Elements, compound and mixture

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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)

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.


An Overview

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

ElementsDefinition 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

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Elements

• There are 118 elements were identified.• 27 of these do not occur in nature and made

artificially by scientists.Eg: Curium and Unnilpentium

• 91 of the elements occur naturally and range from very reactive gases such as Fluorine and Chlorine, to Gold and Platinum,

which are unreactive elements.

Examples of elementsElements are made up of tiny particlesElements can be further classified into two groups:

Is the smallest particle of an element and has

the same chemical propertiesof the element

Is made up of two or moreatoms 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!!

These are elements!Atoms of same element

Cu

copper element

Na

sodium element

He

helium element

Molecules of same element

HHydrogen gas element

O

H

OO

ozone

AtomsAn element is made of tiny particles called atoms.

The word atom comes from the Greek word atomos meaning “unsplittable”.

The atoms of an element is different from that of another element.

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

MoleculesVery 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

OO

O

O O S

SS

SS

S

SS

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 PHYSICAL STATE

NAME SYMBOL PHYSICAL STATE

12345678910

AluminiumCalciumCopper

IronMagnesiu

mMercury

PotassiumSodium

ZincGold

AlCaCuFeMgHgK

NaZnAu

SolidSolidSolidSolidSolidLiquidSolidSolidSolidSolid

ArgonBromineCarbonChlorineSiliconSulphur

HydrogenIodine

Nitrogenoxygen

ArBrCClSiSHINO

GasLiquidSolidGasSolidSolidGasSolidGasGas

* 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 SUBSTANCEI am made up of a fixed number of two or more elements chemically

combined.

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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 example1. C - Carbon2. Cl - Chlorine• Some symbols seems to have no relations with the name of the element. For

example:1. Na – Sodium2. 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.

CompoundsNote 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

HO

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 WaterH2 + O2 2H2O

ELEMENTSCOMPOUNDhydrogen

(colourless gas)

oxygen(colourless

gas)

lighted splint

heat, light and

explosion

water(colourless

liquid)

Making compounds from their elementsExample: Making water (picture)

Water molecule

Oxygen molecule

Hydrogen molecule

mixture of

hydrogen and

oxygen

water

Example: Making water (models)

heat, light and

explosion

Making compounds from their elements

Example: Making Magnesium Oxide compound

Magnesium + Oxygen Magnesium oxide

elementscompound

+

Silvery-White colourless gas

heat

heat

White

+ oxygen → magnesium oxide2Mg + O2 → 2MgO

Magnesium + Oxygen → Magnesium oxide2Mg + 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

GCSEOxidation:•Gain of oxygen

•Loss of electrons

Reduction:•Loss of oxygen

•Gain of electrons

Increase in oxidation

number

Decrease in oxidation

number

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Redox reactionExample

• 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.

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)


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)


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


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


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 CompoundA 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)


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)


It is not necessary to write the subscript ‘1’.

• water (H2O, not H2O1) • calcium oxide (CaO, not Ca1O1)


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

Molecules- Elements or compounds?

• A molecule consists of two or more atoms of the same element, or different elements, that are chemically bound together.

• It can be a molecule of an element • E.g. N2, O2, S8

• It can be molecule of a compound.• H2O, CO2, NH3

N N O OS

SSS

S

S

S S

OH HO O

C NH

HH

Balancing Chemical Equations

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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.

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 MgOMgO

MgO

[1] Just count up the atoms on each side

Then start balancing:

Mg + O2 MgOMg

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 MgOMg

O

1

1

1

2

2

2

2

Mg + O2 MgOMg

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 techniquesModern 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.

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Instrumental techniques

• Many instrumental methods are developed.• Some methods are suited for identifying

elements.

Atomic absorption spectroscopyAtomic 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.

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• 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

• 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

AIRI am his best friend!

MixturesDefinition 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.

Mixtures• Note that a mixture: • consists of two or more different elements and/or

compounds NOT chemically combined.• Can be homogeneous or non-homogeneous • can be separated into its components by physical

means, and • often retains many of the properties of its

components.

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.

90Tuesday, April 18, 2023

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. Air2. Salt water3. Tea4. Brass5. Vinegar6. Hydrogen peroxide7. Steel

1. Salad dressing2. Apple3. Sand4. Paint5. Granite6. Laundry detergent7. 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 airGas-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

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Difference between Mixtures and CompoundsExample

• A mixture of iron fillings and sulphur looks different from the individual elements.

• This mixture has the properties of both iron and sulfur.• A magnet can be used to separate the iron fillings from the sulfur

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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.

• 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.


heatt

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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

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

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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%)

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Seperating Solid Mixtures

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?

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Distillation

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

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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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CrystallisationCrystallisation 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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EvaporationEvaporation 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 CentrifugationThe 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.

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Seperating Liquid Mixtures

Liquids are divided into two:Miscible LiquidsImmiscible LiquidsDefinition 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.

http://www.mentorials.com/high-school-chemistry-matter-separation-of-mixtures.htm

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FiltrationFiltration 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.

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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:

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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.

ConclusionAn 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.

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Date post:	17-Aug-2015
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Elements, compound and mixture

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