iGCSE Chemistry (0620) Core:11.8 Polymers: Exam Style Questions Paper 1- New Syllabus
▶️ Answer/Explanation
Detailed solution:
The repeat unit shown in the diagram is $-\text{CH}_2-\text{CH}_2-$, which is the repeat unit of poly(ethene), commonly known as polythene. The monomer used to make this polymer is ethene ($\text{CH}_2=\text{CH}_2$), which undergoes addition polymerisation where the carbon-carbon double bond breaks open and the molecules link together. Ethane ($\text{C}_2\text{H}_6$) is an alkane with only single bonds and cannot undergo addition polymerisation. Therefore, the polymer is poly(ethene) and the monomer is ethene, making option D the correct pairing.
▶️ Answer/Explanation
Detailed solution:
Plastics persist in the environment because they are not easily broken down. Property 2 (does not react with water) means that plastics won’t dissolve or be washed away by rain, rivers, or oceans—they simply persist. Property 3 (resistant to oxidation) means that plastics don’t degrade or break down when exposed to oxygen in the air, unlike many natural materials that rot or rust. These two properties directly explain why plastics accumulate and are difficult to remove from the environment. Being a poor conductor of electricity (1) and having low density (4) are properties of plastics but don’t directly explain why they are environmentally persistent. Therefore, properties 2 and 3 are the key reasons, making option C correct.
▶️ Answer/Explanation
Detailed solution:
Poly(ethene) is a very stable, unreactive addition polymer made up of long hydrocarbon chains. This stability means it is not biodegradable—microorganisms cannot break it down, and water does not decompose it. So when plastic bags end up in the ocean, they just sit there for potentially hundreds of years, accumulating over time because they do not decompose. Whether it is saturated or made from hydrocarbon monomers is not the direct reason for its persistence in the environment; it is the lack of decomposition that is the core problem.