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C1 nature of matter and C2 experimental techniques(Ian) (Methods of…
C1 nature of matter and C2 experimental techniques(Ian)
Measurement
themometer
tempo(*c)
stopwatch
time(second)
electronic balance
mass(g)
pipette
volume of liquid(cm^3)
measuring cylinder
volume of liquid(cm^3)
burette
volume of liquid(cm^3)
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.
Three states and change of states
Three states
liquid
It has a fixed volume and no definite shape.(Takes the shape of the container)
Its particle flow easily and arrange randomly.
It is no compressible and have low density.
gas
Its particle move easily and arrange very randomly.
It is compressible and have very low density.
It has no fixed volume:expand to fill the container and no definite shape(Takes the shape of the container)
solid
It has a fixed volume and definite shape.
Its particle vibrate on its position and arrange regular.
It is no compressible and have high density.
Methods of purification
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.
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)
Evaporation
a solute from a solution
If the substance is flammable, heat it using a water bath.
Simple distillation
Simple distillation obtains the solvent from a solution. (Example – to obtain water from sea
water)
Filtration
Filtration separates a solid from a liquid. (Example – separating sand from water.)
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)
The dyes in the ink have different solubilities in water. So they travel across the paper at different
rates. (The most soluble one travels fastest.)That is why they separate into different spots.
The filter paper with the coloured rings is called a chromatogram.
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 an new medical drugs, or a flavouring for food, you must make sure it contains nothing that could harm people.
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:
its melting point falls and its boiling point rises.
it melts and boils over a range of temperatures, not sharply.