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C1 Nature of matter and C2 Experimental techniques (Shi Yu) (Methods of…
C1 Nature of matter and C2 Experimental techniques (Shi Yu)
Diffusion
: Diffusion occurs when particles
spread
. They move from a region where they are in
high
concentration to a region where they are in
low
concentration.Diffusion happens when the particles are free to
move
. The higher the
molecular mass
, the slower the diffusion
Measurement and apparatus
Electronic balance
Mass(g)
Measuring cylinder
Volume of liquid(cm3)
Thermometer
Temperature(0C)
Burette
Volume(cm3)
Stopwatch
Time(second)
Pipette
Volume(cm3)
Density = Mass / Volume
Criteria of purity
Does purity matter?
:
Often it does not matter if a substance is not pure. We wash in tap water, without thinking too much about what is in it. But sometimes purity is very important. If you are making a new
medical drugs
, or a flavouring for
food
, you must make sure it contains nothing that could harm people. An unwanted substance, mixed with the substance you want, is called an
impurity
.
How can you tell if a substance is pure?
:
A pure substance has a
definite, sharp
, melting point and boiling point. When a substance contains an impurity:
1.its melting point
falls
and its boiling point
rises
.
2.it melts and boils
over a range
of temperatures, not
sharply
Methods of purification
A pure substance
has no particles of any other substance mixed with it.
Method of separation, and used to separate ...
Filtration : a solid from a liquid
Evaporation : a solute from a solution
Crystallisation : a solute from a solution
Simple distillation : a solvent from a solution
Fractional distillation : liquid from each other
Solvent extraction : two immisible liquids
Paper chromatography : mixture of colors
Filtration
: Filtration separates a
solid
from a
liquid
. (Example – separating sand from water.)
Evaporation
: If the substance is flammable, heat it using a
water bath.
Crystallisation
: Crystallisation obtains solids from their solutions by letting crystals form. It works because soluble solids tend to be
less soluble
at lower temperature. (Example – to obtain pure solid copper(II) sulfate from a solution of copper(II) sulfate) A saturated solution
can hold no more solute
at that temperature.
Simple distillation
: Simple distillation obtains the
solvent
from a solution. (Example – to obtain water from sea water)
Fractional distillation
: Fractional distillation separates
a mixture of liquids
from each other. (Example – 1. to separate ethanol and water; 2. to separate various fractions from petroleum; 3. to separate different gases from liquid air)
Solvent extraction
: Mixtures of two
immiscible
liquids can be separated if the mixture is placed in a
separating
funnel
and allowed to stand. The liquids separate into different
layers
.
(Example – to separate the oil and water)
Paper chromatography
: Paper chromatography can be used to separate a mixture of two or more
dissolved
substances. (Example - to find out how many different dyes there are in black ink).
Important points for paper chromatography:
1.The base line must be drawn using
pencil
, if not, the line can also be moved by the solvent.
2.When dip the paper in the solvent, the level of the solvent must start
below
the sample. Otherwise, the sample will
dissolve
in the solvent directly rather than move up with the solvent.
3.A
locating agent
is used to produce colored spots for the colorless sample.
4.The retention factor (Rf value) is used to identify the substance.
Rf = distance moved by the substance / distance moved by the solvent front
Three states and change of states
Liquid
Particle
arrangement
Random
Particle
movement
Flow easily
Gas
Particle
arrangement
Very random
Particle
movement
Move easily
Solid
Particle
movement
vibrate on its position
Particle
arrangement
Regular
Solid-->(
melting
)-->Liquid-->(
boiling
)-->Gas
Gas-->(
condensation
)-->Liquid-->(
freezing
)-->Solid