Elements, compound and mixture

Modern Classification
• On the basis of its physical state, matter is
classified into solid, liquid and gas.(Physical
Change)
• All these three states exist under normal
temperature and pressure conditions
• The fourth state of matter is Plasma.
• on the basis of its chemical constitution,
matter is classified into element, compound
and mixture.( Chemical change)
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Physical and Chemical Changes
• Physical Change:
• A change of matter in size, shape or
state without any change in identity is called a
physical change
• NO new substance is formed.
• These changes are easily reversible or temporary.
• An example is dissolving salt in water.
• Other examples of physical change include:
melting, boiling, mixing 2 solids or liquids.

• Chemical Change:
• A change of matter that occurs when atoms
link together in a new way, creating a new
substance different from the original
substance.
• A NEW substance is formed.
• These changes are irreversible or permanent.
• The new substance formed will have different
properties compared to its original elements. (E.g.
different melting and different chemical reactions
from the original substance.)

• One can recognize a chemical change from 2
observations:
• The new substance has a different appearance, such as
different color or different physical state.
• An example is the electrolysis of water.
• Reason: Electrolysis of water produces two new
substances, Hydrogen gas and oxygen gas. Hydrogen
and oxygen are both gases but water is a liquid.
• A lot of heat is given out in a chemical changes.
• Chemical changes are called chemical reactions.

Elements, Compounds and Mixtures
“ single, attached, play play…”

Introducing Little Miss
“Element”
Hi! I am Little Miss “Element”
I am PURE SUBSTANCE
I cannot be broken down into any
simpler substance by means of a
chemical reaction* or electricity**!
*Chemical process refers to
chemical reaction or heat
**Electricity refers to electrolysis
I have
got new
friends

Elements
Definition of an element:
An element is a pure substance which
cannot be split up into two or more
simpler substances by chemical means.
Sugar is not an element as it can be
broken down into carbon and water.

Note that an element:
• Consists of only one kind of atom,
• Cannot be broken down into a simpler type of
matter by either physical or chemical means
• Can exist as either atoms (e.g. argon) or
molecules (e.g., nitrogen).
• Cannot possible to obtain a simpler substance
chemically from these elements.
• Can only make more complicated substances
from it.
Elements

- They are arranged in the Periodic Table, classified as metals
and non-metals.
- They may consist of atoms of same element or molecules of
the same element.
Periodic Table

Examples of elements
Is the smallest particle
of an element and has
the same chemical properties
of the element
Is made up of two or more
atoms that are chemically
bonded together
(note: these atoms are of the
SAME element!!)
Hi, I am from the
“Noble gas” family
and I work alone
We same
same!!

Elements- Atoms
Microscopic view of
the atoms of the
element argon (gas
phase).
Consists of only
one kind of
atom

What is an atom?
Examples of models of atoms:
H Na Cl
Hydrogen
atom
Sodium atom Chlorine
atom

Molecules
Very few elements exists as
atoms besides elements such
as helium and neon.
Most elements exist as
molecules.
For example, hydrogen
is H2.
Ozone is O3.

Hydrogen (H2) is a
diatomic molecule.
Ozone (O3) is a
triatomic molecule.
Molecules consisting of a
few atoms are called
polyatomic molecules.

Elements-Molecules
Microscopic view of the
molecules of the
element nitrogen (gas
phase).
Consists of only
one kind of
atom

Examples of molecules (elements)
H H
N N
O
O
O
O O S
SS
S
S
S
S
S

Chemical Symbols of Elements
Chemists use symbols to represent elements.
For example, O represents oxygen while Fe
represents iron.
Element Symbol Element Symbol
Calcium Ca Mercury Hg
Carbon C Neon Ne
Hydrogen H Silicon Si
Iron Fe Sodium Na

Classification of Elements – Metals
and Non-metals
The elements can be classified according to their
various properties.
There are two major groups of elements –
metals and non-metals.
Iron is a metal. Oxygen is a non-metal.
There are some elements called metalloids
which behave like both metals and non-metals.
Metals and non-metals are grouped separately
on the Periodic Table.

Physical Properties metals and non-metals
Property Metals Non-metals
Physical state at room
temperature
Usually solid (occasionally
liquid)
Solid, liquid or gas
Malleability Good Poor – usually soft or
brittle
Ductility Good
Appearance (Solids) Shiny (lustrous) Dull
Melting point Usually high Usually low
Boiling point Usually high Usually low
Density Usually high Usually low
Conductivity (thermal and
electrical)
Good Very poor

ELEMENTS & SYMBOLS
S.No NAME SYMBOL PHYSICA
L STATE
NAME SYMBOL PHYSICAL
STATE
1
2
3
4
5
6
7
8
9
10
Aluminium
Calcium
Copper
Iron
Magnesium
Mercury
Potassium
Sodium
Zinc
Gold
Al
Ca
Cu
Fe
Mg
Hg
K
Na
Zn
Au
Solid
Solid
Solid
Solid
Solid
Liquid
Solid
Solid
Solid
Solid
Argon
Bromine
Carbon
Chlorine
Silicon
Sulphur
Hydrogen
Iodine
Nitrogen
oxygen
Ar
Br
C
Cl
Si
S
H
I
N
O
Gas
Liquid
Solid
Gas
Solid
Solid
Gas
Solid
Gas
Gas
* Physical states are given at room temperature.
METALS NON- METALS
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Introducing Little Miss “Naughty”
Harlow! Hehee!!!
*giggles*
I am also a PURE SUBSTANCE
I am made up of a fixed number of
two or more elements chemically
combined.

Atoms
• Everything in this world is made of billions of atoms.
• The smallest atom known as hydrogen.
• Each atom is represented as a sphere having a diameter of 7 X 10-8 mm.
• Different elements have different diameter and different masses.
• Chemists use shorthand symbols to label the elements and their atoms.
• The symbols consists of 1, 2 or 3 letters.
• For example
1. C - Carbon
2. Cl - Chlorine
• Some symbols seems to have no relations with the name of the element.
For example:
1. Na – Sodium
2. Pb - Lead
• These symbols come from their Latin names.
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Molecules
• The atoms of same elements join together to form a
molecule.
• The small group of atoms are called molecules.
• For example: when the atoms of elements hydrogen, oxygen,
nitrogen, fluorine, chlorine, bromine and iodine are each
joined in pairs and are known as diatomic molecules.
• but in phosphorus and sulfur the atoms are joined in larger
numbers, 4 and 8 respectively (P4, S8)
• The gaseous elements helium, neon, argon, krypton, xenon
and radon are composed of separate and individual atoms.
• When an element exists as separate atoms, then the
molecules are said to be monatomic.
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Compounds
Note that a compound:
• can be broken down into a simpler type of
matter (elements) by chemical means (but not
by physical means),
• has properties that are different from its
component elements, and
• always contains the same ratio of its
component atoms.

A compound is a substance which is made up of two or more
elements chemically combined together.
What is a compound?
- Chemical reactions taking place.
Cu
Qn: Is this a compound?
It only contains one type of
element.
H HIt only contains one type of
element.
H
O
H
O
O
It is not chemically
combined.

So, what is a compound then?
O
HH
Water
N
H
HH
Ammonia gas
Consists of two or more elements
And
They are chemically combined together!

Compounds
Microscopic view of the
molecules of the
compound water (gas
phase). Oxygen atoms
are red and hydrogen
atoms are white.
Hydrogen + Oxygen Water
H2 + O2 2H2O

ELEMENTS
COMPOUNDhydrogen
(colourless gas)
oxygen
(colourless gas)
lighted
splint
heat, light
and
explosion
water
(colourless liquid)
Making compounds fromtheir elements
Example: Making water (picture)
Water
moleculeOxygen
molecule
Hydrogen
molecule
mixture of
hydrogen
and
oxygen
water
Example: Making water (models)
heat,
light and
explosion

Making compounds fromtheir elements
Example: Making Magnesium Oxide compound
Magnesium + Oxygen  Magnesium oxide
elements
compound
+
Silvery-White colourless gas

heat
heat
White
Magnesium + Oxygen → Magnesium oxide
2Mg + O2 → 2MgO

Oxidation
• When the substances are combined with
oxygen they are said to have been oxidised.
This process is Known as oxidation.
• Eg: Hydrogen and Magnesium combine with
Oxygen

Reduction
• It is the opposite of oxidation.
• In this process oxygen is removed instead of
being added.

Redox Reactions.
Oxidation
Reduction

GCSE
Oxidation:
•Gain of oxygen
•Loss of electrons
Reduction:
•Loss of oxygen
•Gain of electrons
Increase in
oxidation
number
Decrease in
oxidation
number

Redox reaction
Example
• Removing Oxygen in the extraction of iron from
iron(III)oxide
• This can be done in a blast furnace with carbon monoxide.
• The iron(III)oxide loses oxygen to the carbon monoxide and
is reduced to iron.
• Carbon Monoxide is the reducing agent.
• Carbon monoxide is oxidised to carbon dioxide by the
iron(III)oxide.
• The iron(III)oxide is the oxidising agent.
• iron(III)oxide + carbon iron + Carbon dioxide
• Both reduction and oxidation have taken place in this
chemical process, and so this is known as a redox reaction.
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Reducing Agent
• A reducing agent is a substance that reduces
another substance during a redox reaction
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Oxidising Agent
• An oxidising agent is a substance which
oxidises another substance during redox
reaction.
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Little Miss “Naughty”
Property #1
I can be represented as
a “chemical formula”
The different elements
present in a compound
are combined in a fixed
ratio
General Rules:
- Only write the name of the metallic element
first
- Write the number of atoms of any element
in the compound in subscript
(applies to only 2 or more atoms)
- “ide” will always be written at the
end of the non metal element
Special Rules:
• Does not apply to organic compounds
(chapter 18 onwards)

Property #2
I am formed by atoms
of different elements.
However, I do not have
the properties as them.
Examples
• Na + Cl2  NaCl
(s) (g) (s)
• H2 + O2  H2O
(g) (g) (l)

Property #3
Because of my chemical bonds, I
cannot be broken down by physical
means. I can only be broken down
by chemical reaction or electricity.
Electrolysis
(breaking down of compound by electricity)
2MgCl(s)  Mg(s) +Cl2(g)
Thermal Decomposition
(breaking down of compound by heat)
HgO(s)  Hg(s) + O2(g)

How do we name compounds?
Rule 1
A compound made up of two elements
has a name that ends in -ide.
• Sodium chloride — made up of the elements
sodium and chlorine
• Zinc oxide — made up of the elements zinc and
oxygen
• Carbon dioxide — made up of the elements
carbon and oxygen

Rule 2
A compound that contains hydroxide ions , OH–
(a negatively charged ion made up of oxygen
and hydrogen) is named a hydroxide.
• Potassium hydroxide — contains potassium ions
and hydroxide ions

Rule 3
A compound that contains a negatively
charged polyatomic ion containing oxygen
usually has a name ending in –ate.
• Copper(II) sulphate — contains oxygen atoms in
the sulphate ion
• Sodium nitrate — contains oxygen atoms in the
nitrate ion

Fixed Composition of Compounds
For example, water (H2O) is a compound made
only by joining together two atoms of hydrogen
to one atom of oxygen.
That is, the ratio of hydrogen atoms to oxygen
atoms in water is always 2 : 1.
A compound is made up of different elements
chemically combined in a fixed ratio.

Copyright © 2006-2011 Marshall
Cavendish International (Singapore)
Pte. Ltd.
Chemical Formula of a Compound
A compound can be represented by a chemical
formula.
The chemical formula states
• the types of atoms (i.e. elements) in the
compound,
• the ratio of the different atoms in the
compound.
Types of atoms:
hydrogen, oxygen
Ratio of H to O = 2:1

How do we write chemical formula?
Rule 1
For many compounds that contain both
metallic and non-metallic elements, the
symbol of the metallic element is written
first.
• calcium oxide (CaO)
• sodium chloride (NaCl)
• magnesium carbonate (MgCO3)

Rule 2
The number of atoms is written as a
subscript, to the right of the atom’s symbol.
• water (H2O, not H2O or 2HO)
• magnesium carbonate
(MgCO3, not MgCO3 or MgC3O)

Rule 3
It is not necessary to write the
subscript ‘1’.
• water (H2O, not H2O1)
• calcium oxide (CaO, not Ca1O1)

Rule 4
The oxygen atom is usually written at
the end of the formula.
• water (H2O, not OH2)
• carbon dioxide (CO2, not O2C)
• nitric acid (HNO3, not O3NH)

How do we calculate the number of
atoms in a formula?
Pb(NO3)2
Number of nitrogen (N) atoms
= 1 x 2 = 2Number of lead (Pb) atoms = 1
Number of oxygen (O) atoms
= 3 x 2 = 6

Heat can be used to break down compounds
into elements or simpler compounds. Such a
chemical reaction is called thermal
decomposition.
Compounds can be Decomposed
Mercury(II) oxide
Oxygen

Summarizing
• A compound is made up of two or more
elements chemically joined together
• A compound has a fixed composition
• Every compound has a unique chemical
formula
• A compound has a completely different
properties from its elements
• A chemical reaction (decomposition or
electrolysis) is needed to separate the
elements in the compound

N N O O
S
S
S
S
S
S
S
S
OH H
O O
C N
H
HH

Balancing chemical equations
• Word equations are used to represent
chemical reactions.
• But better and more useful method is to
produce a balanced chemical equation.
• This type of equation gives the formulae of
the reactants and the products.
• And also it shows the relative numbers of each
particle involved.
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Law of Conservation of Mass
You need to remember this law!
• The Law of Conservation of Mass states: that
mass is neither created nor destroyed in any
chemical reaction. Therefore balancing of
equations requires the same number of atoms
on both sides of a chemical reaction.
• The number of atoms in the Reactants must
equal the Number of atoms in the Products

Law of Conservation of Mass
• The mass of all the reactants (the substances
going into a reaction) must equal the mass of
the products (the substances produced by the
reaction).
• Reactant + Reactant = Product

Steps to Balancing a Chemical Equation
1. Write all reactants
on the left and all
products on the
right side of the
equation arrow.
Make sure you write
the correct formula
for each element
2. Use coefficients in front
of each formula to
balance the number of
atoms on each side.

Steps to Balancing a Chemical Equation
3. Multiply the coefficient
of each element by the
subscript of the
element to count the
atoms. Then list the
number of atoms of
each element on each
side.
4. It is often easiest to start
balancing with an element
that appears only once on
each side of the arrow.
These elements must have
the same coefficient. Next
balance elements that
appear only once on each
side but have different
numbers of atoms. Finally
balance elements that are in
two formulas in the same
side.

A simple equation, such as the synthesis of
Iron (II) sulfide
• iron + sulfur Iron (II) sulfide
• Replace the words with symbols for the reactants
and products.
• Fe + S FeS
• Note that in a chemical equation, by convention,
we use the arrow “ " instead of the equals “ =
".
• There is same number of each type of atom on
both sides of the equation. So this is the balanced
chemical equation.

• The last stage is to put in state of matter
symbols, (s, l, g, aq), as appropriate (solid,
liquid, gas, aqueous or dissolved in water)
• Fe(s) + S(s) heat FeS(s)
A simple equation, such as the synthesis of
Iron (II) sulfide

Re-cap of steps from rule 4:
• Balance elements that appear only once on
each side of the arrow.
• Next balance elements that appear only once
on each side but have different numbers of
atoms.
• Finally balance elements that are in two
formulas in the same side.

First you need an equation with the correct “formulae”
………. You’ll probably be given this in the question
Just like this one
Mg + O2  MgO
Then all you do is list the atoms that are involved
on each side of the arrow
Mg + O2  MgO
Mg
O
Mg
O

[1] Just count up the atoms on each side
Then start balancing:
Mg + O2  MgO
Mg
O
1
1
1
2
[2] The numbers aren’t balanced so then add “BIG”
numbers to make up for any shortages
And adjust totals
Mg + O2  MgO
Mg
O
1
1
1
2
2
2
2

Mg + O2  MgO
Mg
O
1
2
2
2
2
But the numbers still aren’t equal, so add
another “BIG” number
2
And adjust totals again
NOW BOTH SIDES HAVE EQUAL
NUMBERS OF ATOMS
WE SAY THAT THE
EQUATION IS BALANCED!!
2

Try to balance these equations using the same
method:
[1] Na + Cl2  NaCl
[2] CH4 + O2  CO2 + H2O
[4] Al + O2 Al2O3
[3] Li + HNO3  LiNO3 + H2

How did you get on??
[1] 2 Na + Cl2  2 NaCl
[2] CH4 + 2 O2  CO2 + 2 H2O
[4] 4 Al + 3 O2  2 Al2O3
[3] 2 Li + 2 HNO3  2 LiNO3 + H2
Here are the answers:

Instrumental techniques
Modern chemists use a range of instruments to analyse and identify substances. Most
produce quantitative data, which requires expert interpretation.
There are many different types of machine used for analysis, each producing a different
type of information, such as:
 whether a substance is pure or a mixture
 the molecular mass of a compound
 the types of bonds in a molecule
 the arrangement of atoms in a molecule
 the isotopes of different atoms in a substance.

Instrumental techniques
• Many instrumental methods are developed.
• Some methods are suited for identifying
elements.
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Atomic absorption spectroscopy
Atomic absorption spectroscopy (ABS) is a technique that allows elements to be
identified, and their concentration measured down to just a few parts per billion.
ABS has many uses:
 environmental chemistry – to analyse pollutant
concentrations in air and water
 medicine – to analyse concentrations of toxic chemicals in
blood and urine
 building – to check for impurities in concrete and steel
 mining – to check how much
metal is in an ore.

• Some methods are suited to the identification
of compounds
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Infrared Spectroscopy
• This is used to identify the compounds by
showing the presence of particular groupings of
atoms.
• This is used in Pharmaceutical industries to
identify and discriminate between drugs that are
similar in structure.
• Eg: Penicillin type drugs.
• Used to identify both organic and inorganic
molecules.
• Samples can be solid, liquid or gas.
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Infrared Spectroscopy
• This is used to monitor environmental
pollution.
• It has biological uses in monitoring tissue
physiology including
• Oxygenation,
• Respiratory status
• Blood flow damage
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Instrumental Techniques
• Forensic scientists used this methods because
• They are very accurate
• They require tiny amounts of sample
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• Other techniques utilised are nuclear magnetic
resonance spectroscopy and Ultraviolet/
Visible Spectroscopy

Think about this…Yummy
Pickle

Introducing Little Mr. “Mixture”
Burp!!!! I am messy!
I am formed when two or more substances joined
together physically (without chemical bonds)
I have the same properties as all the substances
AIR
I am his best friend!

Mixtures
Definition of a mixture:
A mixture is not a pure substance as it
contains a mixture of atoms of
molecules which are not chemically
combined together.

Microscopic view of a
gaseous mixture
containing two
elements (argon and
nitrogen) and a
compound (water).
Mixtures

Mixtures
• Examples of mixtures include muddy water
and air.
Air is made up of gases such as nitrogen and
oxygen mixed together.

Little Mr “Mixture”
I do not have a fixed composition of the
substances.
A Mixture can be:
• element + element
• element + compound
• compound + compound
(Refer to page 59, Fig 4.7)
He is a “boo-boo!”
He can be separated to its
substances by physical methods

A mixture of 2 elements
A mixture of two
elements, e.g. neon (Ne)
and hydrogen (H2)

A mixture of 1 element and
1 compound
A mixture of one element
and one compound, e.g.
hydrogen (H2) and
ammonia (NH3)

A mixture of 2 compounds
A mixture of two
compounds, e.g. water
vapour (H2O) and
carbon dioxide (CO2)

CHARACTERISTICS OF MIXTURE
• It is an impure substance
• No formula
• They can be mixed in any ratio.
• The properties of the mixture are the properties of
its constituents.
• Constituents can be easily seperated by physical
methods e.g. heating, drying, crystallization,
distillation etc.
• It is either homogenous or heterogenous.
90،‫جمعه‬10،‫رمضان‬1436

Mixtures
Homogenous mixture
Is the type of mixture that has a completely
uniform composition throughout itself.
It’s components are evenly distributed
throughout the sample.

Homogenous or Heterogenous?
1. Air
2. Salt water
3. Tea
4. Brass
5. Vinegar
6. Hydrogen peroxide
7. Steel
1. Salad dressing
2. Apple
3. Sand
4. Paint
5. Granite
6. Laundry detergent
7. Cereal

Solutions
• Is the special name that scientists give to
homogenous mixtures.
• Solutions may be gases, liquids or solids.
• An example: solution of sugar in water.

Solutions
Some common types of solutions
System Examples
Gas-gas CO2 and O in N (air)
Liquid-gas Water vapor in air
Gas-liquid CO2 in H2O (Soda water)
Liquid-liquid Acetic acid in H2O (vinegar)
Solid-liquid NaCl in H2O (brine)
Solid-solid Cu in Ag (Sterling silver)

Phases
• Any part of a system with uniform
composition and properties is called a phase.
• On a homogenous mixture you have “one
phase” only.
• On a heterogenous mixture you have “two or
more phases”.

Phases in a heterogenous mixture

Phases in a homogenous mixture

Difference between Mixtures and Compounds
Example
• A mixture of iron fillings and sulphur looks
different from the individual elements.
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• This mixture has the
properties of both
iron and sulfur.
• A magnet can be used to
separate the iron
fillings from the sulfur

Example
• This mixture has the properties of both iron
and sulfur.
• A magnet can be used to separate the iron
fillings from the sulfur.
• Substances in a mixture have not undergone a
chemical reaction.
• It is possible to separate them by using their
physical properties.
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• If the mixture of iron and sulfur is heated a
chemical reaction occurs and a new substance
is formed called iron (II) sulfide.
• Iron + Sulfur iron (II) sulfide.
• iron (II) sulfide has different properties to the
mixture of iron and sulfur.
• This iron (II) sulfide would not be attracted
towards a magnet.
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Example
heatt

Different properties of iron, sulfur, an iron/sulfur
mixture and iron (II) sulfide
Substance Appearance Effect of a magnet Effect of dilute HCl
Iron Dark grey
powder
Attracted to it Very little action
when cold. When
warm, a gas is
produced with a lot of
bubbling
Sulfur Yellow powder None No effect when hot or
cold
Iron/Sulfur mixture Dirty yellow
powder
Iron powder
attracted to it
Iron powder reacts as
above
iron (II) sulfide Black solid No effect A foul-smelling gas is
produced
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Differences between mixtures and
compounds
*giggles*
HeE
stupid…
Laugh what? I
know I am a little
“bushy and hairy”
than you…
Little Miss CompoundMr Messy

EXTRA!
• Human body is made up of 28 elements?
• About 99% our mass is made up of the 6
main elements
– Oxygen (65%)
– Carbon (18%)
– Hydrogen (10%)
– Nitrogen(3%)
– Calcium (1.5%)
– Phosphorus (1.5%)

Seperating Solid Mixtures
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Suppose you had a mixture of iron nails, salt
and water…
How would you separate this mixture
completely?
Based on which physical properties would you
base your method on?

Distillation
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How would you separate the components in
tap water?
Distillation
A liquid is boiled to produce vapor that is
then condensed again to a liquid

Distillation Process
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Seperating Solid/Liquid mixtures
• Sedimentation and Decantation
• Sedimentation is the process of separating an
insoluble solid from a liquid in which it is
suspended by allowing it to settle to the
bottom of the container. If this also involves
pouring off of the liquid leaving the solid
behind, it is called decantation.
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Crystallisation
Crystallisation is a sophisticated form of evaporation technique
in which crystals of the solute are encouraged to develop during
the process of “dissolving out” from the solution as the solvent
evaporates.
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Evaporation
Evaporation is used for recovering dissolved solid
substances from solutions by evaporating the solvent.
The solute “dissolves out” and is left behind.
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Differential Centrifugation
The simplest form of separation by centrifugation is differential
centrifugation, sometimes called differential pelleting (see Figure
1). Particles of different densities or sizes in a suspension will
sediment at different rates, with the larger and denser particles
sedimenting faster. These sedimentation rates can be increased by
using centrifugal force. A suspension of cells subjected to a series
of increasing centrifugal force cycles will yield a series of pellets
containing cells of decreasing sedimentation rate.

Seperating Liquid Mixtures
Liquids are divided into two:
Miscible Liquids
Immiscible Liquids
Definition of Miscible liquids:
Miscible Liquids are formed when when two
substances mix together completely.
For example: Apple juice and Pineapple Juice.
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Immiscible Liquids:
Immiscible liquids are formed. two substances
do not mix together and form a different layer
for
Ex: Oil and water.
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Fractional Distillation
Fractional distillation is the process of separating two or more miscible liquids by a
modified distillation process, in which the distillates are collected as fractions having
different boiling points. The separation of the liquids by this method is based on the
difference in their boiling points. (Fig. 5)
Fractional distillation makes use of a fractionating column or distillation
column, a tube which provides different temperature zones inside it during distillation,
the temperature decreasing from bottom to top. It provides surfaces on which
condensations (of less volatile liquids) and vaporizations (of more volatile liquids)
can occur before the vapours enter the condenser in order to concentrate the more
volatile liquid in the first fractions and the less volatile components in the later fractions.
Fractional distillation is very effective is separating mixtures of volatile components, and
is widely used in laboratories and industries.

Filtration
Filtration is used for separating
insoluble solids from a liquid.
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Chromatography
When we separate two or more solids that are
soluble. This type of problem is encountered
when you have mixtures of coloured materials
such as inks and dyes.A technique called
chromotography is widely used to separate these
materials so that they can be identified.
There are several types of chromatography,
however they all follow the same basic principles
the simplest kind is paper chromotography. To
separate the different coloured dyes in a sample
of black ink, a spot of the ink is put on to a piece
of chromatography paper. This paper is then set
in a suitable solvent.6/26/2015

Chromotography
As the solvent moves up the paper the dyes are
carried with it and begin to separate. They
separate because the substance have different
solubilities in the solvent and are absorbed to
different degrees by the chromotography
paper as they result they are seperated
gradually as the solvent moves up the paper.
The chromotogram shows how the ink
contains three dyes.
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Solvent Extraction
Sugarcan be obtained from crushed sugar cane
by adding water. The water dissolves the sugar
from the sugarcane. This is an example of
solvent extraction. In a similar way some of
the green substances can be removed from
ground - up grass using ethanol. The
substances are extracted from the mixtures by
using a solvent which dissolves only those
substances required.
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Criteria for purity
Drugs are manufactured to very high degree of
purity. To ensure that the highest possible purity
is obtained the drugs are dissolved in a suitable
solvent and subjected to fractional crystallisation.
It is illegal to put anything harmful into a food. Also
government legislation requires that a lot of
testing takes place before a new pharmaceutical
is marketed.
Throughout the chemical, pharmaceutical and food
industries it is essential that the substance used
are pure. The purity of a substance can be gauged
by:6/26/2015

Criteria for purity
• Its melting point – if it is a pure solid it will have a
sharp melting point. If an impurity is present then
the melting point takes over a range of temperature
• Its boiling point – if it is a pure liquid the
temperature will remain steady at its boiling point.
If the substance is pure then the mixture will boil
over a temperature range.
• Chromotography – if it is a pure substance it will
produce only one well defined spot on a
chromatogram. If impurities are present then
several spots will be seen the chromotogram.
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Conclusion
An element is a pure substance which cannot be split up
into two or more simpler substances by chemical
means.
A compound consist of a fixed number of different kinds
of atoms chemically combined together.
A mixture is not a pure substance as it contains a
mixture of atoms of molecules which are not
chemically combined together.

Elements, compound and mixture

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