PURE SUBSTANCES AND MIXTURES
1. PURE AND MIXED SUBSTANCES.
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A pure substance is a kind of matter that cannot be separated into other kinds of matter by
any physical process. It is made of a same particle. Examples are: water (H2O), iron ( Fe ) , etc...
There are two types of pure substances: simple substance and compounds.
a) Simple substances or elements. They are made of only kind of an atom, such us
carbon ( C), oxygen (O2 ), iron, gold...
b) Compounds. They are made of two or more different atoms ( elements) that can
be separated into simpler substances by chemical methods ( chemical reactions ).
Examples are water ( H2O), carbon dioxide ( CO2 ), sodium clorhide (NaCl),...
A mixture is a material system made up by two or more different substances which are
mixed together but are not combined chemically. It can be separated by physical methods.
There are two types of mixtures: heterogeneous and homogeneous.
a) A heterogeneous mixture is a type of mixture in which the components can
easily be identified, as there are two or more phases present. The substances can be
distinguished easily. Example: Granite.
b) A homogeneous mixture ( solutions ) is a type of mixture in which the
composition is uniform. The substances cannot be distinguished easily. Examples:
air, sea water.
An alloy is a metallic solid solution composed of two or more elements.
Example: Steel, bronze,etc...
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Characteristic properties of compounds are different from those of their constituent
elements and compounds have specific and constant (invariant) properties that allow to identify
them.
Mixture's properties are closely related of its related of its constituents, so they are variable
and they depend on its constituents.
Activity 1. Classify the following substances:
Agua, granito, clavo de hierro, whisky, agua de mar, acero, mercurio, oro, aire, amoniaco,
agua con tierra, vino, butano , oxígeno.
SUSTANCIA PURA
ELEMENTO
MEZCLA
COMPUESTO
HOMOGÉNEA
HETEROGÉNEA
Water
Activity 2. Match the following words:
Gasoline
Element
Water
Homogeneous mixture
Gold
Heterogeneous mixture
Water with sand
Compound
Activity 3. Which of the following metallic materials are pure substances?
SUBSTANCE
Gold
( Au)
Mercury ( Hg )
Steel
Iron
( Fe )
Lead
( Pb)
Bronze
Copper
Latón
2
( Cu)
( Cu + Zn)
PURE SUBSTANCE
ALEACIÓN ( Disolución)
Activity 4. Indicate which material is a mixture, which an element and which a compound.
Activity 5. Indicate which of the following systems are heterogeneous and homogeneous: Granite,
an iron nail, wine, basket full of clothes, ink, water, sea, air, water with soil, stew (cocido) and ice
water.
HOMOGENOUS
HETEROGENOUS
Activity 6. Indicate which substances are in the following mixtures: ( Look up the information on
internet if you need it) .
MIXTURE
SUBSTANCES
MIXTURE
Sea water
Water and salt
Granite
Milk
Blood
Air
Anticongelante coche
Acero
Bronce
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SUBSTANCES
2. SEPARATING MIXTURES.
Physical processes are used to separate substances.
There are several methods.
2.1. Separation of substances in a heterogeneous mixture
METHOD
BASED ON
SEPARATE
Imantación
Difference in magnetic properties.
Metals and other substances.
Metal remains stuck to the magnet
Ej: Iron and sand
Difference in size.
Two solids.
Tamizado
The larger solid substance remains in the sieve Ex: Stones and sand.
and the small passes through.
Filtración
Difference in size.
Solid and liquid.
Ex: Sand and water.
The solid substance remains on the filter and
the liquid passes through
Sedimentación
Difference in density.
Solids or solid and liquid.
Two substances are separated by the action of
gravity, the denser one goes down and less Ex: Sand and water.
dense goes up. It's slow and cheap.
Decantación
Difference in density.
Two immiscible liquids are separated by the
action of gravity, the denser one goes down
and less dense goes up. It's slow and cheap.
Centrifugación
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Two immiscible liquids
(cannot
mix).
Ex: Water and oil
Difference in density.
Solids , solid and liquid or liquids.
Two substances are separated by the action of
an acceleration ( much bigger than gravity)
Ex: Water and clothes
It's fast and expensive.
.
2.2. Separation of substances in a homogeneous mixture ( solution )
METHOD
BASED ON
SEPARATE
Evaporación
Difference in boiling point.
A solid and a liquid.
Artificial heating of a solution. The liquid Ex: water and salt
evaporates and the solid substance remains.
Fast and expensive.
It can destroy some sensible substances such as
vitamin C.
Cristalización
Difference in boiling point.
A solid and a liquid.
Natural warming (Sun) of a solution. The
liquid evaporates and the solid remains.
Ex: Water and salt
Slow and cheap.
It does not destroy sensible substances.
Destilación
Difference in boiling point.
Miscible liquids (or gases
).
Artificial heating of a solution. The most Ex: Water and alcohol.
volatile liquid evaporates and the other liquid
remains.
Recovery of gas by cooling.
Extracción
Different solubility in two immiscible
solvents.
Substances are not destroyed by heat, but is
more expensive than distillation.
Its performance is bigger than distillation.
Any substance dissolved in another.
Example: Iodine dissolved in water is
extracted with CCl4 that is immiscible
in water.
Cromatografía
Difference in speed of the particles through
a porous medium.
Any substance dissolved in another.
Example: Separate pigments (colours)
plants, or ink components.
The mixture is passed through a porous
medium and the substances are separated by
their difference in speed.
Activity 7. Indicate the most suitable method to separate the components of these mixtures (It may
be more than one method):
MIXTURE
Agua con barro fino
Leche y nata
Sand and stones
Clavos y arena fina
Oil and water
Arena y agua
Sea water
Whisky
Ink
Water and Vitamin C
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METHOD 1
METHOD 2
Activity 8. Match the following words:
Criba, tamizado
Destilación
Size
Decantación
Separación magnéticas
Ferromagnetismo ( imanes)
Sedimentación
Cristalización
Density
Filtración
Cromatografía
Boiling point
Centrifugación
Extracción
Solubility
Evaporación
Speed
3. SOLUTIONS.
A solution is a homogeneous mixture of two or more substances. A solution has two parts:
Solvent: A substance in which other substance or substances are dissolved.
Solutes: The substances dissolved in a solvent are called solutes.
SOLUTO
SOLUTO
DISOLVENTE
DISOLVENTE
DISOLUCIÓN
DISOLUCIÓN
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Concentration : It is the abundance of a constituent divided by the total volume of a
mixture. There are several methods to express the relative amounts of the components of a mixture.
3.1 Percent composition ( by mass ) . It express the concentration as a percentage of solute
to the mass of the entire mixture.
% masa de soluto=
ms
∗100
m
Some solutions are so dilute, that it is more convenient to use parts per million ( ppm), or
even parts per billion ( ppb) , instead of percent ( parts per one hundred ).
Example:
458 ppm =
458g
∗ 100 = 0,0458%
1.106 g
3.2 Percent composition ( by volume) ( . It express the concentration as a percentage to the
volume of the entire mixture.
% volumen de soluto=
Vs
∗100
V
1.3. Mass concentration ( C ). It is defined as the mass of solute ms divided by the volume
of the micture ( V) .
C=
ms
V
DANGER , BE CAREFULL. Do not confuse concentration with density.
d=
m
V
4. SOLUBILITY.
Solubility is a maximum amount of solute that dissolves in a solvent.
Some substances, like water and alcohol, can be mixed together and create a homogenous
phase in any proportion. A solubility measure cannot be applied to such two substances. Such
substances are called miscible. On the other hand if two substances cannot be mixed together (like
water and oil), they are called immiscible.
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4.1. Factors affecting solubility:
a) Temperature: Usually, solubility increases with temperature . The situation is
though different for gases and calcium and magnesium salts ( cal del agua). With increase of the
temperature they become less soluble in water.
b) Polarity: In most cases solutes dissolve in solvents that have a similar polarity.
Nonpolar solutes do not dissolve in polar solvents and viceversa.
c) Pressure: It only affects to gasses. The solubility of gas is directly proportional to
the pressure .
d) Stirring: It does not have an affect on solubility of a substance. Stirring only
increases the speed of the process. Stirring decreases solubility in gases because gases can escape
easier from solution.
There are several types of solutions:
Diluted. The concentration of a solute is very low.
Concentrated: The concentration of a solute is high. It has a very large amount of the solute
in solution.
Saturated: A solution cannot dissolve more solute. It is depend on the temperature.
Supersaturated: The concentration is higher than the saturation point. It is a metastable and
unstable situation.
LINKS
1) http://www.solubilityofthings.com/basics
2) http://www.sciencegeek.net/Chemistry/taters/solubility.htm
3) http://www.hometrainingtools.com/chemicals-a-c/c/68/
4) http://www.chemprofessor.com/conc.htm
5) http://www.youtube.com/watch?v=SMjX5eXnK5Q
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