Chemistry Reference
In-Depth Information
Figure 2.43
The combination of cellulose fi bres and lignin makes the
cell walls hard, thick and very strong. These properties reinforce the
cells against collapse.
Questions
1
Why are composite materials often used instead of
single materials?
2
Using the information in the text and any other
information available to you, give a use other than those
already mentioned for each of the following composite
materials:
a
reinforced concrete
b
glass-reinforced plastic
c
laminate
d
glass fi bre.
Figure 2.42
Bone is a composite material.
Checklist
After studying Chapter 2 you should know and understand the
following terms.
•
Accuracy in experimental work
The accuracy of each
measurement. It depends on the quality of the measuring
apparatus (e.g. the thermometer or electronic balance) and
on the skill of the scientists taking the measurement.
•
Atom
The smallest part of an element that can exist as a
stable entity.
•
Centrifuging
The separation of the components of a
mixture by rapid spinning. The denser particles are fl ung to
the bottom of the containing tubes. The liquid can then be
decanted off.
•
Chemical change
A permanent change in which a new
substance is formed.
•
Chemical formula
A shorthand method of representing
chemical elements and compounds.
•
Chromatography
A technique employed for the
separation of mixtures of dissolved substances.
•
Colloid
System in which there are two or more phases,
with one (the dispersed phase) distributed in the other (the
continuous phase). One of the phases has particles in the
range 1 to 1000 nm (1 nm = 1
×
10
−9
m).
•
Composite materials
Materials which combine the
properties of two substances in order to get the exact
properties required for a particular job.
•
Compound
A substance formed by the combination of
two or more elements in fi xed proportions.
•
Crystallisation
The process of forming crystals from a
liquid.
•
Decanting
The process of removing a liquid from a solid
which has settled or from an immiscible heavier liquid by
pouring.
•
Diatomic molecule
A molecule containing two atoms, for
example hydrogen, H
2
, and oxygen,O
2
.
•
Distillate
The condensed vapour produced from a mixture
of liquids on distillation.
