Question

Explain why nylon reacts with acid, whereas polyethylene is inert toward acid.

Short answer

Answer: Nylon reacts with acids due to the presence of amide functional groups that can act as a base and accept protons, whereas polyethylene does not contain any functional groups capable of participating in an acid-base reaction, and thus remains inert toward acids.

Step-by-step solution

Compare the chemical structures of nylon and polyethylene

To begin, let's examine the chemical structures of both polymers. Nylon belongs to a family of polymers called polyamides, which are characterized by the presence of amide functional groups (–CONH–) within their repeating units. In the case of nylon-6,6 (a common type of nylon), the repeating unit is as follows: \[ \underset{\text{nylon-6,6}}{-[NH-(CH_2)_6-NHCO(CH_2)_4CO]-} \] On the other hand, polyethylene is a simple polymer consisting of carbon and hydrogen atoms joined by single bonds. The repeating unit in polyethylene is: \[ \underset{\text{polyethylene}}{-[CH_2CH_2]-} \]

Discuss acid-base reactions

An acid-base reaction occurs when an acid (a species that can donate a proton) reacts with a base (a species that can accept a proton). A typical example of an acid-base reaction is the reaction between hydrogen chloride (HCl) and ammonia (NH\(_3\)): \[ NH_3 + HCl \rightarrow NH_4^+ + Cl^- \]

Analyze the reactivity of nylon with acids

Now let's focus on the amide functional group (–CONH–) present in nylon. The nitrogen atom in the amide group has a lone pair of electrons, which can act as a base and accept a proton from an acid. Therefore, the amide group is reactive towards acids. For example, if nylon reacts with a strong acid, like hydrochloric acid (HCl), it will produce a protonated amide group (–CONH\(_{2}^+\)) and a chloride ion (Cl\(^-\)): \[ -CONH- + HCl -\rightarrow -CONH_2^+ + Cl^- \]

Analyze the inertness of polyethylene with acids

In contrast, polyethylene lacks any functional group capable of donating or accepting protons. As a result, polyethylene will not react with acids, and thus is considered to be inert towards them. In conclusion, nylon reacts with acids due to the presence of amide functional groups that can act as a base and accept protons, whereas polyethylene does not contain any functional groups capable of participating in an acid-base reaction and, therefore, is inert toward acids.

Key concepts

Chemical Structures

Understanding the chemical structures of nylon and polyethylene is key to grasping their reactivity. Nylon is a polyamide, meaning it is made up of repeating units connected by amide groups \((-CONH-)\). These units in nylon-6,6 consist of long carbon chains interrupted by the amide linkage, which provides sites for chemical interaction.

On the other hand, polyethylene is much simpler. It is formed by repeating units of ethylene \((-CH_2CH_2-)\), creating a chain of carbon atoms connected by single bonds. This simple structure provides stability but lacks functional groups that can easily react with other substances.

• **Nylon's amide linkage**: Provides reactive sites.
• **Polyethylene's simplicity**: Lacks reactive groups.

Acid-Base Reactions

Acid-base reactions are fundamental chemical processes where an acid donates a proton \((H^+)\) and a base accepts it. These interactions are crucial in determining how substances like nylon and polyethylene react with acids.

While simple, polyethylene doesn't engage in acid-base reactions due to the absence of reactive sides that can donate or accept protons.

Nylon, with its amide group, behaves differently. Here, the nitrogen atom in the amide group has a lone pair of electrons, enabling it to act as a base. When it encounters an acid, it can accept a proton, making nylon more chemically reactive in the presence of acids.

• **Nylon's nitrogen**: Can accept protons due to lone pairs.
• **Polyethylene's structure**: Inert, no reactivity with acids.

Amide Functional Group

The amide functional group found in nylon is a game-changer when it comes to reactivity with acids. The structure \((-CONH-)\) is crucial due to the nitrogen atom, which carries a lone pair of electrons.

This pair makes the amide group capable of accepting protons from acids. When nylon reacts with a strong acid like hydrochloric acid, the nitrogen will take on a proton, forming a protonated amide. This process can drastically alter the polymer's properties.

Polyethylene, in contrast, lacks such functional groups. Thus, it remains unaffected by acids, preserving its properties.

• **Amide's lone pair**: Key to interaction with acids.
• **Polyethylene**: No amide group, no reaction with acids.