electronegative than the oxygen atom, the $\text{N-H}$ bond is less polar than the intermolecular hydrogen bonds formed in carboxylic acid.  Thus, amines have lower boiling points than carboxylic acid.  Therefore, the boiling point of aniline is lower than that of benzoic acid.  Hence, the given statement is true.

(c)

Interpretation Introduction

Interpretation:

The statement “Aniline is planar molecule” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 5MCP

The given statement is false because it is slightly pyramidalized molecule.

Explanation of Solution

Aniline is slightly pyramidalized molecule, with hybridization of the nitrogen between ${\text{sp}}^{\text{3}}\text{and}{\text{sp}}^{\text{2}}\text{.}$

Hence, the given statement is false.

(d)

Interpretation Introduction

Interpretation:

The statement “The molecular formula of aniline is ${\text{C}}_{\text{6}}{\text{H}}_{\text{6}}\text{N}$ has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 5MCP

The given statement is false because the molecular formula of aniline is ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{NH}}_{\text{2}}\text{.}$

Explanation of Solution

Aniline is the simplest aromatic amine with the formula ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{NH}}_{\text{2}}\text{.}$  It consists of phenyl group attached to an amino group.  The structure of aniline is,

Hence, the statement “Aniline has a molecular formula of ${\text{C}}_{\text{6}}{\text{H}}_{\text{6}}\text{N}$” is false because the molecular formula is ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{NH}}_{\text{2}}\text{.}$

(e)

Interpretation Introduction

Interpretation:

The statement “Aniline is a structural isomer of xylene” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 5MCP

The given statement is false because both aniline and xylene have different molecular formulas.

Explanation of Solution

Structural isomers are those with same molecular formula but differ in arrangement of atoms.

The molecular formula of aniline is ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{NH}}_{\text{2}}$ and its structure is,

The molecular formula of xylene is ${\text{C}}_{\text{8}}{\text{H}}_{\text{10}}$ and its structure is,

Both these are not structural isomers with each other.

Hence, the statement “aniline is structural isomer of xylene” is false because they have different molecular formulas.

(f)

Interpretation Introduction

Interpretation:

The statement “Aniline is more soluble than phenol” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 5MCP

The given statement is false because both aniline and phenol are sparingly soluble in water.

Explanation of Solution

Aniline does not form hydrogen bonds with water to a very large extent due to the presence of large hydrophobic ${\text{-C}}_{\text{6}}{\text{H}}_{\text{5}}$ group but it has the ability of form hydrogen bonds with water. 

The hydroxyl group of phenol is polar in nature, the oxygen is more electronegative than hydrogen, and hence it attracts shared electrons and acquires partial negative charge.  The hydrogen of hydroxyl group in phenol carries partial negative charge.  Phenol forms hydrogen bonding with water.  However, the large part of phenol molecule is phenyl group is non-polar, thus making it sparingly soluble in water.

Hence, the given statement is false because both aniline and phenol are sparingly soluble in water.

(g)

Interpretation Introduction

Interpretation:

The statement “Aniline produces phenylammonium ion in water” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 5MCP

The given statement is true.

Explanation of Solution

Aniline acts as bases, accepting ${\text{H}}^{\text{+}}$ when dissolved in water.  The nonbonding pair (lone pair) of electrons of the nitrogen atom could be shared with a proton ${\text{(H}}^{\text{+}}\text{)}$ from a water molecule, forming a phenylammonium ion.  Hydroxide ions are also formed, so the resulting solution is basic.  The reaction is,