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Chemistry A Level
Module 2: Foundations in chemistry
Basic atomic structure - 

The nucleus is made up of protons and neutrons
...
It accounts for most of the atoms mass
...

Subatomic particles Relative Mass
Proton
1
Neutron
1
Electron
1/2000

Relative charge
+1
0
-1

Nuclear symbols Mass number = A (protons + neutrons in the nucleus)
Atomic number = Z (protons/electrons)
Element symbol = X
Evidence for the structure of atoms • JJ Thomson (1897-1906)

Cathode ray tubes emitted cathode rays, which were negatively charged particles with a
very small mass that could be deflected by a magnet or electronic field
...
This disproved Dalton, who said atoms couldn’t be split further
...
Most particles passed through as
expected, but some were deflected back, suggesting atoms had a concentrated positive
charge in the nucleus of the atom
...

• N Bohr (1913)

Adjusted Rutherford’s model by sating electrons must be within shells that followed
certain paths, otherwise they would spiral into the nucleus
...
The amount of energy released
when an electron changes quantum number is the quanta
...
It was later discovered to be the neutron
Isotopes - 

Isotopes are atoms of the same element with different numbers of neutrons and therefore
different masses
...
Because of this
they have similar chemical and reactive properties, but different physical properties
...
Cations are positive ions, anions are negative ions
...
1u has a mass of 1
...
The mass of a carbon-12 atom is 12u, therefore the mass of 1/12th of a
carbon-12 atom is 1u
...

Relative atomic mass (Ar) The weighted mean mass of an atom of an element compared with 1/12th the mass of an
atom of carbon-12
...
e
...
The mass of a molecule is compared to the mass of an atom of carbon-12
...
g
...
The y-axis of a mass spectra
shows relative/percentage abundance and the x-axis shows m/z (mass/charge of ion)
ratio
...

Relative atomic mass can be determined from the spectra by calculating the sum of the
relative isotopic masses by its abundance and dividing this sum by the sum of the
abundances
...

Elements in the same group react similarly
...

Atoms of non-metals (groups 15-17) form negative ions by gaining electrons to form the
same electron configuration as the next noble gas in the periodic table
...

Oxidation numbers (written as Roman Numerals) show which ion has been formed when
an element can form more than one ion
...
g
...

Key ions include;
- NO3• Nitrate

•
•
•
•
•
•

Carbonate - CO32Sulfate
- SO42Hydroxide - OHAmmonium - NH4+
Zinc
- Zn2+
Silver
- Ag+

Ionic compounds Positive and negative ions ionically bond to
form a compound with no overall charge
...
A binary
compound contains two elements only; it is
named using the name of the first element
followed by the name of the second
element but with the suffix -ide
...


Polyatomic ions are ionic compounds containing more than one element bonded together
...

1
...
This gives the molar ratio
...
Divide each molar ratio by the smallest number to give a 1:x ratio

[NB: Percentages can be used to find molar ratio]
3
...

Empirical formula is particularly useful for giant structures
...

The molecular formula can be calculated by dividing the molecular mass by the mass of
the empirical formula
...
This shows reaction stoichiometry
...

Types of species • Atom
• Ion
• Molecule
• Empirical formula to represent giant structures (i
...
ionic compounds, macromolecules,
metals, carbon, silicon and boron)
• Electron
State symbols • (s) - solid
• (l) - liquid
• (g) - gas
• (aq) - aqueous

Ionic equations Ionic equations show ionic reactions in water
...

Amount of substance and the mole Given the symbol n, amount of substance is a measure of number of particles, based on
the Avogadro constant (NA)
...
022 x 10-23
mol-1
...
A mole of a substance
contains NA particles
...
]
Molar mass is the mass per mole of a substance
...


[NB: Mr = M]
Number of moles = mass of substance
molar mass
Moles and gas volumes At RTP a mole of any gas occupies 24 dm3mol-1 of space
...

Molar gas volume is the volume per mole of gas and varies with temperature and
pressure
...

Ideal gas equation Gases are assumed to behave in an ideal way
...

pV = nRT
where;
p = pressure (Pa)
V = volume (m3)
n = number of moles
R = gas constant (8
...
Its
units are moldm-3, which can also be denoted as M
...

Concentrated solutions have large amounts of solute per dm3, whereas dilute solutions
have a small amount
...

A standard solution is a solution of known concentration
...
The dissolved solution is transferred
to a volumetric flask and solvent is added to the flask
...

The flask is then inverted several times to mix the substances thoroughly
...

A reaction may not obtain 100% yield because;
• the reaction may be at equilibrium and not completion
• side reactions may occur
• reactants may not be pure
• reactants/products may be left in the apparatus
• separation and purification may lead to losses
The limiting reagent is the reagent that is not in excess, so will be used up first
...

Atom economy Atom economy is calculated by dividing the Mr of the desired products by the sum of all the
products Mr and multiplying by 100
...

Less waste has to be disposed of
...

Acids Acids are proton donors
...
They have a pH
less than 7
...

HA + H2O —> H3O+ + AA strong acid almost fully dissociates - the forward reaction is more prevalent
...

A weak acid ionises only slightly in water, so it only partially dissociates and releases few
H+ ions so that HA ⇌ H+ + A-
...
The
cation (positive ion) is a metal ion or ammonium ion
...

An acid salt can be formed when the acid is diuretic and only one H+ ion is released
...
g
...

Salts can be formed by neutralising acids and bases:
• acid + base —> salt + water
• acid + metal carbonate —> salt + carbon dioxide + water
• acid + metal oxide —> salt + water
• acid + metal —> salt + hydrogen

Bases Bases are proton acceptors
...
0
...

Common bases • Metal oxides
• Metal hydroxides
• Ammonia
• Amines
Common alkalis - strong base
• Sodium hydroxide (NaOH)
Potassium hydroxide (KOH) - strong base
•
- weak base
• Ammonia (NH3)
Amphoteric substances Amphoteric substances are substances that can behave as both acids and bases, for
example the amino acid glycine
...
For example,
ammonium and nitric acid form ammonium nitrates, which dissociates in NH4+ and NO3- in
water
...
Water of crystallisation refers to water
molecules that form part of the crystalline lattice structure of a salt
...
g
...
H2O)
...
The ratio of moles of anhydrous salt to water molecules lost
is then found
...


When calculating the ratio of water of crystallisation to salt, the following assumptions are
made;
- All the water has been lost once the mass of the salt remains constant following
continual heating
- No further decomposition of the salt has taken place under heat
Titrations Titrations refer to using a known concentration of one solution to find the concentration,
purity, molar mass or formula of another solution
...
Use a pipette to add a measured volume of solution (unknown concentration) to a
conical flask
...
05cm3
2
...
Add the solution in the burette until the reaction has just completed and the end point
is reached
...
Carry out an accurate titration - where solution is added 2cm3 before the end point then
added drop by drop
5
...
10cm3) results are achieved and
calculate the moles of each reactant used [NB: when calculating the number of moles
to neutralise an acid, the number must be doubled if the acid is diprotic]
Indicators Oxidation numbers Oxidation numbers tell you the number of electrons an element has donated/accepted to
form an ions or part of a compound
...


[NB: they are written as charge then number]
Oxidation rules 1
...
Combined oxygen has an oxidation number of -2
3
...
Combined hydrogen has an oxidation number of +1
5
...
Simple ions have the same oxidation number as their charge
7
...
Oxygen has an oxidation number of +2 when combined with fluorine
9
...
Molecular ions have the same oxidation number as their charge
Oxyanions Oxyanions are negative ions containing oxygen
...

e
...
NO2- —> Nitrate (III) —> N: +3
NO3- —> Nitrate (V) —> N: +5
Redox reactions Redox reactions occur when both a reduction and oxidation reaction happen
simultaneously
...
Reduction leads to a decrease in oxidation number, whereas
oxidation leads to an increase in oxidation number
...
In the reaction of metals and dilute acids, the metal is
oxidised and the hydrogen is reduced
...
A shell is a group of atomic orbitals with
the same principal quantum number, n
...
When electrons move energy levels they emit or absorb radiation
...

An orbital is a region of space where electrons may be found
...
Orbitals within the same sub-shell have the same energy
...


Sub-shell

No
...
Electron energy level diagrams show the
different energy levels of sub-shells within a shell
...
g
...
Electrons fill lower energy sub-shells first [NB: 3d
has a higher energy level than 4s]
2
...
Paired electrons have opposite spins; the arrows are written so that they face opposite
directions
Ionic bonding Ionic bonding describes strong electrostatic attraction between oppositely charged ions
...


Giant ionic lattices These are ionic compounds in the solid state and exist as repeating ionic units
...

Properties include;
• High melting and boiling points due to strong electrostatic forces between ions in all
directions
...
g
...
As ionic charge increase, solubility decreases
because the attractions between the ions are greater than those between the ions and
water molecules
...
The
shared pair of electrons are attracted to both the positive
nuclei, causing an overlap of orbitals
...

Exceptions to this case include BF3 and several group 15, 16
and 17 elements, which can expand their octet (e
...
SF6)
...

They are illustrated using dot-and-cross diagrams
...
Atoms may also have lone pairs
of electrons
...

A dative covalent bond is formed when one of the bonding atoms
supplies both the electrons to the covalent bond, such as in the
ammonium ion and oxonium ion
...
Because of these easily overcome intermolecular forces
there have relatively low melting and boiling points
...
Polar covalent molecules can

dissolve in polar solvents
...

Giant covalent structures Giant covalent structures are lattices of atoms all covalently bonded
...
These strong bonds are unable to be overcome by
both polar and non-polar solvents, so the compounds are insoluble
...
These can carry currents of electricity
...
Two lone pairs repel the most (109
...
5 degrees
less and bonded to bonded pairs repel the least (again
2
...
5 degrees)
...
5 degrees
and ammonia has a pyramidal shape with an angle of
107 degrees
...

1

Bonded
electron pairs

2

3

4

5

6

Name of
shape

linear

linear

trigonal
planar

tetrahedral

trigonal
bypyramidal

octahedral

Example
molecule

H2

CO2

BF3

CH4

PCl5

SF6

Diagram

Shape and
bond angles

Electronegativity Electronegativity is the ability of an atom to attract the bonding electrons in a covalent
bond
...
Bonds with atoms with different Pauling electronegativity values
are said to be polar covalent bonds and have permanent dipoles (if the difference is
greater than 1
...
A molecule is polar if the
directions of polar bonds don’t cancel each other out (i
...
the element isn’t symmetrical)
...


Intermolecular forces Intermolecular forces are the forces holding molecules together and occur due to random
movements of the electrons within the shells of the atoms in molecules
...

There are four main types; permanent dipole - induced dipole interactions, permanent
dipole - permanent dipole interactions, London (dispersion) forces and hydrogen bonding
...
The molecules become slightly attracted to each
other
...

London (dispersion) forces
The constant random movement of electrons in non-polar molecules causes an
instantaneous dipole, which induces a dipole in a neighbouring molecule
...
The greater the number of electrons in
a molecule, the greater the attraction between molecules, which is demonstrated by the
increasing boiling points of noble gas molecules
...

The electron-deficient hydrogen has a small positive dipole,
which attracts the lone pair of electrons on the highly
electronegative O, N or F
...

A hydrogen bond has about 5% the strength of a covalent bond
...
The
periods show repeating trends in physical
and chemical properties, known as
periodicity
...
e
...

Across a period elements change from
metals to non-metals
...

The periodic table is divided into the s-block,
d-block, p-block and f-block
...

The history of the periodic table • Antoine-Laurent de Lavoisier (1789)

Compiled a list of substances that could not be broken down any further, known as
elements
...
He
distinguished between metals and non-metals, but also include compounds, light and
heat as elements
...
g
...
He also left spaces for undiscovered elements, such as Scandium
• Henry Moseley (1913)

Henry Moseley determined the atomic number for all the elements and rearranged the
periodic table in this order
• Glenn Seaborg (1950s)

Placed the actinide series below the lanthanide series at the bottom of the periodic table
Electron shells and ionisation Ionisation occurs when atoms lose or gain electrons
...

It is affected by;
• atomic radii - a larger atomic radii means there is less

attraction between the nucleus and outermost electrons
• nuclear charge - a greater nuclear charge means there is more attraction between the
nucleus and outermost electrons
• electron shielding - greater electron shielding means there is less attraction between the
nucleus and outermost electrons
Successive ionisation energies Successive ionisation energy are a measure of the amount of energy required to remove
each electron in turn
...

Periodicity and trends in ionisation energies -

Key trends:
• Ionisation energies increase across a period because there is greater nuclear charge, a
smaller atomic radii yet the same level of electron shielding
...
The p-orbital has a higher energy
level than an s-orbital so is slightly further away from the nucleus, meaning there is less
attraction and giving the element a lower first ionisation energy
• There is a decrease between groups 15 and 16 because the outermost electron in group
16 is in a spin-paired px orbital, rather than on its own
...
The increase in nuclear charge is outweighed by
these two factors
Metallic bonding Atoms in a solid metal are held together by metallic bonding - this is where positive cations
occupy a fixed position in a lattice and held together by the electrostatic attraction caused
by delocalised electrons
...
The delocalised electrons are spread throughout the structure of the giant metallic
lattice and can therefore move
...

The properties of a giant metallic lattice include;
• High melting and boiling point due to strong electrostatic attraction between the positive
ions and delocalised electrons
• Electrical conductivity due to the delocalised electrons which can carry current
• Ductility and malleability because the electrons allow layers of ions to slide past each
other
• They tend not to be soluble, because they react with solvents

Periodicity and melting points Period 2

Li

Be

B

C

N2

O2

F2

Ne

Period 3

Na

Mg

Al

Si

P4

S8

Cl2

Ar

Structure

Giant metallic

Giant
covalent

Simple molecular

Forces

Electrostatic attraction between
positive and negative ions

Strong
forces
between
atoms

Weak intermolecular forces between
molecules

Bonding

Metallic

Covalent

Covalent with intermolecular forces

Key trends:
• Between groups 1 and 14 melting point increases gradually because there is greater
attraction in the giant structures
• Between groups 14 and 15 there is a sharp decrease in melting point because the
elements move to have simple molecular structures with weak intermolecular forces
between them
• Between groups 15 and 18 the melting points remain relatively low
Group 2 elements Group 2 elements are light metals with low densities
...
They form white compounds
...
This is why they usually lose their two
outermost electrons by a first ionisation and a subsequent second ionisation
...

Group 2 reactions • With oxygen they react vigorously in a redox reaction to form an oxide
• With water they react to form metal hydroxides
...
These hydroxides increase in solubility down the group, which increases the
alkalinity of the water
• With dilute acids they react to form a salt and hydrogen gas

Group two compounds can be used to neutralise acidic soils (calcium
hydroxide), as antacids (magnesium hydroxide) and for construction
purposes (calcium carbonate in limestone - however, limestone
reacts with acid rain so gradually erode
...
They have low
melting and boiling points and exist as diatomic molecules
...

They have 5 of their 7 outermost electrons in the p sub-shell
...
This is because their atomic radii increases and there is less attraction
between the nucleus and outermost electron shell, so they lose the ability to form -1 ions
as easily
...

Group 17 reactions • In a mix of water and cyclohexane a more reactive
halogen will oxidise and displace the halide of a
less reactive halogen
...

• Disproportionation reactions occur when the same element is both reduced and
oxidised
...


Another example is the formation of bleach using chlorine and cold dilute aqueous
sodium hydroxide; 

Cl2 + 2NaOH —> NaCl + NaClO + H2O

Chlorine is reduced in sodium chloride and oxidised in sodium hypochlorite
...
This forms a gas which can be collected and run through limewater
...
This is a white precipitate

• Halide ions X- 

An aqueous solution of the halide reacts with an
aqueous solution of silver nitrate to form a silver
halide precipitate
...


Silver bromide forms a cream precipitate which
dissolves in concentrated ammonia only
...
This turns
damp red litmus paper blue and has a distinct smell
Enthalpy Chemical energy is the
potential energy within
chemical bonds
...
It is measured in kJ
...
It is measured by
measuring the change in temperature of the surroundings, indicating the energy released
or absorbed, as the law of conservation of energy states energy cannot be created or
destroyed
...
e
...
The surroundings
are the the container within which a chemical reaction takes place
...
Average bond enthalpy is the mean energy needed to break the
bonds in one mole of gaseous bonds via homolytic fission
...

Exothermic reactions release heat, so the enthalpy change is negative as the chemical
energy of the products is less than that of the
reactants
...


Bonding breaking requires energy, whereas bond
forming releases energy
...

Endothermic reactions absorb heat, so the enthalpy
change is positive and the products have more
energy than the reactants
...
More energy is
required to break bonds than is released from the bonds formed in the products
...
Using the
change in temperature, specific heat
capacity of the surroundings and the
mass of the surroundings, the heat
exchanged can be calculated
...


Calorimetry can be measured directly by placing the
reactants in a reaction vessel
...
The temperature change
of the solution is recorded at regular intervals and can
be plotted on a graph
- Copper calorimetry, where a copper calorimeter is
placed over a spirit burner
...
This change in temperature is
recorded, as well as the change in mass of the spirit
burner (i
...
the mass of the fuel used)
- Bomb calorimetry, which uses a bomb calorimeter; a piece of equipment that minimises
heat loss and allows the reaction to take place in pure oxygen to ensure complete
combustion
The accuracy of calorimetry may be affected by;
- Heat being lost to a part of the surroundings that is not measured
- Incomplete reactions/combustion
- Loss of reactants (e
...
evaporation of a volatile substance)
- Non-standard conditions
Hess’ Law Hess’ law states that the enthalpy change of a reaction is
independent of the route it takes; the difference in chemical energy
between the reactants and products will always be the same
...
An enthalpy cycle can be used to determine

indirectly the enthalpy chance of reaction from the enthalpy change of formation and the
enthalpy change of combustion
...
It is measured in
moles per decimetre cubed per second
...
g
...
The gradient of the tangent to a point on the curve shows the rate of reaction at that
point in the reaction pathway
...

Factors affecting the rate of reaction include;
- Changes in temperature; at higher temperatures, molecules have more kinetic energy,
so collide more frequently and with more energy, increasing the chance of a successful
collision
- Changes in concentration; increased concentration means there are more molecules in
the same volume of a substance, so they are closer together
...
It does this by allowing the reaction to take place via a
different route with a lower activation energy
...
A homogeneous catalyst is catalyst used in a
reaction that is the same phase (state) as the reactants (e
...
enzymes)
...
The reactants adsorb to
the surface of the catalyst and the product molecules are later desorped
...
Catalysts are economically
important as they reduce the energy demands of reactions, thus reducing costs and
preventing environmental damage
Boltzmann distribution curve The Boltzmann distribution curve shows
the relationship between the distribution of
molecular energies within a same of a gas/
liquid at constant temperature
...
It
can illustrate how catalytic behaviour and
temperature changes can affect the

activation energy of a reaction
...
However, there
is no maximum energy a molecule can have, so the curve does not touch the energy axis
...
The area under the graph is equal to
the number of molecules and does not change in different conditions
...
The peak moves to a higher energy, but at a lower height
...


The introduction of a catalysts does not actually cause a change in the shape of the
distribution curve, but lowers the activation energy, so that automatically more particles
have sufficient energy to collide successfully
...
A system is closed when it remains isolated, so
that no materials are being added/removed and the external conditions remain constant
...
This
is done by changing the rates of forward and backward reaction
...
Equilibrium has shifted to the right
...
e
...
A decrease in temperature will cause a shift in equilibrium in the direction of
the exothermic reaction
Catalysts do not alter the position of equilibrium or the composition of an equilibrium
system
...
e
...


The Haber process highlights the issue of equilibrium vs yield
...
Using low temperatures would decrease the
rate of reaction as few nitrogen and hydrogen molecules would have sufficient activation
energy to react
...
It is also harmful to
the environment
...
An iron catalysts is also used to speed up the rate of reaction
...

The equilibrium constant Kc is the equilibrium constant in a homogenous dynamic
reaction and is used as an indication as to where the
position of equilibrium lies
...
It is calculated experimentally
...


A value greater than 1 means equilibrium lies to the right
...



Module 4: Basic concepts and hydrocarbons
Homologous series A homologous series is a series of organic compounds with the same functional group, but
each successive groups differs by a CH2 unit
...
They are detailed in either the suffix or prefix of a compound
...
g
...


(In order of increasing carbon atoms)
1
...
Ethane
3
...
Butane
5
...
Hexane
7
...
Octane
9
...
Decane
Naming branched compounds The stem (i
...
the main part of the name) is identified by identifying the parent chain
...


The prefix identifies other functional groups and the carbons they are attached to
...


‘Di-‘, ‘tri-‘ and ‘tetra-‘ are used to signify several of
the same functional group
...


General formula - The simplest algebraic formula for all the compounds in a homologous
series
Structural formula - Provides the minimum detail for the arrangement of atoms in a
molecule
Displayed formula - Shows the relative positions of atoms and the bonds between them
Empirical formula - Shows the smallest whole-number ratio of atoms of the elements in a
compound
Molecular formula - Shows the numbers and types of atoms in a compound
...
Lines are used to indicate alkyl chains, where every corner represents a carbon
atom
Hydrocarbons may be saturated (containing single covalent bonds only) or unsaturated
(containing at least one double carbon-carbon covalent bond)
...
This may be due to different arrangements of alkyl groups, different
placements of the functional group or different functional groups
Stereoisomers; organic compounds with the same molecular formula and structural
formula but different arrangements of atoms in space
E/Z isomerism; A type of stereoisomerism where there is restricted rotation around a
carbon-carbon double bond and different functional groups (substituents) attached to
each of the carbon atoms
...
If the highest
priority groups (i
...
the first atom have the highest atomic mass) are on the same side of
the carbon-carbon double bond the isomer is Z and vice versa
Cis-trans isomerism; A type of E/Z isomerism in which the two substituent groups
attached to both carbon atoms of the carbon-carbon double bond are the same and
each carbon atom of the double bond is attached to a hydrogen
...

Homolytic fissions occurs when each bonding atom receives one electron from the bonded
pair, forming two radicals
...

Heterolytic fissions occurs when one bonding atoms receives both electrons from the
bonding pair
...
This typically occurs due to
dipoles within the molecule
...

Covalent bonds form when two oppositely charged ions or two radicals collide
...
A
single headed arrow shows the movement of a single electron, whereas a double headed
arrow shows the movement of two electrons
...
Each carbon is bonded to four atoms in
a tetrahedral shape, with a bond angle of 109
...
They are all the same because
there is equal electron repulsion between every pair of bonded electrons
...
Two sp3 orbitals in
neighbouring carbon atoms overlap to form the carboncarbon sigma bond
...
A sigma bond is the end-to-end overlap of atomic
orbitals
...

As an alkanes carbon chain length increases, the relative molecular mass increases and
molecules have more surface area contacts between adjacent molecules
...
This is because more energy is needed to overcome this increased
attraction
...
This is why branched structural isomers have a lower
boiling point than the equivalent straight chain structural isomers
...
e
...
Due to the high levels of chemical energy stored in the covalent
bonds, alkanes make good fuels when they are combusted
...
During incomplete
combustion, where there is limited supply
of air, carbon particles, carbon dioxide,
water and carbon monoxide can be
produced
...

Alkanes undergo radical substitution in the presence of ultraviolet light with halogen
reagents (e
...
chlorine and bromine)
...

1) Initiation - the UV light causes
the formation of radicals via
homiletic fission
2) Propagation - The radicals
react with the reagents to
form ore radicals and
halogenation occurs
...
It is unpredictable

and difficult to control due to the reactivity of the intermediates formed, therefore creating a
mix of products which need to later be separated (e
...
by fractional distillation or
chromatography)
Alkenes Alkenes are unsaturated hydrocarbons containing a carbon-carbon double bond
...
However, the carbon-carbon double bond is made up of a sigma bond and a pi
bond, which involves the sideways overlap of adjacent carbons p-orbitals above and below
the plane of the carbon atoms
...
The double bond has the same effect on
shape as a single pair covalent bond in terms of electron repulsion, giving alkenes a
trigonal planar shape
...
This attracts electrophiles (species that are
electron-pair acceptors, such as cations)
...

Alkenes take part in electrophilic addition reactions;
- Hydrogenation to form alkanes at a temperature
of 150 degrees Celsius and in the presence of a
nickel catalyst
- Halogenation to form dihaloalkanes (e
...
bromine
water, which decolourises in the presence of an alkene because the bromine bonds to
the alkene)
- Halogenation using hydrogen halides to form haloalkanes
...
The major product can be decided using
Markownikoff’s principle, where more of the most
stable carbonation (i
...
has the most alkyl groups
attached, so a secondary carbocation rather than a
primary carbocation for example) will be formed
- Hydration using gaseous alkenes and steam at 300
degrees Celsius and 65 atmospheres in the
presence of a phosphoric acid catalyst to form
alcohols
Electrophilic addition reaction mechanism 1) The high electron density of the pi bond attracts
electrophiles, breaking the pi bond and causing
heterolytic fission of the bond within the
electrophiles molecule (if present)
2) This forms a positive carbonation intermediate,
which is extremely reactive, and an anion
3) The carbonation bonds to the negative ion that has been formed via heterolytic fission
Polymerisation Alkenes can also take part in addition polymerisation reactions
...
A repeating
unit is a specific arrangement of atoms that
occurs in a structure over and over again
...

The repeating unit can be generated by drawing the carbon-carbon double bond with
square brackets around it
...

Polymers are extremely stable and thus non-biodegradable in landfill sites
...

Polymer waste can be dealt with by combusting waste products for energy reusing them
(e
...
as organic feedstock for the production of plastics and other organic chemicals) and
recycling
...
g
...
Recycling is a laborious process and only a degree of the polymers can be
used again
...

Bioplastics are biodegradable polymers that contain plant starch molecules
...
The bonds within the structure are weakened by the absorption of
these wavelengths, initiating an irreversible degradation of the polymer
...
This makes them polar molecules that can dissolve in polar substances
...

A primary alcohol has the alcohol group attached to an end of a chain
...

A tertiary alcohol has the alcohol group attached to a carbon attached to three alkyl
groups
...
The boiling point of
alcohols are higher than that of corresponding alkanes because there are also hydrogen
bonds between the -OH groups
...
Volatility is how easily a substance evaporates and increases
when boiling point decreases
...

The miscibility of the alcohol therefore declines
...
They
transfer stored chemical energy in their bonds into thermal energy


- Oxidation

Primary and secondary alcohols can be oxidised using the oxidising agent potassium
dichromate and a strong acidic catalyst (e
...
dilute sulphuric acid)
...
They can also be oxidised into carboxylic acids under reflux conditions, where
the reagents are heated strongly with excess potassium dichromate and the product is
not distilled immediately (as distillation prevents any further reaction from occurring);
reflux is the constant boiling and condensing of a reaction mixture
...
Tertiary alcohols cannot be oxidised
...
If there is
no colour change the alcohol is tertiary
...
When added to a heated
and distilled alcohol there may be a colour change; this indicates that the alcohol is a
secondary alcohol
...
They are fragrant and
small molecules can be powerful solvents
...



Esterification is the elimination of a water molecule from reacting an alcohol and a

carboxylic acid in the presence of a concentrated acidic catalyst (e
...
phosphoric acid)
...

Only small molecule esters are soluble in water, so an oil layer forms which can be
tapped off from the aqueous layer, or the product mixture can be distilled on a large
scale
...

The alcohol is heated under reflux with a strong acid catalyst to remove the -OH group
and a H atom from the adjacent carbon, causing a pi bond to form between the two
carbon atoms
...
g
...
The
reaction takes place in the presence of a strong acidic
catalyst under heating to increase the rate of reaction
...

Haloalkanes Haloalkanes are saturated organic compounds containing carbon, hydrogen and at least
one halogen atom
...

The big difference in
electronegativities of the carbon
atom and halogen atom means that
the bond is very polar, which attracts
nucleophiles to the delta positive
carbon atom
...
This results in nucleophilic substitution, where the nucleophile
replaces a group of atoms - in this case the halogen atom
...


The reactivity of the reaction is determined by the polarity of the C-X bond (which
decreases down the group) and the strength of the C-X bond
...
e
...
This is
because there is less electron shielding
...
An
ethanol solvent is used to allow the water
and haloalkane to mix, rather than separating
...

Chlorofluorocarbons (CFCs) are organic compounds containing both chlorine and fluorine
atoms
...


However, when they rise to the stratosphere they are exposed to UV light, causing their
homolytic fission
...
Ozone (triatomic oxygen) is also located
in the stratosphere and absorbs UV-B and UV-C rays (i
...
the high energy UV rays)
...


Nitrogen oxides (e
...
nitrogen monoxide) formed during high temperature combustion of
fuels can also form radicals, which deplete the ozone
...

Infrared radiation causes covalent bonds to vibrate more as they absorb energy, with
either a stretching or bending motion
...

A beam of infrared radiation is passed through the sample
...
The
frequency is measure using wavenumber (per cm)
...
Each molecule has a unique fingerprint region of the
spectrum that can be used to compare the spectra to previously published spectra
...

Infrared spectroscopy can be used to monitor gases causing air pollution and in
breathalysers, as they detect the -OH group in ethanol
...

The organic compound is vaporised and driven through a mass spectrometer, causing the
molecules to be ionised by losing an electron
...
Although it is a
destructive analytical technique, it can be
used to analyse very small quantities very
accurately and relatively cheaply
...

The original molecular ion breaks up into positive fragment ions and neutral species
...
These
fragment ions can be detected by a mass spectrometer
...
The fragmentation patterns are then analysed to determine
the structure of the compound
...


Practical skills in chemistry -

- Quickfit apparatus; heat resistant glassware
that can be easily fixed together in variety of
arrangements
...



- Distillation; a technique used to
separate miscible liquids or
solutions
...
Anti-bumping granules
are added to the organic
mixture in the round-bottomed
flask to ensure smooth boiling
...



- Reflux; a technique used to stop a reaction mixture boiling
away into the air
...



- Using a separating funnel; this is used to separate
immiscible organic compounds that may appear as an
aqueous layer and oily organic layer
...
A stopper is placed in the funnel, and the
funnel is inverted then replaced and left so the layer
separate
...
The
desired organic product can then be collected in a separate beaker
...
This is then filtered using gravity filtration to collect the dry
organic product
...
A positive result decolourises the bromine water from
orange
...
The colour of the precipitate indicates the halide
ion present
...



- Carbonyl

Add acidified dichromate
...


OR

Add Fehling’s solution
...


OR

Add Tollens’ reagent
...



- Carboxylic acid

Use universal indicator or a pH probe
...


OR

Add a reactive metal
...


OR

Add a metal carbonate, which cause effervescence from the production of carbon
dioxide, which will turn limewater cloudy when bubbled through it
...
This should
create a sweet smell as an ester is formed
...
It can be measured by
determining changes in pH, changes in volume/pressure/mass or visible changes, such as
precipitate formation or colour changes (using colorimetry and clock reactions)
...

Initial rate of reaction is the rate of reaction when time equals 0, and is proportional to 1/t
...
It can only be determined from experimental data,
where the concentrations of the reactants are varied and the changes in rate of reaction
are recorded
...
The units of k are determined by
substituting units for rate and concentration into the rate equation, and are dependent on
the overall order of the rate reaction
...



















Order with respect to a reactant The power to which the concentration of the reactant is raised in the rate equation
...
The
overall order is the sum of m + n
...
The half
life decreases with time
...
The half life remains
constant, so the value of the half life can be used to determine the value of the rate

constant
...

Rate determining step A reaction mechanism is a series of steps that make up an overall reaction
...
Within a reaction mechanism there is the rate-determining
step; the slowest step
...
The order attached to a
reactant in the rate equation is equal to the number of molecules of that reactant involved
in the rate determining step
...


This can be rearranged to give;

The rate constant and equilibrium The equilibrium law states;

A homogenous equilibrium is an equilibrium in which all the species making up the
reactants and products are in the same physical state,
whereas a heterogeneous equilibrium occurs when the
species are in different physical states
...
The
concentration of reactants and products can be
determined through titrations or by comparing the colour
intensity of the mixture to a known concentration using
colorimetry
...
The initial concentration, equilibrium concentration and change
in concentration of either a product or reactant is used to find the change in concentration
of another reactant/product
...
The units for Kc are
dependent on the molar ratios of products and reactants, so need to be calculated for each
reaction
...
As a result, the concentration of pure
liquids and solids are not included in the Kc equation, but rather only gases and aqueous
substances
...
Round brackets are used to donate partial
pressures
...
It is calculated by multiplying total pressure of the system by the mole
fraction of the species
...

The concentration of a substance is proportional to its partial pressure
...

When K is greater than 1, the product side is favoured, whereas when K is less than one
the reaction is reactant-favoured
...
If
the forward reaction is endothermic and temperature increases, K also increases
...

The value of K is unaffected by changes in concentration and pressure, because shifts in
equilibrium position will counteract the changes to restore the original K value
...
In short, only temperature affects the value of K
...
A
Bronsted-Lowry base is a proton acceptor
...
Conjugate acid-base pairs are two species related to each other by the
loss or gain of a proton (i
...
they only have a H ion difference)
...
g
...
This is the definition for Arrhenius acids and bases, but cannot be used
for non-aqueous solutions and non-soluble bases
1916; Lewis

Described a (Lewis) acid as an electron-pair acceptor and a (Lewis) base as an
electron-pair donor
1929; Bronsted-Lowry

Proposed that acids were proton donors and bases were proton acceptors
...
A dibasic acid can release two
protons at different stages and a tribasic acid can release three protons at different stages
...
Strong acids include hydrochloric acid, nitric acid, sulphuric acid, hydrobromic
acid, hydroiodic acid and chloric(VII) acid
...
This
involves a dative covalent bond between the proton and
water molecule, giving the overall ion a positive charge
...

Neutralisation is the chemical reaction in which an acid
and base react to produce a salt and water
...


The acid dissociation constant The acid dissociation constant (Ka) can be used to measure the extent to which an acid
dissociates
...
A small Ka value indicates little dissociation,

meaning the acid is weak
...

A low Ka value corresponds to a high pKa value, whereas a high Ka value corresponds to
a lower pKa value
...

Because the concentration of hydrogen ions in a solution can vary
greatly, the logarithmic pH scale is used to denote these
concentrations
...
A low pH value indicates a high concentration of hydrogen ions (i
...

The pH of a strong monobasic acid is approximately equal to the concentration of the acid
...

It is assumed that;
- The concentration of hydrogen ions is equal to that of negative ions
- The concentration of the undissociated acid is approximately equal to the concentration
of the weak acid at equilibrium
...
As an acid it dissociates into a hydrogen ion
and hydroxide ion
...


The back and forth transfer of protons happens so that water exists at equilibrium
...


In pure water, the concentration of the two ions are equal
...

At room temperature and pressure, Kw is equal to 1
...
For strong monobasic
alkalis, the concentration is assumed to be equal to that of hydroxide ions
...

Buffer solutions:
A buffer solution is a mixture that minimises pH changes on addition of small amounts of
acid or base
...
The weak acid removes added alkali and the conjugate
base removes added acid to restore equilibrium
- Excess of a weak acid and a strong alkali so that
partial neutralisation occurs


Rearranging Ka can be used to calculate the pH of a
buffer solution
...
The buffer is only effective when there
are equal concentrations of the weak acid and its conjugate base, so that the pH of the
buffer solution is within two units of the pKa value of HA
...
2 and
7
...

Excess carbonic acid are removed by being converted into aqueous carbon dioxide by
enzymes and then expelled via expiration
...
On a titration curve showing
an acid-base titration against pH, the equivalence point is the
centre of the vertical section
...
This weak
acid has one colour in its acid form (HIn) and another in its
conjugate base form (In-)
...
The colour at the end point is midway between the colours of the weak acid and
conjugate base
...


Strong acid-strong base

Vertical section ranges from pH 3-11

Equivalence point at 7

Methyl orange and phenolphthalein may be used

Weak acid-weak base

No real vertical section
No indicators are suitable for this titration

Weakacid-strong base

Vertical section ranges from pH 6
...
5
Equivalence point is above 7

Phenolphthalein may be used

Strong acid-weak base

Vertical section ranges from pH 3-7
...
It is an exothermic
process, so has a negative value
Standard enthalpy change of formation - The enthalpy change that accompanies the
formation of one mole of a compound from its constituent elements in their standard states
Standard enthalpy change of atomisation - The enthalpy change that accompanies from
the formation of one mole of gaseous atoms from its element in its standard state
...
It is an endothermic process
Second ionisation energy - The energy change that accompanies the removal of one mole
of electrons from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions
First electron affinity - The energy change when one mole of gaseous 1- ions is formed
from one mole of gaseous atoms
...
It is an endothermic process because the electron
overcomes the repulsion from the negatively charged ion
Standard enthalpy change of solution - The enthalpy change that takes place when one
mole of a solute is completely dissolved in a solvent under standard conditions
...
This is an exothermic process
Lattice enthalpies can’t be measured directly because it is impossible to form one mole of
solid ionic substance from its gaseous ions
...
In a Born-Haber cycle there is a continuous cycle that includes one step
to show the lattice enthalpy and the remaining steps show intermediate changes to form
the ionic solid from its elements
...
In Born-Haber cycles
the datum line is used to
represent the elements in their
standard states (i
...
with no
energy)
...
Energies must be
doubled when there are two
moles involved in a process
...
This
is why ionic substances have
very strong ionic bonds and
very high melting/boiling

points
...

The smaller the radius of the ion, the greater the ionic bond strength and the larger the
charge of ions, the greater the magnitude of the lattice enthalpy
...
Ions
with larger charges also have
greater attraction
...

Likewise, with enthalpy changes
of hydration, smaller ions with
larger charges can interact more
with the water molecules, so the
enthalpy change of hydration is
more exothermic
...
This is not always the case due to
temperature and entropy
...
Above 0K entropy is always a positive number because they are
thermodynamic and in constant motion
...
The total
entropy of a reaction is the sum of the entropy of the system and the surroundings
Standard entropy change of reaction - The entropy change that accompanies a reaction in
the molar quantities expressed in a chemical equation under standard conditions, all
reactants and products being in their standard states
...
g
...
It is measured by the sum of the entropy of the products minus the sum of
the entropy of the reactants
Free energy change - The balance between enthalpy, entropy and temperature for a
process; it is equal to the enthalpy change minus the product of temperature and entropy
change
...
Their arrangement thus
becomes more random
...

Examples of entropy increasing include water evaporating to water vapour and ionic
substances dissolving in water
...
If it
leads to a decrease in gas molecules, there is a decrease in entropy
...
If it becomes more ordered, entropy
decreases
...
If the free
energy change is greater than
zero, the reaction is not
feasible and wont occur
spontaneously
...
It may also have an extremely
low rate of reaction that isn’t visible (e
...
graphite forming into diamond)
...
The number of electrons lost in the oxidation half-equation
is always equal to the number of electrons gained in the reduction half-equation
...


Redox titrations can be used to determine the amounts of species being oxidised or
reduced
...

Many redox species are self-indicators and change colour between oxidation states, so an
indicator need not be used
...
It
goes from deep purple to colourless when it is reduced from +7 to +2 oxidation states
...
Mandate is
usually acidified
...


- Iodine is blue-black in the presence of starch,
but when it is reduced to its ions it is
colourless
...
Aqueous
iodide and aqueous thiosulfate ions can be used to determine the concentration of an
unknown reducible species
...
The liberated iodine reacts with the thiosulfate ions
...
This makes it easier to identify the end
point, however if the
starch is added too
early, an insoluble
iodine-starch complex
may be formed
...
The copper solution is mixed with aqueous iodide ions
...
This precipitate may
appear light brown due to the iodine
...
When the iodine reacts, the mixture becomes paler
...

For alloys, such as brass and bronze, the substance is first reacted with nitric acid to
produce a solution containing copper(II) ions
...

They are used to utilise electrical energy in batteries and
cells
...
For
example, a metal place in an aqueous solution of its ions
...
A platinum electrode is used to connect the half cells
...

Hydrogen half cells are
connected using a
platinum electrode
coated with platinum
black; it is inert but
allows the passage of
electrons into and out
of the half cell by a
connecting wire
...

The direction of
electron flow is dependent on the relative tendency of each electrode to release electrons
...

A half cell is connected to a hydrogen half cell,
which usually has an e
...
f
...
They are
connect by a wire to carry electrons and a salt
bridge to allow the transfer of ions
...

Half cells can be ordered by their standard
electrode potential to form an electrochemical
series
...
A positive value
indicates the forward reaction is favoured
...
One half cell will gain electrons, the other will lose electrons
...

The half cell with the lower electrode potential, so will release electrons more readily at
equilibrium
...
Electrons flow through the wire
into the positive electrode
...

The bigger the reading on the voltmeter, the bigger this shift in equilibrium
...
A positive electrode potential indicates the reaction is feasible
...

There are limitations to using standard electrode potentials;
- Non-standard conditions (such as different concentrations) alter electrode potentials, as
they may shift equilibrium, therefore making the electrode potentials invalid
- Actual conditions of a reaction may be different to standard conditions (e
...
not in
aqueous solution)
- The reaction may have a high activation energy and slow rate of reaction
Uses of half cells:
- Non-rechargable cells; react until they react to a point where the voltage falls
- Rechargable cells; the chemicals in the cells can be regenerated, for example nickelcadmium and lithium-polymer batteries
- Fuel cells; the cell reaction uses an external energy source and oxidant that need to be
supplied continuously for the cell to function
...
g
...
They use energy from the
reaction of a fuel with
oxygen
...

There are risks to using
electrochemical cells
such as toxicity and the
potential to causes fires/
explosions
...
Zinc and scandium are not transition elements because their d-sub shells are not
partially filled
...
In
chromium the five 3d orbitals
and the 4s orbital all contain
only one electron
...
This reduces
repulsion in the outer electrons
to increase stability
...


Transition metals have the same physical properties as metals; they are lustrous, have
high densities, high melting points and
high boiling points
...

The compounds of transition metals form
coloured solutions when dissolved in
water
...
The colour of the
dissolved compound they make can be
used to determine which oxidation state
the transition metal is in
...
Potassium
dichromate(VI) has chromium in its
highest oxidative state; +6 and has
is an organ crystalline solid
...


Transition elements can be used as catalyst, due to their partially filled d-orbitals
...
They are desorbed after the reaction, leaving the metal unchanged
...

Transition element catalysts can be toxic and thus must be disposed of carefully when they
no longer function (i
...
their active sites are binded to by a substance)
...
A ligand is a molecule/ion
that can donate a pair of
electrons to the transition metal
ion to form said coordinate bond
...
In a mono dentate ligand, the ligand donates just one pair of
electrons
...
EDTA
(ethylenediaminetetraacetic acid) is a multidenate ligand that can donate 6 pairs of
electrons and form the EDTA4- ion
...
It is used in
detergents to reduce water hardness, food to stabilise ions that may catalyse oxidation
and medicine to prevent blood sampling from clotting in patients with lead/mercury
poisoning
...

In the formula of a complex ion the square brackets groups together
the species making up the complex ion, and the overall charge is
shown outside these brackets
...
Four of the ligands are on the
same plane, one is above and one is below
...

Complex ions with four-fold coordination form a tetrahedral shape or, more rarely, a square
planar shape when there are four mono dentate ligands in the same plane
...
The purple
isomer is the ‘cis’ isomer when the
two Cl- ligands are at 90 degrees to
one another at adjacent corners of
the octrahedron
...

Another example which includes a
complex ion with bidenate ligands is
the diaquadioxalatochromate(III) ion
...

Cis-platin is the cis isomer of the
platinum complex
dichlorodiamineplatinum(II) and is used
to treat cancer in medicine
...

Octahedral complexes that contain multidentate ligands can form optical isomers when;
- A complex with three molecules or ions of a bidentate ligand
- A complex with two molecules or ions of a bidentate ligand and two molecules or ions of
a monodentate ligand
- A complex with one hexadentate ligand

Ligand substitutions Ligand substitution is a reaction in which one ligand in a complex ion is replaced by
another ligand
...

1) Aqueous copper(II) ion and ammonias

Aqueous copper(II) ions have a pale blue colour that changes to deep blue when
excess ammonia is added
...
The product has a distorted octahedral shape (it is distorted because the
copper to oxygen bonds are greater than the copper to ammonia bonds)
...
This precipitate dissolves upon the addition of excess ammonia to form a
dark blue solution
...
Adding water reverses the reaction
...
This is because the chloride ligands are larger and therefore have
stronger repulsion; fewer can fit around the central ion
...












3) Aqueous chromium(III) and ammonia

Aqueous chromium(III) ion complexes have a grey-green/dark green colour
...
When excess ammonia is added, some of the
green precipitate dissolves to form a dark green solution of hexaamminechromium(III)
...

Dichromate(VI) can be reduced to chromium(III) ions by acidifying and adding zinc
...
In the presence of excess zinc the chromium(III)
ions are further reduced to chromium(II) ions, which have a pale blue colour
...

When aqueous copper(II) reacts with excess iodide ions a white precipitate of copper(I)
iodide is formed
...
This is a
disproportionation reaction
...
Oxygen reversibly binds to iron(II) to give the haem group a red
colour
...
Oxygen can form
a final coordinate bond when the molecule passes through the lungs
...
However, this reaction is not reversible, so the
red blood cell loses its function
...

Iron(II) is less stable than iron(III), so in the presence of air/an oxidising agent, it readily
oxidises to iron(III)
...


Redox reactions, such as those between iron(II) and acidified manganate(VII) can be used
to calculate the percentage of a transition metal ion in an unknown solution
...

Potassium dichromate(VI) also oxidises iron(II) ions in solution
...

Identifying ions Precipitate reactions can be used to identify ions in solutions
...

An aqueous solution of ammonia or sodium hydroxide is added drop by drop
...
Sodium
hydroxide is added and the mixture is warmed gently
...

Carbonate ions react with acids to produce carbon dioxide, which can be collected and
pass through limewater
...

Sulfate ions react with barium ions to form the insoluble salt barium sulfate
...
A positive result produces
a white precipitate
...
The colour of the precipitate indicates the halide ion present
...



Module 6: Organic chemistry and analysis
Benzene Benzene is a naturally occurring aromatic hydrocarbon
...
It has a molecular formula of C6H6 and an empirical formula of
CH
...


Kekule suggested benzene was a six-membered carbon ring with alternating single and
double bonds between carbon atoms
...
Kekule believe benzene was in
dynamic equilibrium where the double bonds
and single bonds continually switched
positions
...
Benzene also does not decolourise bromine water

- The enthalpy of hydrogenation of benzene shows it is more stable than predicted
...
However, the enthalpy of hydrogenation for benzene is actually
-208 kJ/mol
The six carbon to carbon bonds all have the same length, which has been discovered
using X-ray diffraction techniques
...
135 nm and carbon-carbon single bonds would have a length
of 0
...
However, benzene carbon to carbon bonds all have a length of 0
...
This
states benzene is a planar, cyclic, hexagonal hydrocarbon, where each carbon atom has
one electron in a p-orbital at a right angle to the plane of the bonded carbon and hydrogen
atoms
...
These electrons form a ring of delocalised electrons above and
below the plane of the molecule
...
The overlapping p-orbitals creates a system of pi-bonds, which spread all
over each of the carbon atoms
...

More energy is needed to disrupt the delocalisation, so benzene is more stable and
resistant to addition reactions
...

Aromatic compounds contain one or more benzene rings
...
The
compound is named using the longest carbon chain as the stem and the group attached
as the prefix (e
...
ethylbenzene)
...
The same naming principle is used, however the groups are
given a number; the carbon that they are attached to
...

This occurs with multiple substitutions as well
...

Reactions of benzene Benzene goes through electrophilic substitution reactions where an electrophile is
attracted to an electron-rich atom and a new covalent bond is formed by the electrophile
accepting an electron pair
...

1) Electrons above and below the plane of atoms in the benzene ring attract an
electrophile
2) The electrophile accepts a pair of pi electrons from the ring and forms a covalent bond
(this is the rate-determining step)
3) A reactive intermediate is formed where the delocalised electrons have been disrupted;
this intermediate is unstable, so release a hydrogen ion to form a stable product

Nitration is an example of an electrophilic substitution involving benzene
...
The reagent is concentration nitric acid with a concentrated
sulfuric acid catalyst
...
Benzene is added and refluxed at a
temperature of 50 degrees Celsius to prevent further substitution
...

This means benzene has a lower
electron density between carbon
atoms than an alkene, so cannot
induce a dipole great enough to start
the substitution reaction
...
This can be iron, iron halides or
aluminium halides
...
For example, for
chlorination, aluminium chloride or iron chloride may be used and for bromination
aluminium bromide or iron bromide may be used
...
The halogen carrier is a catalyst so regenerates using the related hydrogen
ion
...
The carbon to hydrogen bond is broken and replaced with a carbon to
carbon bond (known as alkyation or acetylation)
...
This reaction can
occur at room temperature
...
There
will be multiple substitutions, so many products which need to be separated by fractional
distillation will be made
...

























- Acyl chloride

An acyl chloride has the functional group RCOCl
...
The acyl chloride is used as the halogen carrier to
substitute just one hydrogen atom
...
The catalyst is a strong Lewis
acid catalyst
...
Phenol is the first member of
the group
...

Phenol is a weak acid, as it partially dissociates
in water
...
It does not react with carbonates and
weak bases
...

This increases the electron density of the aromatic ring, making it more susceptible to
electrophilic attack as it can induce dipoles in non-polar molecules more easily
...


Phenol will undergo a triple substitution with bromine water at room temperature, resulting
in a white precipitate of 2,4,6-tribromophenol
...
Unlike nitration with
benzene, this does not require a
concentrated acid catalyst
...

In phenol, the additional
electrons from the oxygen into the pi-electron
system make the reactions occur on the 2
and 4 positions of the aromatic ring
...
Other
electron-donating groups such as amine
groups also have 2- and 4-directing effects
...

Electron withdrawing groups such as nitro
groups have a 3-directing effect
...

This is important as it can be used to create a
reaction pathway that maximises the yield of
a desired product
...

Aldehydes undergo oxidation using
potassium dichromate and sulfuric acid
under reflux to form carboxylic acids
...
Carbonyls have a dipole in the carbon to oxygen double bond, making
them susceptible to nucleophilic attack on the delta positive carbon atom
...


Sodium tetrahydridoborate(III) (NaBH4) is a reducing agent
...
When added to a carbonyl group
they form alcohols
...

Hydrogen cyanide is a weak acid that
partially ionises to form a hydrogen ion and
cyanide nucleophile with a negative charge
on the carbon atom
...
Addition of cyanide allows
further carbon atoms to be added to an
organic molecule and also forms
hydroxynitriles
...
When mixed
with methanol and sulphuric acid, it creates Brady’s reagent; a transparent orange mixture
...


The precipitate can be collected by filtration and purified using recrystallisation
...

However, ketones have similar chain lengths and therefore similar melting points, so it can
be difficult to identify them accurately
...
It is a weak oxidising agent, so reacts with aldehydes but not
ketones
...
This is because the silver ions are reduced and the aldehyde group is
oxidised to a carboxylic acid
...

Carboxylic acids Carboxylic acids have the functional group -COOH
...

- They react with metals to form metal salts with the suffix -oate (instead of -oic acid) and
hydrogen
- They react with metal oxides (a type of base) to make a metal salt and water
- They react with metal hydroxides (a type of alkali) to form a metal salt and water
- They react with metal carbonates (a type of base) and metal hydrogencarbonates to
form a metal salt, carbon dioxide and water
...
Solubility decreases as size increases
because the proportion of the molecule that is non-polar increases, as the only the
functional group can form hydrogen bonds
...
They are
carboxylic acid derivatives, where the H has been
replaced by an alkyl chain
...
g
...


Esterification can occur by;

- Reacting a carboxylic acid with an alcohol by heating gently in the presence of a
sulphuric acid catalyst
...
The ester can be separated
quickly using distillation to prevent the reverse reaction from occurring
...




























- Reacting an acid anhydride (made by the condensation of two
carboxylic acids) with an alcohol
...








Esters can also be hydrolysed
...


In acidic conditions the ester is refluxed with a hot dilute strong acid to form an alcohol and
carboxylic acid
...
Alkaline hydrolysis is known as saponification
...
Small acyl
chlorides are fuming colourless liquids and very reactive
...



Acyl chlorides can be made by using SOCl2 at room temperature to substitute the hydroxyl
group of the carboxylic acid
...

Reactions of acyl chlorides;

- They react with alcohols and phenols to form esters
...


- They react with water to hydrolyse to produce carboxylic acids
...


- They react with concentrate ammonia solution to form primary amides and ammonium
chloride
...

Amines Amines are class of compounds related to
ammonia; one or more of the hydrogens has been
substituted for an alkyl chain
...

Secondary amines have two hydrogen atoms
substituted so that the structural formula is RNHR’
...

Amines have the suffix
amine and the stem and
prefix are determined by
the alkyl chain
...

Amines and ammonia act as weak bases; they have a lone pair of electrons on the
nitrogen atom that can be donated and can accept protons
...

When amines react with dilute inorganic acids (e
...
HCl) they form alkyl ammonium salts
(i
...
alkyl ammonium
chloride)
...

Alkyl ammonium ions have a single positive charge, so two ions are needed for every
sulphate ion
...

The reagents are a haloalkane, excess ammonia and ethanol in a sealed tube (not under
reflux, as the ammonia is so volatile it would escape the condenser)
...
This is because amines have lone pairs of electrons on the
nitrogen which act as a nucleophile
...


Aromatic amines can be produced using nitroarenes (such as nitrobenzene) using a
mixture of tin and concentrated hydrochloric acid under reflux at 100 degrees Celsius
...
After half an hour excess strong sodium hydroxide is added
to neutralise excess acid and produce an amine
...


Amino acids An alpha amino acid is a compound with a carboxylic acid group and amine group
attached to the same carbon atom
...

This makes amino acids amphoteric (acting as both and acid and base)
...
The two charges cancel each other out, so the molecule has no
overall charge; this occurs at the isoelectric point (pH)
...
In alkaline conditions, the carboxylic acid group donates a
proton, resulting in the ion having an overall negative charge
...
The
carboxylic acid reacts with bases to form salts and alcohol to form esters
...

Amides An amide is a class of compound made up of an acyl group attached directly to an amine
...


A primary amide has the nitrogen atom attached to two hydrogen atoms and one acyl
group
...
A tertiary amide has a nitrogen atom with no hydrogens attached
...
The bonding of
monomers occurs between the carboxylic acid and amine of adjacent molecules
...
This carbon atom is labelled 1
...

Optical isomerism Optical isomers are molecules which are nonsuperimposable mirror images of each other
...
They are a type of stereoisomers
and each isomer is known as an enantiomer
...
If it rotates the
plane clockwise, the prefix is ‘+’, if it rotates the plane anticlockwise, the prefix is ‘-‘
...
A racemic mixture occurs when there is a 50:50
mixture of enantiomers, causing no overall effect on the polarised light
...
It is known as the chiral centre and illustrated with a ‘*’
...

Polymerisation There are two types of polymerisation;
- Addition polymerisation, where monomers have at least one carbon to carbon double
bond that breaks and joins the monomers together


- Condensation polymerisation; this is the
chemical reaction to form a long-chain
molecule by elimination of a small molecule,
such as water
...

If a molecule have both a carboxylic acid group and alcohol group they can form a
polyester from just that one monomer
...
When a polyester is reacted with a
strong aqueous acid the reaction produces a
diol and dicarboxylic acid
...
The rate of basic reaction takes place
with hot sodium hydroxide solution to produce
a diol and the salt of a dicarboxylic acid
...

Polyamides are a class of condensation polymer made by reacting a dicarboxylic acid with
a diamine, forming an amide (R-CONH-R’) link between the two molecules
...


Polyamides can also undergo hydrolysis in acidic and basic conditions
...

When a polyamide is reacted with
strong aqueous acid it produces a
dicarboxylic acid and diammonium
salt
...


Nitriles Nitriles are organic compounds with the -CN functional group
...

This can be done used the cyanide ion (nitrile group)
...

Potassium cyanide and a haloalkane are mixed and heated under reflux
...
The cyanide
ion (nucleophile) attacks the delta positive carbon of the haloalkane and nucleophilic
substitution takes place
...
The carbon on the carbonyl group has a delta positive charge, so
attracts the cyanide ion
...
This can accept the proton to form a
hydroxyl group
...

The carbon to oxygen double bond is planar, so the cyanide ion may attack from either
side
...

As hydrogen cyanide is highly toxic and stops mitochondrial enzymes working, safer
alternatives such as acidified potassium cyanide are used
...
This
can be done by using;
- Hydrogen gas, which can react directly with a
nitrate to form a primary aliphatic amine; the two hydrogen atoms are added to the
nitrogen atom
...

Nitriles can undergo hydrolysis to form an ammonium
salt via an amide
...
The
organic acid is formed, rather than an organic
ammonium salt, because the strong acid fully dissociates
...


Practical skills Filtration under reduced pressure

This is used to purify an organic solid
...
Filter
paper is placed into the top of the funnel
...

2) Turn the vacuum pump on and pour the reaction mixture into the funnel
...

4) Rinse the collected solid with more solvent and maintain suction for a minute after all
the washings have been added
5) Turn off the suction and collect the organic solid by inverting the funnel onto a watch
glass
...
If the product
is coloured, heated charcoal can be used to remove coloured impurities
...
The hot filtrate is cooled until crystallisation
occurs
...

3) The purified organic product can be collected by vacuum filtration
...

- Melting point apparatus can be used; a few grains of the organic solid are added to a
sealed capillary tube and inserted into the machine next to an accurate thermometer
...

- A thiele tube can be used; a few grains of the organic solid are added to a sealed
capillary tube
...
The thermometer is submerged
into the oil of the thiele tube, and a micro burner is used to heat the side arm of the
thieve tube
...


Analysis Chromatography is a separation technique used to identify chemicals in a mixture
...
This is a liquid in gas chromatography
systems and solids in thin layer chromatography (TLC)
- The mobile phase, which moves in a definite direction
...

Thin layer chromatography is used to determine the purity of a sample
...
g
...
g
...
The mobile phase is an organic solvent, which moves vertically
upwards
...
The values are compare to
data bases to identify substances
...
The stationary
phase is a solid or liquid coating containing a hydrocarbon with a high boiling point on a
coiled tube (i
...
the liquid is adsorbed onto a solid surface)
...

A gas chromatogram shows retention time (the time taken for a component to travel from
the inlet to the detector) against absorption
...
The area under each absorption peak is
proportional to the concentration of each component
...

Nuclear magnetic resonance is a non-destructive analytical technique used to confirm the
formula mass and structure of a chemical
...
1H is dissolved in a solvent containing deuterium (2H isotope), as this makes
the solvent ‘heavy’ and produce different signals to the 1H isotope
...
When put in a large magnetic field, the direction of
the spin of the nucleons aligns with the direction of the
magnetic field
...
Resonance is measured using chemical
shift, in units of parts per million
...
Chemical shift is given the
symbol delta and is measured in parts per million (ppm)
...
The lower the chemical shift values, the more
similar the carbon and protons are to TMS, which is symmetrical and non-polar
...

This gives information about the
number of carbon environments and
potential functional groups attached,
but not the ratio of atoms in each
environment
...

Carbon atoms in the same
environment are known as
equivalents
...
Two carbon atoms
positioned symmetrically within a
molecule are equivalent
...
This gives
information about the number of proton environments and the area under each peak gives
the ratio of protons in each environment
...

TMS gives an intense single peak at 0 ppm, because it has 12 equivalent protons
...
Neighbouring protons affect the magnetic field of the protons,
causing a split in the signal
...
e
...
It reacts identically to water in reactions, but has different physical
properties
...
An odd number of nucleons is needed to produced a signal



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