Chapter 14, Problem 2MCP

(a)

Interpretation Introduction

Interpretation:

The statement “Hexanoic acid has a lower melting point than hexanal” 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 2MCP

The given statement is false because hexanoic acid has a higher melting point than hexanal due to exclusive intermolecular hydrogen bonding and strong dipole-dipole attractions.

Explanation of Solution

Hexanoic acid is a carboxylic acid and hexanal is an aldehyde.

Carboxylic acids have high melting point when compared to alcohols, aldehydes and alkanes.  This is because carboxylic acids could form intermolecular hydrogen bonds with one other, they also have strong dipole-dipole attractions and also due to the presence of polar carboxyl group, which gives them higher melting points than alcohols, aldehydes and ketones.

Therefore, hexanoic acid has a higher melting point than hexanal.  This higher melting point of hexanoic acid is due to intermolecular hydrogen bonding and strong dipole-dipole attractions.

Hence, the statement “Hexanoic acid has a lower melting point than hexanal” is false.

(b)

Interpretation Introduction

Interpretation:

The statement “Hexanoic acid has a higher boiling point than hexanol” 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 2MCP

The given statement is true.

Explanation of Solution

Hexanoic acid is a carboxylic acid and hexanol is an alcohol.

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.

Therefore, hexanoic acid has a boiling point than hexanol.  This higher boiling point of hexanoic acid is due to intermolecular hydrogen bonding and strong dipole-dipole attractions.

Hence, the statement “Hexanoic acid has a higher boiling point than hexanol” is true.

(c)

Interpretation Introduction

Interpretation:

The statement “Hexanoic acid is not soluble 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 2MCP

The given statement is true.

Explanation of Solution

Hexanoic acid is a saturated fatty acid with a medium chain length of six carbons.  The carboxylate group $\text{-}\left(\text{COOH}\right)$ is highly soluble in water, whereas the oily hydrocarbon tail is nearly soluble.  The overall solubility of the fatty acid is determined by these factors.  If the oily tail is short, the carboxylate group dominates and the water solubility is high.  For long and medium chain fatty acids, the tail dominates and the water solubility is extremely low or insoluble.

Therefore, hexanoic acid is barely soluble in water or insoluble in water.  Hence, the statement “hexanoic acid is not soluble in water” is true.

(d)

Interpretation Introduction

Interpretation:

The statement “Hexanoic acid is polar” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Concept Introduction:

Carboxylic acid consists of carboxyl group.  A carboxyl group is a functional group consisting of carbonyl group $\text{(C=O)}$ with hydroxyl group $\text{(O-H)}$ attached to the same carbon atom.  Carboxylic acids are used as precursors to form other compounds such as esters, aldehydes and ketones.

Answer to Problem 2MCP

The given statement is true.

Explanation of Solution

The functional group present in carboxylic acids is carboxyl group $\text{(-COOH)}$.

Carboxylic acids are polar in nature.  This is due to the presence of the carboxyl group that comprises of two polar functional groups namely, carbonyl group and hydroxyl group.  The carbonyl group is polar due to the presence of oxygen, which is more electronegative than carbon.  This produces a dipole in which oxygen carries a partial negative charge and carbon carries a partial positive charge.  This allows intermolecular dipole-dipole attractions.  The hydroxyl group is polar because oxygen is higher electronegativity than hydrogen and oxygen atom has two unpaired electrons.  This results in the formation of polar bond in which oxygen carries a partial negative charge and hydrogen carries a partial positive charge.  This results in the formation of hydrogen bonding.

Therefore, hexanoic acid is polar in nature due to presence of polar carbonyl and hydroxyl groups.  Hence, the statement “Hexanoic acid is polar” is true.

(e)

Interpretation Introduction

Interpretation:

The line formula of hexanoic 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 2MCP

The given line formula of hexanoic acid is false because it represents hexanal.

Explanation of Solution

The given line formula is,

The above line formula represents hexanal.

Hence, the given line formula is false because it represents hexanal.

The line formula of hexanoic acid is,

(f)

Interpretation Introduction

Interpretation:

The statement “Hexanoic acid is solid at room temperature” 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 2MCP

The given statement is false because it appears as an oily liquid at room temperature.

Explanation of Solution

Hexanoic acid appears as a colorless oily liquid with an odor that is fatty, cheesy and waxy.  It is found naturally in various animal fats and oils.

It has chemical formula ${\text{CH}}_{\text{3}}{\left({\text{CH}}_{\text{2}}\right)}_{\text{4}}\text{COOH}\text{.}$

The common name of hexanoic acid is caproic acid.  It is a saturated medium-chain fatty acid with six-carbon backbone.

Hence, the statement “Hexanoic acid is solid at room temperature” is false because it is an oily liquid in room temperature.

(g)

Interpretation Introduction

Interpretation:

The statement “Oxidation of hexanoic acid would produce a primary alcohol” 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 2MCP

The given statement is false because the oxidation of primary alcohol (hexanol) would produce hexanoic acid.

Explanation of Solution

Hexanoic acid can be produced by the oxidation of hexanol that is primary alcohol.  The equation is,

Therefore, the statement “Oxidation of hexanoic acid would produce a primary alcohol” is false because primary alcohols undergo oxidation to form hexanoic acid and not the vice-versa.

(h)

Interpretation Introduction

Interpretation:

The statement “Hexanoic acid is more oxidized than hexanal” 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 2MCP

The given statement is true.

Explanation of Solution

The presence of hydrogen bonding capabilities and the presence of two oxygen atoms makes them more oxidized than hexanal.

Hence, the statement “Hexanoic acid is more oxidized than hexanal” is true.

(i)

Interpretation Introduction

Interpretation:

The statement “The reaction of hexanoic acid with an ethanol molecule would produce an acetal” 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 2MCP

The given statement is false because an ester is produced when hexanoic acid is reacted with ethanol.

Explanation of Solution

The addition of an ethanol molecule to hexanoic acid results in the formation of ethyl hexanoate, an ester.  The reaction is,

The statement “Hexanoic acid reaction with an ethanol would produce an acetal” is false because an ester called ethyl hexanoate is produced when an ethanol molecule is added to hexanoic acid.

(j)

Interpretation Introduction

Interpretation:

The statement “The reaction of hexanoic acid with sodium hydroxide would produce sodium hexanoate” 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 2MCP

The given statement is true.

Explanation of Solution

The reaction of hexanoic acid with sodium hydroxide would produce sodium hexanoate and water.

The chemical reaction is,

Hence, the statement “The reaction of hexanoic acid with sodium hydroxide would produce sodium hexanoate” is true.

(k)

Interpretation Introduction

Interpretation:

The statement “The reaction of hexanoic acid with methanol would produce hexyl methanoate” 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 2MCP

The given statement is false because an ester named methyl hexanoate is produced when hexanoic acid is reacted with methanol.

Explanation of Solution

The addition of methanol to hexanoic acid results in the formation of methyl hexanoate, an ester.  The reaction is,

The statement “The reaction of hexanoic acid with methanol would produce hexyl methanoate” is false because an ester named methyl hexanoate is produced when hexanoic acid is reacted with methanol.

(l)

Interpretation Introduction

Interpretation:

The statement “Hexanoic acid could be produced by the oxidation of $\text{3-hexanone}$” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Explanation of Solution

The oxidation of $\text{3-hexanone}$ does not result in the formation of hexanoic acid because ketones are resistant to oxidation.  Hence, the statement “Hexanoic acid could be produced by the oxidation of $\text{3-hexanone}$” is false.