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OCR 21st Century Science C2

Paper bags are often replaced with plastic ones, which are []er and also w[] lighter--waterproof--.
The soles of shoes have to be f[], hard w[]ring, and st[]; also, they must not cr[] when they bend - they have to be tough. flexible--hard wearing--strong--crack--. A good choice is s[]tic []
Silk and wool are p[] f[]es, while paper cosists of c[]se f[]es protein fibres--cellulose fibres--. Give an example of a cellulose then one of a protein fibre:
In clothing natural f[]s are replaced with s[] ones fibres--synthetic--, which may be easier to w[], hold their s[] better, or be available in a wider range of c[]s wash--shape--colours--.
The properties of a product (including effectiveness and durability) can be related to its composite materials.
Materials can be obtained or made from []ing things living things; examples include s[], w[], p[] and c[]
There are s[]c materials that are alternatives to materials from living things synthetic--.
R[] materials from the Earth's [] can be used to make synthetic materials raw--crust--.
In a chemical reaction, the number of atoms of each [] must be the same in the products as in the reactants element.
Crude oil consists mainly of []s hydrocarbons.
Hydrocarbons are c[] molecules of varying [] chain--lengths--; they are made only from [] and [] atoms carbon--hydrogen--.
A small percentage of crude oil is used for c[] s[] chemical synthesis, but most of it is used as fuels.
[#c3#]Fractional distiallation seperates a [] into a number of different p[]ts, called [] mixture--parts--fractions--.
Fractional distillaition works because the different substances in the mixture have different [] []s boiling points. Substances with high boiling points condense at the [], while substances with low boiling points condense at the [] bottom--top--.
The petrochemical industry refines crude oil by [] [] fractional distillation; []ns are separated into fractions of different [] [] hydrocarbons--boiling points-- in order to produce f[]s, l[]s and the raw materials for c[] s[] fuels--lubricants-- chemical synthesis--.
The forces between hydrocarbon molecules [] as the size of the molecules increases increases--.
As the strength between hydrocarbon molecules in crude oil increases, the amount of [] needed for them to break out of a liquid and form a gas []ses energy--increases: hence as the strength of the forces between hydrocarbon molecules in crude oil increases, the temperature at which the liquid []s increases boils--.
A monomer is a single c[]nd m[] compound molecule whose molecules can be b[] to other identical molecules to form a [] bonded--polymer--; these polymers are very [] and the process described is called [] long--polymerisation--.
Wood is often replaced with p[]s plastics, which are l[]er and do nor ro[] or require pa[] lighter--rot--painting--.
By knowing about the molecular structure of materials, it's possible to produce a wide range of different polymers with p[]es that make them each suited to a particular use properties--.
The properties of polymers depend on how their [] are arranged and held together molecules--.
A polymer will melt when the inter[] forces are overcome intermolecular--. The stronger the forces, the more energy needed to s[] them separate--, thus the higher the material's m[]ing p[], st[], st[]ness and h[]ness melting point--strength--stiffness--hardness--.
A polymer molecule is a long [] of atoms chain--.
The effect on the properties of increasing the length of a polymer chain is similar to the effect of increasing c[]: the material become s[] and s[] and the melting point gets [] crystallinity--stronger--stiffer--higher--; increasing the chain length of a polymer also makes it less flexible; by increasing chain length, the material also becomes more likely to get tangled, which can make the modified material []er than the original stronger--.
When modifying with cross-links: a chemical, often sulfur, is added to the material, making []-[] between the [] cross-links--molecules--.
As a result of the creation of cross-links, the molecules of the polymer are locked into a regular [] arrangement. This stops them slipping [...] over each other and makes the material less [], but []er and []er flexible--stronger--harder--; harder and stronger as it's thus more difficult to [] the []-[] []es break the inter-molecular forces.
The creation of cross-links gives the material a [] melting point higher--, because more [] is needed for the molecules to separate and break out of the solid energy--.
Plasticization involves adding a [] (usually an [] liquid with small []) to the material plasticizer--oily--molecules--. The small moleculess then sit [] the polymer chains between--, hence the polymer chains would then be ... further apart.
As a result of the presence of platicizers, polymer chains become further apart. This [] the forces between them weakens--, so less energy is needed to [] them and they [] over each other more [] separate--slide--easily--. This means the polymer is []er and more [], and has a [] melting point. softer--flexible--lower--.
The amount of a polymer that forms crystals is called its crystallinity. The higher the crystallinity of a polymer, the s[] and s[] and d[] the material becomes stronger--stiffer--denser; also, the melting point gets higher.
In crystalline polymers, the molecules are arranged in [] [] neat lines.
Nanotechnology involves structures that are about the size of some molecules.
Nanotechnology is the u[] and c[] of structures that are very [] use--control--small-- (with sizes from [] to [] []metres] 1--100--nanometres--.
Nanoparticles can occur naturally (for example in s[]) seaspray, by a[] (for example as the smallest p[] from c[] of f[]), and by d[] accident--particulates--combustion--fuels--design.
The nanoparticles of a material show different [] compared to larger particles of the same material properties--; one of the reasons for that is the nanoparticles' larger ratio for s[] a[] to [] surface area to volume. One reason that the ratio could be useful is that the atoms on a material's surface are more [] than those in the centre reactive--.
Nanoparticles can be used to modify materials' properties. For example: silver nananoparticles are used to give fibres [] properties antibacterial; also, nanoparticles are added to p[]s for sports equipment to make them [] plastics--stronger--.
Nanoparticles may have harmful effects on h[] health, and there is concern that products with nanoparticles are being introduced before these effects have been fully investigated.
Data is more reliable if it can be r[] repeated.
For a set of data has values a, b, c, d, e (from lowest to highest): the range is a-e.
The accuracy of a measurement is affected by the []y of the used equipment and the s[] of the coordinator(s) quality--skill--.
For data to be reliable, the difference between values from different sets of measurements must be very small.
A factor that's kept the same throughout an experiment is called a control variable.
In an experiment, the independedent variable is the variable that's []ed variated.
When the independent variable changes, it causes the [] variable to change dependent--.
A result from an experiment can also be called an o[] outcome--.
An outcome that's far from other outcomes or doesn't fit the general pattern is called an outlier. If you want to do calculations with your outcomes, [] the outlier exclude.
If the ranges of two sets of data do not overlap and the mean of either isn't in the range of the other: then there's a real difference.
All the materials we use are []s or m[]es of [] chemicals--mixtures of chemicals--, and include m[]s, c[]ics and p[] metals--ceramics--polymers.
In fractional distillation, a tall column is fitted above a m[] mixture, with several [] coming off at different [] condensers--heights--. The column is [] at the bottom and [] at the top hot--cool--.
Created by: Toluo
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