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

Short answer

The correct answer is (c): 2, 3, and 4.

Step-by-step solution

Understand the Properties of Polymers

Polymers are large molecules formed by repeating structural units. Due to their size, they tend to have high molecular weight, so option (1) is incorrect. Polymers also often have high viscosity because they form long chains that create resistance to flow, meaning option (2) is correct.

Evaluate Light Scattering by Polymers

Light scattering occurs due to the non-uniform structure of polymers, which interferes with the passage of light. This implies option (3) is true.

Assess Charge on Polymers

Most polymers in their native state do not carry a charge, but certain synthetic polymers can carry charges depending on their functional groups. However, generally speaking, unmodified polymers are neutral, so option (4) is also generally true.

Match Correct Options to Given Answers

From the assessment, the true statements about polymers are options 2, 3, and 4. Therefore, the correct choice is (c).

Key concepts

High Viscosity in Polymers

Polymers are fascinating materials primarily because of their unique structural characteristics. These large molecules are made up of repeating units called monomers. When these monomers join in long chains, they create a significant resistance to flow, which results in high viscosity. Viscosity is the measure of a fluid's resistance to deformation or flow. In the case of polymers, think of these long chains as entangled spaghetti. The more entangled the chains, the tougher it is for them to slide past each other, leading to high viscosity. - **Chain Length and Entanglement:** Longer chains lead to more entanglement and higher viscosity. - **Cross-Linking:** Increased cross-links between chains can also enhance viscosity. The high viscosity in polymers is a core reason they are used in making adhesives, coatings, and plastics. This property allows them to be shaped into a wide variety of forms and retain their structure.

Light Scattering by Polymers

Light scattering in polymers generally arises due to the irregular arrangement of their molecular chains. This irregularity causes variations in the refractive index, which affects how light is transmitted or scattered. When light travels through a polymer, it encounters different refractive indices due to chain orientations, side groups, or inclusions like air bubbles or additives. These differences cause the light to bend or scatter in multiple directions. - **Factors Affecting Light Scattering:** - **Molecular Structure:** Variations in molecular structure create non-uniformity. - **Additives and Inclusions:** Presence of other materials within the polymer can scatter light. Light scattering is why many polymers appear opaque or translucent, rather than completely transparent. This property can be particularly useful in applications like optical devices and packaging materials.

Neutral Charge in Polymers

Polymers in their natural or unmodified state typically possess no overall electric charge. This behavior is attributed to the balance between the positive and negative charges in the molecules that make up polymers, leading to a neutral charge overall. However, it is also possible for certain synthetic polymers to be designed with charged groups. These groups turn the polymer into an ionomer. The functional groups used, like carboxylate or ammonium, contribute to the overall charge. - **Neutral vs. Charged Polymers:** - **Neutral Polymers:** Majority of natural polymers and many synthetic polymers are neutral. - **Charged Polymers:** Specific functional groups can introduce charges. The neutral charge state of most polymers is advantageous, as it makes them less likely to react with other substances, which is why they are popular in many chemical-resistant and stable applications.