Download CLASSIFICATION OF MATTER

UNIT 2
CLASSIFICATION OF
MATTER
QUÍMICA
1 BATXILLERAT
Homogeneous matter and heterogeneous matter
Homogeneous matter is that whose constituents cannot be distinguished with the
naked eye nor with a conventional microscope. It has a uniform distribution of particles
and, at any point in the matter, the composition and properties are the same.
Heterogeneous matter is that whose constituents can be distinguished with the naked
eye or with a microscope. The distribution of particles is usually non-uniform. In
consequence, the composition is not usually the same across all points.
Pure substances
A pure substance is one that is formed by a single phase of uniform and invariable
composition.
The purity of a substance can be determined from its heating curve.
Heating curve of a pure
substance
Heating curve of an impure
substance
Elements (I)
The elements are pure substances with a single type of atom; they cannot be broken
down into simpler substances by chemical procedures. For example: carbon, iron,
aluminium, etc.
Arrangement of the elements
118 elements are known.
They are arranged according to atomic number in the periodic table.
Various numbers can be placed around the symbol of a given element:
Classification of the elements
The elements can be classified into:
Metals.
Non-metals.
Noble gases.
Elements (II)
Classification of the elements
According to the
number of atoms that
form the molecule
Monoatomic.
Diatomic.
Polyatomic.
Giant crystalline structures.
Ions
When an atom of any elements loses or gains electrons, it becomes a
charged particle called an ion.
Types of ion
Anion: gains electrons and has a negative charge.
Cation: loses electrons and has a positive charge.
Compounds
Compounds are substances formed by atoms of two or more elements
combined in a definite and invariable proportion.
Characteristics of compounds:
They are represented by formulae with the symbols of the elements that make them
up and with subscripts.
They can be broken down into simpler substances through chemical procedures.
Examples:
Molecule of water:
Molecule of hydrogen peroxide:
H20
H2O2
Mixtures
Mixtures are combinations of various pure substances without chemical interaction.
Characteristics of mixtures:
They retain the properties of the original substances.
They can be broken down into simpler substances through physical procedures.
Homogeneous mixtures are formed by different components, while still having a
uniform distribution of homogeneous matter.
For example: sea water, commercial vinegar or air.
In heterogeneous mixtures the distribution of the particles is not uniform; in
consequence, the composition is not the same at all points.
For example: the mixture of sulphur and iron filings.
Solutions (I)
Solutions are homogeneous mixtures of two or more substances.
In a homogeneous mixture of two compounds, we have:
Solution = solute + solvent
Solute: the substance that is dissolved.
Solvent: the substance that dissolves the solute.
In the majority of solution that are found in everyday life, the solvent is water. Some other
possibilities are:
Solubility
The solubility is the quantity of solute dissolved in a given quantity of solvent
in a saturated solution.
The solubility depends on the temperature.
Types of
solution
Dilute: contains a small proportion of solute.
Concentrated: contains a large proportion of solute.
Saturated: the solvent will not take any more solute.
Not saturated: the solvent will take more solute.
Supersaturated: contains more dissolved solute than corresponds to saturation.
Solubility curves are graphs that
show the quantity of solute that can
dissolve in a given quantity of solvent
as a function of temperature.
Separation of the components of heterogeneous mixtures (I)
Filtration
Filtration is a technique that allows the separation of solid–liquid heterogeneous
mixtures by filters, based on the different size of the particles.
The liquid can pass through the filter, which retains the particles of the solid.
Characteristics of decantation:
When carried out industrially, sand, press, band, disc
and drum filter, etc. are used.
When carried out in the laboratory, funnels and filter
paper are used.
Drum filter
Sand filter
Separation of the components of heterogeneous mixtures (II)
Filtration
Characteristics of filtration:
Filtration can be accelerated with a vacuum, and also with pressure.
Vacuum filtration with a Büchner
funnel and a Kitasato flask
Filtration at atmospheric
pressure
Separation of the components of heterogeneous mixtures (III)
Decantation
Decantation is a technique based on a difference in
densities, and is used when the components to be
separated are very different with respect to this quantity.
Characteristics of decantation:
It can be used to separate two immiscible liquids: a
laboratory separating funnel is used.
It can be used to separate solids and liquids.
Sedimentation and centrifugation
Sedimentation allows the separation of
solids from a solid–liquid heterogeneous
mixture based on the difference in
densities.
Separating funnel
Centrifugation consists of applying a highspeed rotation to the mixture to be
separated. This makes the denser particles
move away from the axis of rotation, with the
less dense liquid remaining near the centre.
Separation of the components of homogeneous mixtures (I)
Evaporation and crystallisation
Evaporation is a separation technique that consists of totally or partially eliminating the
undesired volatile components of a liquid mixture through the vaporisation of all or part
of the liquid.
This can be achieved by:
Evaporation at atmospheric pressure: for example, salt produced by the evaporation of
sea water.
Evaporation at reduced pressure: for example, the production of concentrated caustic
soda solution.
Crystallisation is an operation that
allows the separation of a solid solute
that is dissolved in a liquid, through
the formation of crystals of the solid
by vaporisation of the liquid.
Separation of the components of homogeneous mixtures (II)
Distillation
This can be achieved by:
Simple distillation: using simple
laboratory distillation apparatus or a
rotavapor.
Fractional distillation: incorporates
a fractionating column.
Separation of the components of homogeneous mixtures (III)
Chromatography
Chromatography is a separation method based on the distribution of the components
of a mixture between two phases: a medium or support (stationary phase), and a solvent
or eluant (mobile phase) that passes through the stationary phase.
In the laboratory it is used, for example, to isolate and analyse substances in very
small quantities.
In industry, to separate organic products such as vitamins, hormones, etc.
Liquid-liquid extraction
Liquid-liquid extraction is a separation method that allows the separation of two liquid
components by the addition of a third component. For this to be possible, the following
must be fulfilled:
AB (homogeneous mixture) + C (soluble to a different degree in A and in B)
BC + AC
Example:
Separation of the components of homogeneous mixtures (IV)
Solid-liquid extraction
Solid-liquid extraction, percolation, leaching or washing is an operation allows the
separation of a component of a homogeneous solid mixture by adding a suitable liquid
solvent. For this to be possible, the following must be fulfilled:
AB (mixture) + C (solvent)
AC + B
Examples:
In the laboratory, solid-liquid extraction is carried out using
apparatus called a Soxhlet.
Soxhlet extractor
Treatment of industrial raw materials (I)
Treatment of solid materials
Grinding: crushers and mills.
Sieving: drum sieve.
Concentration by flotation: floatation cell.
Treatment of industrial raw materials (II)
Treatment of liquid materials and suspensions
Filtration: sand filters, drum filter,
band filters, press filters, etc.
Solid-liquid extraction.
Press filter
Decantation and centrifugation.
Crystallisation.
Liquid-liquid extraction.
Adsorption, chromatography, etc.
Treatment of industrial raw materials (III)
Treatment of gaseous materials
Firstly, it is necessary to remove the solid particles in suspension by:
Cyclones.
Filter tubes.
Electrostatic filters.
Afterwards, the following techniques may be used:
Absorption.
Distillation.