Problem 86 - A Complete Resource Book in Chemistry for JEE Main

Question

Which is true about polymers? (1) polymers have low molecular weight (2) polymers have high viscosity (3) polymers scatter light (4) polymers do not carry any charge (a) 1,2 and 3 (b) 1,2 and 4 (c) 2,3 and 4 (d) 1,3 and 4

Step-by-Step Solution

Answer

Correct option: (c) 2, 3, and 4.

Step 1: Understanding Polymers

Polymers are large molecules that are composed of repeating structural units, typically connected by covalent chemical bonds. They are known for having high molecular weights, not low molecular weight.

Step 2: Analyzing Viscosity

Polymers frequently have high viscosity. This property is due to the long chains of molecules that can become tangled with one another, thus increasing the thickness and resistance to flow.

Step 3: Light Scattering Property

Polymers can scatter light because they often have irregular or amorphous structures that can disrupt light passage and cause scattering.

Step 4: Charge Nature of Polymers

While many polymers are neutral and do not carry any charge, some can be charged, depending on their chemical structure and environment.

Step 5: Evaluating Options

(1) is incorrect because polymers typically have high molecular weight. (2) is true since polymers have high viscosity. (3) is true because polymers scatter light. (4) is generally true, though some exceptions exist. Evaluating the options, (c) 2, 3, and 4 matches this observation.

Key Concepts

Molecular Weight of Polymers

When we talk about the molecular weight of polymers, we're discussing the size of these large molecules. Polymers are made up of long chains of repeating units known as monomers, which are linked together. This chain formation gives polymers a high molecular weight, contrasting with smaller molecules that have low molecular weights.

The molecular weight is significant because it affects the physical properties of the polymer, such as strength, toughness, and durability.

• Number-average molecular weight (M_n): This is the total weight of all polymer molecules in a sample divided by the total number of polymer molecules.
• Weight-average molecular weight (M_w): This considers the size of individual molecules, with more massive molecules making more contributions to the weight average.

Understanding these concepts helps in determining a polymer's applications and processing conditions.

Viscosity of Polymers

The viscosity or thickness of a polymer is an essential property that describes how it flows. Polymers, due to their long-chain molecular structure, typically have high viscosity compared to simpler liquids like water. This elevated viscosity arises from the intertwining and entanglement of these long molecular chains.

Higher viscosity means more resistance to flow. It can be affected by:

• Temperature: As temperature increases, viscosity usually decreases, making the polymer flow more easily.
• Molecular weight: Generally, polymers with higher molecular weights exhibit higher viscosity.
• Concentration: Increasing polymer concentration in a solution raises its viscosity.

Understanding viscosity helps in processing polymers, such as during injection molding or extrusion.

Light Scattering in Polymers

Light scattering is a phenomenon that occurs when light travels through a medium and is systematically deviated in various directions. In polymers, scattering happens because of their complex structures. Many polymers have amorphous regions where the arrangement of the molecules is irregular, and it's in these areas that light scattering mostly occurs.

Scattering of light in polymers has several practical implications, including:

• Determining molecular size: Scientists use light scattering techniques to measure the size and shape of polymer chains.
• Opacity and Transparency: Scattered light affects how clear or opaque the polymer appears. High scattering can lead to a translucent or opaque appearance.

Understanding light scattering helps in designing materials with specific optical properties for use in lenses, films, and packaging.

Charge Properties of Polymers

Polymers are typically neutral, meaning they do not carry a charge. However, their charge properties can vary based on their chemical structure and the environment in which they're used. Some polymers can become charged, either negatively or positively, through processes like addition of specific functional groups or conducting synthesis under specific conditions.

This charge behavior can affect:

• Solubility: Charged polymers may exhibit different solubility compared to their neutral counterparts.
• Interactions: Charged polymers can interact with other charged species, making them useful for applications such as ion-exchange resins or drug delivery systems.
• Conductivity: Conducting polymers, which carry charge, are essential in electronics and smart materials.

Understanding these charge properties allows for the development of specialized polymers for specific applications, enhancing their functionality and versatility.