OCR GCSE Chemistry B C4 Material Choices Exam Questions

About OCR GCSE Chemistry B C4 Material Choices

Chapter C4 asks how chemists choose the right material for a job and what happens to it afterwards. On OCR Chemistry B you use data to compare metals, ceramics, polymers, glass and composites, then explain their properties using bonding and structure, from giant covalent diamond and graphite to polymer chains. You study nanoparticles, including fullerenes and graphene, and their surface area to volume ratio, and finish with recycling, corrosion and life cycle assessment. Separate chemistry adds addition and condensation polymers. It links back to bonding in C2 and C3. Expect data interpretation, structure and property explanations and surface area calculations.

What you need to know

• C4.1 Choosing materials Compare materials using data on strength, stiffness, hardness, density and melting point to match a product's specification. Alloys are harder than pure metals because different sized atoms disrupt the layers so they cannot slide easily.
• C4.2 Polymers Separate chemistry only: addition polymers form when the C=C double bonds in alkene monomers open. Condensation polymers such as polyesters and polyamides form from monomers with two functional groups, releasing a small molecule such as water. DNA, proteins and starch are natural polymers.
• C4.3 Bonding and structure Polymers have strong covalent bonds within chains and weaker forces between chains. Diamond and graphite are giant covalent allotropes of carbon: diamond is very hard with each carbon bonded to four others, while graphite has layers that slide and delocalised electrons that conduct.
• C4.4 Nanoparticles Nanoparticles are 1 to 100 nm across and have a very large surface area to volume ratio, so they can be very effective catalysts. Fullerenes, nanotubes and graphene have useful properties, but possible health and environmental risks are not fully understood.
• C4.5 End of life A life cycle assessment considers raw materials, manufacture, use and disposal. Reuse usually needs less energy than recycling. Separate chemistry adds rusting of iron in water and oxygen, prevented by barriers or sacrificial protection with zinc.

Common mistakes in C4 Material Choices

• Saying graphite conducts because of free ions. It conducts because each carbon has one delocalised electron that can move between the layers.
• Explaining a polymer's low melting point by breaking covalent bonds. Melting overcomes the intermolecular forces between chains.
• Writing that nanoparticles have a large surface area. The key idea is a large surface area to volume ratio, which increases as particle size decreases.
• Thinking recycling always beats everything. Reuse often uses less energy, and recycling depends on collection, sorting and transport costs.
• Saying iron rusts in air alone. Rusting needs both oxygen and water.

Try three C4 Material Choices exam-style questions