CHEMISTRY SS 1 E LEARNING NOTES FIRST TERM PART 2 ...

CHEMISTRY SS 1

E – LEARNING NOTES

FIRST TERM PART 2

PARTICULATE NATURE OF MATTER

OBJECTIVES

At the end of this topic, you should be able to:

1. Define Atom, molecule and ions.

2. Distinguish between atoms and molecules.

3. Describe how the particles are in e arranged in the atom.

4. Define:

- Atomic number

- Mass number

5. Calculate the relative atomic masses of atoms.

THE CONCEPT OF ATOMS, MOLECULES, AND IONS

Matter is defined as any substance that has mass and occupies space. It is made up of discrete (tiny)

particles known as the building blocks of matter and they are:

Atom

Molecules and

Ions.

ATOM: An atom is the smallest particle of an element which can take part in a chemical reaction.

Atoms are the smallest possible particles of an element that could exist and still possess the chemical

properties of that element. Atoms of different elements have various shapes.

MOLECULE: A molecule is the smallest particle of a substance that is capable of independent

existence, and still retains the chemical properties of that substance. A molecule is formed when two or

more atoms are chemically joined together. The combination of atoms of the same type produces

molecule of an element, e.g. H2, O2, N2, and Cl2, while the combination of different types of atoms

produces molecule of a compound e.g. sodium chloride, NaCl, calcium chloride, CaCl2, hydrogen

chloride, HCl etc. Thus, molecules are the smallest amounts in which any substance can exist without

losing its identity.

NOTE: The number of atoms in a molecule of an element is called its ATOMICITY.

Most gaseous elements like hydrogen (H2), oxygen (O2), nitrogen (N2) and chlorine (Cl2) are diatomic,

i.e., the molecule consists of two atoms.

Others like phosphorus (P4), and sulphur (S8), exist as tetratomic and polyatomic molecules

respectively. The molecules of Helium (He), Neon (Ne), Argon (Ar), and others are monoatomic,

because they can exist independently as single atoms.

ELEMENTS, FORMULA OF MOLECULE, ATOMICITY AND NAME

Element Formula of

molecule

Name Atomicity

CHEMISTRY @ OLASS, YABA.

SS 1 CHEMISTRY BY OTEGA OMOYIBO (TEGAMATICS) 1

Helium

Neon

Argon

Hydrogen

Oxygen

Nitrogen

Chlorine

Ozone

Phosphorus

Sulphur

Не

Ne

Ar

H2

O2

N2

Cl2

O3

P4

S8

1

1

1

2

2

2

2

3

4

8

Monoatomic

Monoatomic

Monoatomic

diatomic

diatomic

diatomic

diatomic

triatomic

tetratomic

polyatomic

NOTE: The distinction between atom and molecule of an element is that, atom is the smallest particle

which can participate in chemical reactions, while molecule is the smallest particle which can normally

exist when the element is not involved in chemical reaction.

IONS: Ions are any atom or a group of atoms which possesses an electric charge. There are two types

of ions:

(i) The positively charged ions or cations, e.g. K+, Na+, Ca2+, Fe2+ NH4+, etc.

(ii) The negatively charged ions or anions, e.g. OH-, CI-, NO3-, SO4

2- etc.

NOTE: Ions are produced when atoms lose or gain electrons e.g.

Na – e- Na+

Mg – 2e- Mg2+

Cl + e- CI-

S+ 2e- S2-

HISTORY OF THE ATOM

The word 'atom' comes from a Greek word which means something that cannot be split. This fits in

nicely with Dalton's ideas about atoms. However, atoms can be split.

In the late 1800s and early 1900s scientists had to think up new pictures of atoms to explain new

observations. For example, in 1897 J.J. Thomson put forward his "plum pudding' theory. He thought

atoms were balls of negative charge with tiny positive particles struck inside. The negative particles

were called electrons. He said they were like the currants in a bun or Christmas pudding

This model explained Thomson's experiment with electricity i.e. cathode rays experiment. However,

later experiments using radioactive particles needed a new picture. By 1915, scientists, like Ernest

Rutherford and Niels Bohr, had developed a model that is still useful today.



400 BC - Democritus suggested that all things are made of particles and scientists still believe this.

1805 - John Dalton's atomic theory. Atoms of the same element are all alike. They combine to make

compounds.

1897 - J.J. Thomson found the electron, a negatively charged particle that flies round the nucleus.

1886 - Eugene Goldstein discovered the proton, a positively charged particle. This was later reiterated

by Ernest Rutherford in 1909 as positively charged particles that cuddle with neutrons to form the

nucleus of the atom.

1911 - Ernest Rutherford discovered the nucleus of the atom. The centre of the atom which is incredibly

small and dense.

1913 – Niels Bohr suggested that electrons are found in shells around the nucleus.

1932 – James Chadwick discovered the existence of neutrons. A particle of equal mass with proton but

carries no charge.

DALTON'S ATOMIC THEORY

The idea that elements are made up of atoms is called the atomic theory. Credit for the first atomic

theory is usually given to the ancient Greek philosophers. However, this concept may have had its

origins in the events of earlier civilisation. In 1808, John Dalton of England put forward his famous

atom's theory which states as follows:

1. All elements are made up of small indivisible particles called atoms.

2. Atoms cannot be created or destroyed.

3. Atoms of the same elements are exactly alike in every aspect and are different from atoms of all other

elements.

4. Atoms of different elements can combine in simple whole numbers of ratios to form compounds.

5. All chemical changes result from the combination or the separation of atoms.

Dalton's atomic theory, based on experimentation and chemical laws known at that time, assigned

weights and combining capacities to the postulated atoms. The theory in its broad outline is still valid,

however, some of the particulars have been modified in the light of modern discovery, but the principal

aspects as outlined are still useful in the study of chemistry. The

MODIFICATION OF DALTON'S ATOMIC THEORY

1. All elements are made up of small indivisible particles called atoms: The atomic nature of

elements is not disputed. Atoms can, however, no longer be regarded as indivisible because according

to Rutherford's discovery, atom is made up of three main subatomic particles called protons, neutrons,

and electrons.

2. Atoms cannot be created or destroyed: This statement is still acceptable for ordinary chemical

reactions. The changes associated with nuclear fission, destroy atoms of the element involved, in the

sense that the nuclei are broken into smaller units which correspond to simpler atoms, e.g., the nucleus



of uranium – 235, can absorb a neutron and then break up into two unequal fragments which form

simpler atoms, while a large amount of heat energy is released.

3. Atoms of the same elements are alike in every aspect and differ from atoms of all other

elements: The discovery of isotopes contradicts this statement.

4. Atoms of different elements combine in simple whole number ratios to form compound: This

statement is still acceptable for inorganic compounds which usually contain few atoms per molecule.

Carbon, however, forms very large organic compounds such as proteins, fats and starch which contain

thousands of atoms. Silicon, which is inorganic, also forms some very complex trioxosilicates (IV)

involving large number of atoms.

THE MODERN ATOMIC THEORY

The modified Dalton's atomic theory is referred to as the modern atomic theory and - consists of the

following features:

1. All matter is composed of small particles, some of which are electrically neutral, some are positively

charged while some are negatively charged.

2. Atoms of the same element are not alike but may have different masses.

3. An element may have atoms with different masses. These atoms of the same element with different

masses are called Isotopes.

4. Atoms of different elements can combine together to form molecules.

5. Molecules are the smallest particles of compounds that have the properties of the compound.

6. Molecules may be further broken down and when this happens, they no longer have the characteristics

of the compound.

7. The molecules of a compound consist of the atoms of the elements that form the molecules.

8. The molecules of a compound have definite compositions and structures.

CONSTITUENTS/STRUCTURE OF THE ATOM

Atoms are themselves built up from many smaller particles, three of which are of direct interest to the

chemist. The three particles which are also regarded as “fundamental particles” are the proton, the

electron and the neutron.

The proton is a positively charged particle of mass equal to that of a hydrogen atom (using

carbon-12 as standard).

The electron is negatively charged, its charge being equal in magnitude but of opposite sign to

the charge on a proton. It has a very small mass of about 1

1840 of the mass of the proton.

The neutron has no charge (electrically neutral) and its mass is equal to the mass of a proton.



According to Rutherford's nuclear theory (1906), the neutron and proton make up the nucleus of the

atom. The nucleus is positively charged and surrounded by the electrons in an orbital manner. Atoms

are electrically neutral because they contain the same number of electrons and protons.

Properties Of Fundamental Subatomic Particles

Particle Mass Charge

Proton

Neutron

Electron

1 unit

1 unit

1/1840 unit

Positive (+)

Neutral

Negative(-)

THE ARRANGEMENT OF ELECTRONS AROUND THE NUCLEUS

The arrangement of electrons around the nucleus is known as electronic configuration. Niel Bohr in

1913 suggested that the electrons in an atom revolve round the centrally placed nucleus along certain

imaginary circular paths called Orbitals or Shells, situated at various distances from the nucleus. These

shells are denoted by letters K, L, M, N, O, P, Q and are associated with definite energy content of the

electron, increasing outwards from the nucleus shell k which is nearest to the nucleus and has the lowest

energy. It contains the least number of electrons which is two and cannot hold more than two.

The maximum possible number of electrons in a shell numbered “n” is 2n2 where n is the shell number.

Therefore:

K shell = 2n2 = 2(1)2 = 2. So K shell has maximum 2 electrons

L shell = 2n2 = 2(2)2 = 8. So L shell has maximum of 8 electrons

M shell = 2n2 = 2(3)2 = 8. So M shell has maximum of 18 electrons

ELECTRON SHELLS

The electrons in the atom are arranged in shells around the nucleus. The shells are sometimes called

energy-levels.

The first shell (nearest to the nucleus) can hold just 2 electrons. The second shell can hold up to 8

electrons.



The third shell can also hold up to 18 electrons.

ELECTRONIC CONFIGURATIONS OF SOME ELEMENTS

So we can write/represent the electronic configuration of elements based on K,L,M,N as follows:

Hydrogen = 1

Helium = 2

Lithium = 2,1

Beryllium = 2,2

Boron = 2,3 etc

ASSIGMENTS: write the electronic configuration of the first 20 elements starting with carbon

ATOMIC NUMBER AND MASS NUMBER

THE ATOMIC NUMBER

The atomic number of an element is the number of protons present in the atomic nucleus of the element.

It is denoted by letter Z and increased by one when the elements were arranged in order of ascending

relative atomic mass. In a neutral atom, the number of protons is equal to the number of electrons. Thus,

the atomic number is also the number of electrons. The atomic number of an element is a whole number,

where the relative atomic mass of an element is not a whole number.

Atoms with the same atomic number may have different masses and still have their properties identical.

However, no change in atomic number is possible without a major change in properties.

Atomic number of an element determines the nature of the atom and also distinguishes it from atoms

of all other elements.

THE MASS NUMBER

The mass number of an element is the sum of the protons and the neutrons in the atomic nucleus of the

element, e.g. fluorine has a mass number of 19. The number of proton is 9 while neutron is 10.

We can describe an atom of an element by writing its symbol together with its atomic number and mass

number, e.g. 𝑋 𝑍𝐴 where A represent mass number and Z represent atomic number and X can be any

element, e.g. calcium is 𝐶𝑎2040 , fluorine is 𝐹9

19 etc.



RELATIVE ATOMIC MASS

The relative atomic mass of an element is the number of times the average mass of one atom of the

element is heavier than one-twelfth of the mass of one atom of carbon – 12. i.e, it is the average mass

of the atoms of the element on a scale on which one atom of the carbon - 12 isotope is 12 units.

NOTE: The relative atomic mass carries no units

RELATIVE MOLECULAR MASS

The relative molecular mass of a compound is the sum of the relative atomic masses of all the atoms in

one molecule of the substance. It is the mass of the correctly written formula or molecule of a compound

obtained by adding together the appropriate relative atomic masses of all the atoms of the elements

present.

NOTE: Relative molecular mass is also referred to as the formula mass.

Example 1

Calculate the relative molecular mass of sodium tetraoxosulphate (VI), Na2SO4, (Na = 23, S= 32, O=

16)

Solution

1 molecule at Na2SO4 contain 2 sodium,1 sulphur and 4 oxygen atoms

:. Relative molecular mass of Na2SO4

2Na + S + 4(O)

= (2 x 23) + (1 x 32) + (4 x 16)

= 46+ 32 + 64

= 142

Example 2

Calculate the relative molecular mass of calcium chloride, CaCl2 (Ca = 40, C1= 35.5)

Solution

1 molecule of CaCl2, 1 calcium, and 2 chlorine atoms.

:. Relative molecular mass of CaCl2

Ca + 2Cl

= (1 x 40) + (2 x 35.5)

= 40 + 71= 110



Example 3

What is the formula mass of aluminium tetraoxosulphate (VI). (RAMs, Al = 27, S= 32,O = 16)

Solution

1 mole of Al2(SO4)3 contains: 2 Al, 3S, and 12O

Therefore the relative formula mass of Aluminium tetraoxosulphate (VI) is 342.

ASSIGNMENT: Calculate the RMM of the following compound:

(NH4)2CO3

CuCO3

Ca(NO3)2

Na2CO3.10H2O

FeCl3

(H = 1, C = 12, N = 14, O = 16, Na = 23, Cl = 35.5, Fe = 56, Cu = 64,

CALCULATIONS INVOLVING MASS NUMBER AND SUB-ATOMIC PARTICLES

Important fact:

In an atom:

Atomic number = proton number = electron number

Mass number = proton number + neutron number

In an ion:

Atomic number = proton number

Electron number = proton number ± number of charge

Example 1: Calculate the number of neutron in the following

i. 𝑁𝑎1123 ii. 𝐶𝑎20

40 iii. 𝐶𝑢2963.5

Example 2: An element X has a proton number of 19 and neutron number of 20. Find the mass number

Example 3: Find the neutron number in the following:

i. 19𝑌2+ ii. 13𝑊3+ iii. 8𝑋2−

ISOTOPES

Isotopes are atoms with the same atomic number but different mass number. This is due to differences

in the number of neutrons.

Isotopy is a phenomena whereby an atom exist in different forms having the same atomic number but

different mass number

Isotopes of an element have different physical properties, but exhibit the same chemical properties,

because neutrons appear to have no influence on the chemical properties of the atom but their major

effect is in contributing to the mass of the atom.



An atom showing these characteristic properties is said to show isotopy and the varieties of the atoms

are called Isotopes of the element. A well-known example of isotopy occurs in chlorine.

Analysis of the chlorine Isotopes

Isotope 𝐶𝑙1735 Isotope 𝐶𝑙17

37

Mass number

Atomic number

Number of protons

Number of electrons

Number of Neutrons

Abundance in nature (%)

35

17

17

17

35 – 17 = 18

75

37

17

17

17

37 -17 =20

25

Other examples of element exhibiting isotopy include:

Oxygen: 𝑂816 , 𝑂8

17 , 𝑂818

Carbon: 𝐶612 , 𝐶6

13

Sodium: 𝑁𝑎1123 , 𝑁𝑎11

24 etc.

CALCULATIONS INVOLVING ISOTOPES

To solve problems on isotopes, the formula is used:

RAM = Abundance A + abundance B + ….

Where RAM means relative atomic mass of the element

Abundance A = %𝑜𝑐𝑐𝑢𝑟𝑒𝑛𝑐𝑒 𝑜𝑓 𝑖𝑠𝑜𝑡𝑜𝑝𝑒 𝐴

100× 𝑚𝑎𝑠𝑠 𝑛𝑜 𝑜𝑓 𝐴 or

𝑟𝑎𝑡𝑖𝑜 𝑜𝑓 𝐴

𝑡𝑜𝑡𝑎𝑙 𝑟𝑎𝑡𝑖𝑜× 𝑚𝑎𝑠𝑠 𝑛𝑜 𝑜𝑓 𝐴

Abundance B = %𝑜𝑐𝑐𝑢𝑟𝑒𝑛𝑐𝑒 𝑜𝑓 𝑖𝑠𝑜𝑡𝑜𝑝𝑒 𝐵

100× 𝑚𝑎𝑠𝑠 𝑛𝑜 𝑜𝑓 𝐵 or

𝑟𝑎𝑡𝑖𝑜 𝑜𝑓 𝐵

𝑡𝑜𝑡𝑎𝑙 𝑟𝑎𝑡𝑖𝑜× 𝑚𝑎𝑠𝑠 𝑛𝑜 𝑜𝑓 𝐵

Examples:

1. An element X has two isotopes of 𝑋1020 and 𝑋10

22 in the ratio 1 : 3. What is the relative atomic

mass of X

2. Calculate the relative atomic mass of chlorine whose isotopic mixture are 𝐶𝑙1735 and 𝐶𝑙17

37 at 75%

and 25%.

i. Determine the neutron of each isotopes

3. The relative atomic mass of an element is 21.5. The two isotopes of the elements are 𝑋1020 and

𝑋10𝑥 occurring at 25% and 75% respectively in nature. Calculate x.

4. Calculate the abundance of each chlorine isotopes whose isotopic mixture are 𝐶𝑙1735 and 𝐶𝑙17

37



SEPARATION TECHNIQUES

OBJECTIVES

At the end of this topic, you should be able to:

1. State the different standard methods of separating mixtures and their individual

applications.

2. Manipulate different apparatus for separation.

3. Draw separation technique apparatus.

4. State the criteria for purity.

5. Distinguish between pure and impure substances.

One of the distinctive properties of a mixture of substances is that it is possible to separate the

constituents by physical means. Each constituent of a mixture still retains its individual properties. We

can take advantage of this characteristic to separate mixtures.

There are many different physical methods used to separate a wide variety of mixtures.

The particular method employed for any given mixture depends upon the properties of its constituents,

such as differences in solubilities, boiling points, sublimation, rates of diffusion, rates of movement

over an absorbent medium or magnetic property.

Types of Separation Techniques

Sieving

Decantation

Filtration

Evaporation

Distillation

Fractional distillation

Crystallisation

Fractional crystallisation

Sublimation

Centrifugation

Precipitation

Magnetic separation

Chromatography

1. Sieving

Sieving is the method separating solid particles of different sizes. The solid particle is placed on a sieve

with a mesh of a particular size. Particles smaller than the mesh size of the sieve will pass through the

sieve, while the bigger particles remain on the sieve. This method is used extensively in

Mining and

Garri production in West Africa

2. Decantation

Decantation is a method used to separate a mixture of liquid and denser solid particles which separate

into two distinct layers on standing. The upper layer of clear liquid is carefully poured from the bottom

solid portion into another container.



NOTE: Decantation is a quick but inaccurate method of separation, because during the process, the

solid which settles at the bottom becomes agitated and some of it may mix up again with the liquid

portion.

3. Filtration

Filtration is the method of separating insoluble particles from liquids through the pores of the filter

paper. During filtration, the liquid portion passes through the filter paper. The liquid which passes

through the filter paper is called the filtrate while the portion which remains on the filter paper is called

the residue.

An example of mixture separated by filtration is suspension of chalk dust in water. When it is poured

onto a filter paper, the water passes through, leaving the chalk particles on the filter paper.

NOTE: Filtration gives better result than decantation.

Industries that uses filtration method of separation include:

Water purification plants and

Breweries

4. Evaporation

This is a method of separating a dissolved solute from a solution by heating the mixture to dryness so

that the liquid portion with a lower vapour pressure than the solid is removed from the solid portion,

e.g. salt solution.

The method employs the principle of different vapour pressures and the solvent is sacrificed in the

process. The salt solution is poured into an evaporating dish and heated gently over a water bath or

sand bath on the bunsen flame. The water is driven off and the salt is left behind in the dish.



NOTE: Evaporation may be difficult to control; as a solution may spatter and the: solid may

decompose.

Evaporation is used in Salt-making industries.

5. Distillation Distillation is used to recover a solvent from a solution. In other words, it is a process of vapourising a

liquid and then condensing the vapour. The solution is heated in a flask to vapourise the solvent. The

vapour passes along a condenser which is cooled by circulating water in its outer jacket. The process of

cooling a vapour to a liquid is called condensation. NOTE: A mixture of two liquids with widely

different boilling points can be separated by evaporating one from the other and recondensing it in a

separate container, e.g. a mixture of ethanol (78°c) and water (100°c).

Ethanol boils at about 78°c and the vapour is given off at this temperature and passes into the inner tube

of the condenser where it is cooled by the circulating cold water. The vapour condenses and ethanol can

be collected in the beaker

Distillation can be used to purify liquids and

in Gin distilleries.

6. Fractional distillation

Fractional distillation is used to separate a mixture of two or more mixed liquids with close boiling

points into its component fractions. A fractional distillation apparatus is the same as in simple

distillation, except that a fractionating column is introduced in - between the distillation flask and the

condenser. The fractionating column is packed with glass beads, and this is where the actual separation

is carried out. The upper part of the column is at a lower temperature than the lower portion. Thus,



vapours with higher boiling points would condense as they enter the upper portion of the fractionating

column and flow back into the distillation flask. Fractional distillation process is repeated until all the

component fractions in the mixture are distilled over.

Petroleum contains many important fractions such as natural gases, petrol, kerosene,

gas oil, heavy oil and bitumen. Each of these fractions can be recovered in its pure form

by fractional distillation.

Fractional distillation can also be used to separate a mixture of benzene methyl benzene

and liquefied air into pure nitrogen, oxygen, and noble gases.

7. Crystallisation:

Crystallisation is used to separate salts which decompose easily on heating from their solutions. It is the

phenomenon by which crystals are formed from liquid, super saturated solution based on the differences

in melting point of the substances. The salt crystals obtained are pure and they contain water of

crystalization, e.g. copper (II) tetraoxosulphate (VI) pentahydrate CuSO4.5H2O, copper (II) trioxonitrate

(v) trihydrate, Cu(NO3)2.3H,O, Iron (II) trioxosulphate(VI)heptahydrate, FeSO3.7H,O etc.

The use of crystalization as a purification process takes place where the impurity in the substance is

insoluble in the solvent. The impure solid is dissolved in a suitable solvent, leaving the impurities as an

insoluble residue. The solution is filtered and heated to drive away some of the solvent until the solution

becomes saturated. When the saturated solution is cooled, crystals of the solute begin to form.

Crystallization is used in the manufacture of drugs and

Sugar where purity of the product is important.

8. Fractional crystallization

Fractional crystallisation is used to separate two or more solid solute which are present in roughly equal

amount in the same solution. The solubility of the different solute in the given solvent must differ

at different temperature. During the cooling process, at a particular temperature, crystals of relevant

solute will come out of solution, leaving behind the others which are still in their limit of solubility

9. Sublimation: Sublimation is use to separate solid substance which sublime from other solids. The vapours of certain

substances, where cooled, condense directly to become solid. These solids, when heated, also change



directly to the gaseous state without going through the liquid state. This physical change is called

sublimation.

NOTE: Iodine, benzoic acid, sulphur, iron (III) chloride and ammonium chloride are common examples

of substances that sublime. These substances can be separated from other solids by sublimation, e.g. a

mixture of iodine and sodium chloride, on heating the iodine sublimes and re-form as solid at the cooler

part of the apparatus. The reformed solid is known as the sublimate.

Industries that produces substances that sublime e.g iodine, petroleum etc, make

use of sublimation method

10. Precipitation: As a chemical process, precipitation uses the property of differences in solubilities of solids in different

mixable liquids to precipitate the solid. It is carried out by adding a solvent to an aqueous solution of a

substance. For example, iron (III) is soluble in water and insoluble in ethanol. Adding ethanol to an

aqueous solution of iron (II) tetraoxosulphate which can be separated by filtration and be recrystalised,

if necessary to get a high degree of purity. Another way of demonstrating precipitation is by mixing

two different solutions which react to produce one soluble compound and an insoluble substance called

the precipitate, e.g. when a solution of sodium chloride, is added to a solution of silver trioxonitrate (v),

a soluble sodium trioxonitrate (v) and an insoluble silver chloride are formed. NaCl(aq) + AgNO3(aq)

→ AgCl + NaNO3(aq)

This method is mostly employed in the laboratory for analytical work

11. Chromatography: Chromatography is a method of separating the constituents of a mixture by

taking advantage of their different rates of movement in a solvent over an absorbent

medium. Chromatography is a means of separation and analysis that utilizes fractional

separation. It is based on the principle that if a fluid containing a number of substances is

allowed to pass through an absorbent medium, the different substances in the fluid may travel

at different rates and be separated.

The rate of movement depends on the relative affinities of the constituents for the solvent and the

adsorbent medium. i.e., solutes which are weakly adsorbed by the adsorbent medium are easily re-

dissolved by the ascending solvent and travel quickly up the adsorbent medium. In addition, solutes

which are very soluble in the solvent move up at a faster rate than those which are not so soluble.

Two advantages of chromatography are:

It can be performed with very small masses of the material.

The substances are not destroyed in the process.



TYPES OF CHROMATOGRAPHY

1. Paper chromatography

2. Column chromatography

3. Thin layer chromatography

4. Gas chromatography

5. Ion-exchange chromatography etc.

The commonest and the least complicated method is the paper chromatography which uses filter paper

as the adsorbent medium, and a variety of solvent such as ethanol, methanol, chloroform, ethyl

ethanoate or aqueous phenol can be used.

A spot of solution containing the mixture to be separated is placed near one end of the filter paper with

a faint pencil line across the breath of the filter paper through the spotted mixture. The paper is then

suspended vertically in a closed air-tight jar with the spotted end immersed in the solvent but the spot

well clear of the solvent level. As the solvent moves up the paper, the different solutes in the mixtures

move along the paper strip together with the solvent at different speed and become separated. The paper

strip is removed from the jar when the ascending front of the solvent is approaching the top of the paper.

The paper strip is dried and sprayed, if necessary, with appropriate chemical reagents to locate the

positions of the various spots of solute along the paper strip. Each solute is identified by the distance it

has travelled and this is achieved by comparing its distance with those of known standard substances.

The separation as it appears on the filter paper strip is known as chromatogram.

Chromatography can be used to separate the dyes and coloured ink

It is used in medicine to analyse blood or urine.

Industrially, it can also be used to identify the components of petroleum.

12. Separating funnel method

Separating funnel can be used to separate two or more liquids which cannot mix together to form a

single liquid. The liquids have different densities. A mixture of petrol and water is an example of a

mixture that can be separated by this method. The liquid separate out into two distinct layers with the

less dense liquid (petrol) floating on top, leaving the more dense liquid (water) at the bottom. When the

tap is opened, the lower denser liquid layer is tapped off leaving the upper less dense liquid layer in the

separating funnel which can be run off into another container.



13. Magnetic Separation:

Magnetic substance are separated from non-magnetic particles in a mixture by a magnet. A mixture of

iron fillings and sulphur powder can be separated by this method. A bar magnet is used to stir the

mixture and the iron fillings stick to the magnet, leaving the sulphur behind.

This method is used in steel industry and also to remove magnetic impurities from tin

ore.

PURE AND IMPURE SUBSTANCES

The separation techniques described above are used for the preparation of chemical substances in a pure

state. An impure substance can be regarded as a mixture of pure substance and impurity. Impurities

lower the melting point of a substance and raised its boiling point.

PURE SUBSTANCES (TEST FOR PURITY)

(i) Melting Point and Boiling Point:

The melting point and the boiling point of a given pure substance is fix at particular

temperature and can be determined. This temperature is affected if impurities are present,

e.g. ice melts at 0°c (373K) while pure water and pure ethanol boil at 100°c (373K) and

78°c (351K) respectively.

(ii) Density: The density of a substance is a physical property. Every pure substance has its

definite density. The density of an impure substance is different from that of the pure

substance. The difference in the value of the densities of pure and an impure substance

depends on the nature and quantity of impurity in the substance.

(iii) In the case of coloured substances, a pure substance gives a spot on a paper chromatogram.

CHEMISTRY SS 1 E LEARNING NOTES FIRST TERM PART 2 ...

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