C2 - Material Choices

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Flashcards by franimal, updated more than 1 year ago
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Cambridge IGCSE Chemistry Flashcards on C2 - Material Choices, created by franimal on 10/20/2013.

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Question Answer
Why do materials need the right properties? Otherwise they will be unsuited to the task, such as metal being a bad material for a feather duster.
What's the definition of a polymer? A material made of very long molecules, formed by joining lots of small molecules (monomers) together.
There are both synthetic and natural polymers. Why are we using more synthetic polymers than 20 years ago. There's now a lot more variety, so new materials are made more suited to our needs than natural alternatives.
A material can be strong in tension and/or strong in compression. What does this mean? Tension: hard to pull apart. Compression: hard to buckle.
What is a stiff material? The opposite of flexible, difficult to bend or stretch.
How can you tell if one material is harder than another? The harder material will always scratch the softer one.
If a material is heavy for its volume, what is it? Dense, as in a high density.
What is accuracy? How close a measurement is to its true value.
What is repeatable and reproducible? Repeatable: under the exact same conditions, the result wouldn't change. Reproducible: under different conditions the result wouldn't change.
Why do the factors not being tested have to be controlled, eg temperature? To make it a fair test, so that the result is more accurate and not interfered with.
What are the properties of a material based upon? Their atomic structure and the way the molecules line up.
How many nanometres in a metre? 1,000,000,000,000 or 1 trillion
If a molecule such as wax has few atoms in each molecule, what's the effect? The wax is brittle and easy to melt because the molecules are too small to tangle and can separate with ease.
On a molecular level what does vulcanisation cause? Cross-links form between polymer chains, locking them in place.
What is plasticiser and what does it do? An oily liquid with small molecules that sits between polymer chains, keeping them apart. This makes the polymer soft and flexible.
What is LDPE or a non-crystalline polymer? Low Density Polythene, a form of polythene where there are branches on the polymer chains, making it irregular.
What is HDPE or a crystalline polymer? High Density Polythene is made by forming polythene on a catalyst, so it forms packed and dense, without branches.
What is crude oil? The unrefined oil recovered from the Earth's crust. Not very useful.
What can crude oil be used for? Name three. Bottled gas, petrol for vehicles, chemicals, jet fuel, paraffin for heating, diesel fuels, fuel for central heating, lubricants, waxes, polishes, roads or roofing.
How is crude oil separated into groups of same-sized molecules? By fractional distillation - the oil is heated, and then goes into a tower. The smaller molecules rise to the top because they take the least energy to become a gas.
What is nanotechnology? The use and control of structures called nanoparticles, which are tiny, tiny particles.
Why do nanoparticles often have unusual or reactive properties? The atoms on the surface are more reactive, and because nanoparticles are smaller they have more outer atoms.
Name three uses for nanoparticles. Bus fuel, geckos' feet, bandages, proteins that control biological processes, sunscreen, tennis balls, electronic paper, clothing, self-cleaning windows.
Why are some doctors worried about nanoparticles? They theorise that nanoparticles could be small enough to enter the brain through the blood, making normal chemicals toxic.
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