Chapter 14, Problem 6MCP

(a)

Interpretation Introduction

Interpretation:

The statement “benzoic acid is an aliphatic carboxylic acid” has to be indicated as true or false.  The reason for the false statement has to be described.

Answer to Problem 6MCP

The given statement is false because benzoic acid is an aromatic carboxylic acid.

Explanation of Solution

Benzoic acid is the simplest aromatic carboxylic acid.  It is aromatic due to the presence of a benzene ring in its chemical structure.

The structure of benzoic acid is,

The statement “benzoic acid is an aliphatic carboxylic acid” is false because it is an aromatic carboxylic acid due to the presence of benzene ring.

(b)

Interpretation Introduction

Interpretation:

The statement “benzoic acid has a lower boiling point than benzaldehyde” has to be indicated as true or false.  The reason for the false statement has to be described.

Answer to Problem 6MCP

The given statement is false because benzoic acid has higher boiling point than benzaldehyde due to strong intermolecular hydrogen bonding and strong dipole-dipole interactions.

Explanation of Solution

Benzoic acid is a carboxylic acid and benzaldehyde is an aldehyde.

Carboxylic acids have strong intermolecular hydrogen bonding with each other and strong dipole-dipole attractions.

The presence of polar carboxyl group and intermolecular hydrogen bonding makes these acids have higher boiling points.  The presence of dimers increases the strength of the van der Waals dispersion forces, which makes them have high boiling points.

Aldehydes have higher boiling points when compared to ether or alkane, representing the presence of weak intermolecular dipole-dipole forces.  The carbonyl group is polar due to the presence of oxygen, which is more electronegative than carbon and forms a partially charge dipole.

Therefore, benzoic acid has higher boiling point than benzaldehyde due to strong intermolecular hydrogen bonding and strong dipole-dipole interactions.

Hence, the statement “benzoic acid has a lower boiling point than benzaldehyde” is false.

(c)

Interpretation Introduction

Interpretation:

The statement “benzoic acid reacts with ethanol to form ethyl benzoate” has to be indicated as true or false.  The reason for the false statement has to be described.

Answer to Problem 6MCP

The given statement is true.

Explanation of Solution

Benzoic acid on reaction with ethyl alcohol produces ethyl benzoate and water. 

The chemical reaction is,

The statement “benzoic acid reacts with ethanol to form ethyl benzoate” is true.

(d)

Interpretation Introduction

Interpretation:

The statement “benzoic acid has molecular formula of ${\text{C}}_{\text{7}}{\text{H}}_{\text{6}}\text{O}$” has to be indicated as true or false.  The reason for the false statement has to be described.

Answer to Problem 6MCP

The given statement is false because the molecular formula of ${\text{C}}_{\text{7}}{\text{H}}_{\text{6}}{\text{O}}_{\text{2}}\text{.}$

Explanation of Solution

Benzoic acid is an organic compound with molecular formula of ${\text{C}}_{\text{7}}{\text{H}}_{\text{6}}{\text{O}}_{\text{2}}\text{.}$

Hence, the statement “benzoic acid has molecular formula of ${\text{C}}_{\text{7}}{\text{H}}_{\text{6}}\text{O}$” is false.

(e)

Interpretation Introduction

Interpretation:

The statement “benzoic acid is structural isomer of xylene” has to be indicated as true or false.  The reason for the false statement has to be described.

Answer to Problem 6MCP

The given statement is false because the structural isomers of benzoic acids are tropolone, salicyladehyde, $\text{3-hydroxybenzaldehyde}$ and $\text{4-hydroxybenzaldehyde}\text{.}$

Explanation of Solution

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

The molecular formula of benzoic acid ${\text{C}}_{\text{7}}{\text{H}}_{\text{6}}{\text{O}}_{\text{2}}\text{.}$ is 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 “benzoic acid is structural isomer of xylene” is false because the structural isomers of benzoic acids are tropolone, salicyladehyde, $\text{3-hydroxybenzaldehyde}$ and $\text{4-hydroxybenzaldehyde}\text{.}$

(f)

Interpretation Introduction

Interpretation:

The statement “benzoic acid is more water soluble in phenol” has to be indicated as true or false.  The reason for the false statement has to be described.

Answer to Problem 6MCP

The given statement is false because phenol is more water soluble than benzoic acid due to its ability to form hydrogen bond with water molecules.

Explanation of Solution

Phenols are water soluble to some extent.  This is due to its ability to form hydrogen bonding with water molecules.  However, the large part of phenol molecule is the phenyl group that is non-polar and hence its solubility is limited in water.

Whereas, benzoic acid is insoluble in water because of the presence larger nonpolar benzene ring in the structure that cannot be water-soluble.

The statement “benzoic acid is more water soluble in phenol” is false because phenol is more water soluble than benzoic acid due the ability of phenols to form hydrogen bond with water molecules.

(g)

Interpretation Introduction

Interpretation:

The statement “sodium benzoate is food preservative and is produced by neutralization of benzoic acid with sodium hydroxide” has to be described as true or false. If the statement is false, the reason that it is false has to be described.

Answer to Problem 6MCP

The given statement is true.

Explanation of Solution

The reaction of benzoic acid with sodium hydroxide yields sodium salt of benzoic acid and water.  The protons of the acid are removed by the ${\text{OH}}^{\text{-}}$ of the base to form water and the cation of the base forms the salt of the benzoic acid.

The reaction is,

The statement “sodium benzoate is food preservative and is produced by neutralization of benzoic acid with sodium hydroxide” is true.