C1 Nature of matter and C2 Experimental techniques (Shi Yu) (Methods of…
C1 Nature of matter and C2 Experimental techniques (Shi Yu)
: Diffusion occurs when particles
. They move from a region where they are in
concentration to a region where they are in
concentration.Diffusion happens when the particles are free to
. The higher the
, the slower the diffusion
Measurement and apparatus
Volume of liquid(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
, or a flavouring for
, you must make sure it contains nothing that could harm people. An unwanted substance, mixed with the substance you want, is called an
How can you tell if a substance is pure?
A pure substance has a
, melting point and boiling point. When a substance contains an impurity:
1.its melting point
and its boiling point
2.it melts and boils
over a range
of temperatures, not
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 separates a
. (Example – separating sand from water.)
: If the substance is flammable, heat it using a
: Crystallisation obtains solids from their solutions by letting crystals form. It works because soluble solids tend to be
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 obtains the
from a solution. (Example – to obtain water from sea water)
: 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)
: Mixtures of two
liquids can be separated if the mixture is placed in a
and allowed to stand. The liquids separate into different
(Example – to separate the oil and water)
: Paper chromatography can be used to separate a mixture of two or more
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
, 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
the sample. Otherwise, the sample will
in the solvent directly rather than move up with the solvent.
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
vibrate on its position