Search for notes by fellow students, in your own course and all over the country.

Browse our notes for titles which look like what you need, you can preview any of the notes via a sample of the contents. After you're happy these are the notes you're after simply pop them into your shopping cart.

My Basket

Buy These Notes

You have nothing in your shopping cart yet.

Title: Edexcel A2 Chemistry revsion notes
Description: made during revision of A2 exams. contains detailed revision notes for both unit 4 and 5 edexcel chemistry made from both revision guides and textbook and lesson notes. questions and model answers from past papers jan 2010- jan 2015. included also specification specific notes with answers to each specific point to the specifications, concise version of revision notes. total 69 pages.
Buy These NotesPreview

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

Edexcel

A2 Chemistry

Revision Notes

A2 CHEMISTRY
UNIT 4 ------------------------------------------------------------------------------------------------------------------------------- 3
How fast? – Rates ----------------------------------------------------------------------------------------------------------------- 3
Rate of reaction ---------------------------------------------------------------------------------------------------------------- 3
Activation energy and catalysis -------------------------------------------------------------------------------------------- 4
Mechanisms and rate-determining steps -------------------------------------------------------------------------------- 4
How far? –entropy---------------------------------------------------------------------------------------------------------------- 6
Entropy --------------------------------------------------------------------------------------------------------------------------- 6
Feasibility, stability and inertness ----------------------------------------------------------------------------------------- 7
Enthalpy changes and dissolving ------------------------------------------------------------------------------------------- 8
Equilibria ---------------------------------------------------------------------------------------------------------------------------- 9
Equilibrium mixtures ---------------------------------------------------------------------------------------------------------- 9
Gaseous equilibria and Kp---------------------------------------------------------------------------------------------------- 9
More on equilibrium constants -------------------------------------------------------------------------------------------10
Rates and equilibria in industry -------------------------------------------------------------------------------------------11

Acid/base equilibria ------------------------------------------------------------------------------------------------------------12
Acids and bases ---------------------------------------------------------------------------------------------------------------12
pH and dissociation constants ---------------------------------------------------------------------------------------------12
Titration curves, indicators ad buffers -----------------------------------------------------------------------------------13
Further organic chemistry -----------------------------------------------------------------------------------------------------15
Isomerism, chirality and optical activity ---------------------------------------------------------------------------------15
Aldehydes and ketones -----------------------------------------------------------------------------------------------------15
Reactions of carbonyl compounds----------------------------------------------------------------------------------------15
Reduction of aldehydes and ketones ------------------------------------------------------------------------------------16
Carboxylic acids ---------------------------------------------------------------------------------------------------------------17
Esters and polyesters --------------------------------------------------------------------------------------------------------18
Acyl chlorides ------------------------------------------------------------------------------------------------------------------19
Spectroscopy and chromatography -----------------------------------------------------------------------------------------21
Spectroscopy ------------------------------------------------------------------------------------------------------------------21
UV, mass spectra and chromatography ---------------------------------------------------------------------------------22

1

Edexcel

A2 Chemistry

Revision Notes

UNIT 5 ------------------------------------------------------------------------------------------------------------------------------23
Redox and the chemistry of the transition metals -----------------------------------------------------------------------23
Redox reactions and titrations --------------------------------------------------------------------------------------------23
Redox and electrode potentials -------------------------------------------------------------------------------------------24
Feasibility and the extent of reactions ----------------------------------------------------------------------------------25
Applying electrochemistry--------------------------------------------------------------------------------------------------26
Transition metals -------------------------------------------------------------------------------------------------------------28
Chemistry of chromium and copper -------------------------------------------------------------------------------------28
Uses of transition metals ---------------------------------------------------------------------------------------------------30
Observations on transition metals ions ---------------------------------------------------------------------------------31
Organic chemistry- arenes, nitrogen compounds and synthesis -----------------------------------------------------33
Benzene chemistry -----------------------------------------------------------------------------------------------------------33
Amino compounds -----------------------------------------------------------------------------------------------------------36
Amides and polyamides -----------------------------------------------------------------------------------------------------37
Amino acids --------------------------------------------------------------------------------------------------------------------39
Organic synthesis -------------------------------------------------------------------------------------------------------------41
Organic synthesis techniques ----------------------------------------------------------------------------------------------43

2

Edexcel

A2 Chemistry

Revision Notes

UNIT 4
How fast? – Rates
Rate of reaction
π‘…π‘Žπ‘‘π‘’ π‘œπ‘“ π‘Ÿπ‘’π‘Žπ‘π‘‘π‘–π‘œπ‘› =

π‘β„Žπ‘Žπ‘›π‘”π‘’ 𝑖𝑛 π‘π‘œπ‘›π‘π‘’π‘›π‘‘π‘Ÿπ‘Žπ‘‘π‘–π‘œπ‘›
π‘‘π‘–π‘šπ‘’

Rate equations
It’s the relationship between the concentrations of reactants and to what power they are raised
...

Mass change is used when a gas is produced, such as acid carbonate reactions
...

Titrimetric analysis uses titration to measure changing concentrations of a reactant or product,
such as in the fall of acid concentration during esterification
...
The gradient of the tangent to the
concentration-time graph gives the rate at that moment
...

You can find the orders from the shape of the graph, the value of k and its units by substituting
your measurements into a rearranged rate equation where π‘˜ =






π‘Ÿπ‘Žπ‘‘π‘’

...

If the gradient of the graph changes exponentially, and half-life is constant then it is a first order
reaction
...

Half-life being the time needed for any reactant concentration to decrease by half of its initial
value
...

A catalyst increases the rate of reacting by providing an alternative route of reaction with a lower
activation energy that remains chemically unchanged by the reaction
...


PROCESS
HABER SYNTHESIS
CATALYTIC
CONVERTER ON A CAR
CONTACT PROCESS,
SULPHURIC ACID
MANUFACTURE
ESTERIFICATION

REACTANTS
Nitrogen, Hydrogen
Exhaust gases

CATALYST
Iron
Platinum

TYPE OF CATALYST
Heterogeneous
Heterogeneous

Sulphur dioxide,
oxygen gases

Vanadium (V) oxide

Heterogeneous

Solutions of acid,
Hydrogen ions
Homogeneous
alcohol
Many catalysts are transition metals because they have variable oxidation states and can alter the
number of bonds available to reactants
...

Changing the temperature changes the value of k because the proportion of molecules that have the
required energy is increased and increases the number of collisions and hence the number of successful
collisions
...
31J K-1mol-1
...

𝑅𝑇

Investigating the activation energy of a reaction
Calculating the activation energy required the results from experiments at a range of different
temperatures, to give values of k at each temperature
...
This is
also an example of a clock reaction
...

The value can then be calculated by using the Arrhenius equation
...
If a
reactant is zero order in the rate equation, which means it isn’t involved in the rate determining step
however must be involved in another faster step
...


The single step of substitution involves two species, the hydroxide ion and the primary halogenoalkanes
...
This is called an SN2
mechanism
...

Tertiary halogenoalkanes hydrolyse by an alternative SN1 mechanism
...

The slow step only involves one species, as the breaking of the bond isn’t dependent of the concentration
of hydroxide ions
...


Kinetics of the reaction between Propanone and iodine in acid solution
𝐼2 + 𝐢𝐻3 𝐢𝑂𝐢𝐻3 β†’ 𝐢𝐻2 𝐼𝐢𝑂𝐢𝐻3 + 𝐻𝐼
Hydrogen ions catalyse the reacting
The rate equation has the form π‘Ÿπ‘Žπ‘‘π‘’ = [𝐢𝐻3 𝐢𝑂𝐢𝐻3 ] π‘₯ [𝐼2 ] 𝑦 [𝐻 + ] 𝑧
Varying the concentrations of each of the species gives the order of each
The reaction can be followed by titrating the remaining unreacted iodine with sodium thiosulfate
and starch indicator
...
Since iodine is brown-red, a blue-green filter is used
...
It can be thought as the spreading of energy between the
particles in a system or between a system and its surroundings
...
As the temperature of a material increases, the particles gain energy and their
motion increases
...

Entropy also increases with a change of state, as there is a greater freedom of movement there is an
increase in disorder hence increase in entropy
...

A reaction that releases a gas causes an increase in entropy because gas particles are more disordered
that those in solution
...

The greater the disorder the more likely for the process to occur
...


Calculating changes in entropy, βˆ†S
Entropy values depend on physical state and temperature
...
e
...

Standard entropy, SβŠ–, is the entropy of a substance at standard temperature and pressure, expressed per
mole of substance
...

βŠ–
βŠ–
βˆ†π‘† βŠ–
π‘ π‘¦π‘ π‘‘π‘’π‘š = βˆ‘ 𝑆 π‘π‘Ÿπ‘œπ‘‘π‘’π‘π‘‘π‘  βˆ’ βˆ‘ 𝑆 π‘Ÿπ‘’π‘Žπ‘π‘‘π‘Žπ‘›π‘‘π‘ 

Spontaneous reaction, enthalpy and entropy
Spontaneous processes are often exothermic, the give out heat resulting in a negative βˆ†H, which
increases the disorder of the surrounding particles
...

Whether a reaction occurs spontaneously cant alone be determined by enthalpy changes, it’s the total
entropy change that determines if a reaction is spontaneous or not:
βˆ†π‘† π‘‘π‘œπ‘‘π‘Žπ‘™ = βˆ†π‘† π‘ π‘¦π‘ π‘‘π‘’π‘š + βˆ†π‘† π‘ π‘’π‘Ÿπ‘Ÿπ‘œπ‘’π‘›π‘‘π‘–π‘›π‘”π‘ 
For the reaction to be spontaneous βˆ†π‘† π‘‘π‘œπ‘‘π‘Žπ‘™ > 0
...

The value of βˆ†π‘† π‘ π‘’π‘Ÿπ‘Ÿπ‘œπ‘’π‘›π‘‘π‘–π‘›π‘”π‘  depends on the temperature and energy transferred:
βˆ’βˆ†π»
βˆ†π‘† π‘ π‘’π‘Ÿπ‘Ÿπ‘œπ‘’π‘›π‘‘π‘–π‘›π‘”π‘  =
𝑇

6

Edexcel

A2 Chemistry

Revision Notes

Feasibility of reactions
CHANGE

EXO/
βˆ†π‘Ί π’”π’–π’“π’“π’π’–π’π’…π’Šπ’π’ˆπ’”
ENDOTHERMIC

DISSOLVING SODIUM
NITRATE IN WATER

Endothermic

Decreases

SODIUM METAL
BURNING IN CHLORINE

Exothermic

Increases

AMMONIA GAS AND
HYDROGEN CHLORIDE
GAS COMBINE TO GIVE
SOLID AMMONIUM
CHLORIDE

Exothermic

Increases

βˆ†π‘Ί π’”π’šπ’”π’•π’†π’Ž

Increases
because the
crystalline
lattice is
destroyed
Decreases
because
crystalline
lattice is
formed
Decreases
because a
lattice forms

βˆ†π‘Ί 𝒕𝒐𝒕𝒂𝒍

+ve

+ve

+ve

WHY IS THE
CHANGE
SPONTANEOUS?
βˆ†π‘† π‘ π‘¦π‘ π‘‘π‘’π‘š is
larger

βˆ†π‘† π‘ π‘’π‘Ÿπ‘Ÿπ‘œπ‘’π‘›π‘‘π‘–π‘›π‘”π‘ 

βˆ†π‘† π‘ π‘’π‘Ÿπ‘Ÿπ‘œπ‘’π‘›π‘‘π‘–π‘›π‘”π‘ 
is larger

Feasibility, stability and inertness
The key factors for the feasibility of a reaction are:





The entropy change in the system
The temperature measured in kelvin
...
An example is
methane and oxygen, which don’t ignite spontaneously at room temperature
...
The thermodynamic stability of a
compound relative to its elements depend on the enthalpy level of the products relative to the reactants
...
A negative enthalpy of formation indicates that a
compound is more stable that its elements- it must form exothermically from its elements
...
A high activation energy barrier may prevent a
reaction starting, in such cases the reactants are said to kinetically stable or kinetically inert
...




Lattice energy – the solid lattice must separate into individual ions, which is an endothermic
process
 Hydration enthalpy – separate ions must interact with polar solvent, such as water which is an
exothermic change
Hence enthalpy of solution is: βˆ†π» π‘ π‘œπ‘™π‘’π‘‘π‘–π‘œπ‘› = βˆ’ βˆ†π» π‘™π‘Žπ‘‘π‘‘π‘–π‘ π‘’π‘›π‘’π‘Ÿπ‘”π‘¦ + βˆ†π»β„Žπ‘¦π‘‘π‘Ÿπ‘Žπ‘‘π‘–π‘œπ‘›
When a new lattice forms from gaseous ions it is an exothermic process, which is the lattice energy
...






A positive βˆ†π» π‘ π‘œπ‘™π‘’π‘‘π‘–π‘œπ‘› means an overall endothermic process, which is where dissolving isn’t
favoured
...

o For example sodium chloride has a low entropy value
...
The products have less energy than the reactants in general
...

It isn’t possible to directly calculate enthalpy of hydration so instead we use a Hess’ cycle
...

These interactions are exothermic and the system shows a decrease in enthalpy
...


8

Edexcel

A2 Chemistry

Revision Notes

Equilibria
Equilibrium mixtures
Dynamic equilibrium is where the rate of the forwards reaction is equal to that of the backwards, and
concentrations of reactants and products remain constant, which can only be obtained in a closed
system
...

π‘Žπ΄ + 𝑏𝐡 β†’ 𝑐𝐢 + 𝑑𝐷
[𝐢] 𝑐 [𝐷] 𝑑
𝐾𝐢 =
[𝐴] π‘Ž [𝐡] 𝑏

Homogeneous and heterogeneous systems
Homogenous are where all reactants and products are in the same state, however in a heterogeneous
system where the states are different, any solid concentrations can be ignored and considered as
constant in the reaction
...


KP in homogeneous and heterogeneous systems
In a heterogeneous system the solid is once again taken as constant, if liquid also is present then
concentration must be used
...

It uses the partial pressures of each component of the reaction, where partial pressure is the pressure
that would be exerted if the amount of that gas filed he whole container alone
...
Changing the pressure has no
effect on its value, although it may affect the position of equilibrium and hence yield of product
Their value only changes with temperature, which may also the position of equilibrium

More on equilibrium constants
Calculating KC from experimental data
Alcohols react reversibly with carboxylic acids to form esters
...
The
concentration of substances can be found by titration, knowing initial amounts of alcohol and acid, the
four equilibrium concentrations can be calculated and can be sued in the KC expression
...


Equilibrium using immiscible solvents
Iodine is soluble in both hexane and in aqueous potassium iodide solution
...
The iodine solute distributes itself between the two solvents
...

[π‘ π‘œπ‘™π‘’π‘‘π‘’ 𝑖𝑛 π‘ π‘œπ‘™π‘£π‘’π‘›π‘‘ 𝐴]
[π‘ π‘œπ‘™π‘’π‘‘π‘’ 𝑖𝑛 π‘ π‘œπ‘™π‘£π‘’π‘›π‘‘ 𝐡]
Large partition coefficient i
...
greater than 1, indicates that the iodine is much more soluble in the less
π‘π‘Žπ‘Ÿπ‘‘π‘–π‘‘π‘–π‘œπ‘› π‘π‘œπ‘’π‘“π‘“π‘–π‘π‘–π‘’π‘›π‘‘ =

dense solvent (the upper layer)
...


Entropy and the equilibrium constant
It’s difficult to apply the idea of entropy to equilibrium as there are two reactions going on
simultaneously
...

Total entropy would not also indicate the spontaneous direction of reaction but also the extent it
takes place
...


10

Edexcel

A2 Chemistry

Revision Notes

Using entropy to explain the effect of temperature on an equilibrium
constant
Exothermic and endothermic reactions both affect the entropy of the surroundings
...
e
...
Hence equilibrium yield, equilibrium constant
and rate constant are affected by changes in reaction conditions
...
The
temperature effects on yield can be summarized as follows:





When the enthalpy of reaction is positive, k (equilibrium constant) increases with temperature,
giving more of the product
When change is negative, k falls with temperature increase, giving more product
Increased temperature increases rate constant k, so rate increase with increasing temperature

Effect of concentration and pressure changes on equilibrium and rate





Adding more reactant to an equilibrium mixture accelerates the forward reaction
As the amounts of products increase, the reverse reaction starts to speed up
...


 Arrhenius acids give hydrogen ions H+ in aqueous solution
 Arrhenius bases give hydroxide ions OH- in aqueous solution
However this doesn’t extent to include non-aqueous solvents such as liquid ammonia
...
Some acids and bases only partly dissociate in
aqueous solution are weak acids (ethanoic acid) and weak bases (ammonia)
...

𝐾𝑀 = [𝐻 + ][π‘‚π»βˆ’ ]
The ionisation of water is endothermic, so equilibrium shifts right at higher temperatures, so Kw depends
on temperature
...


12

Edexcel

A2 Chemistry

Revision Notes

Dilution effects
In strong acids ions have fully dissociate in dilute aqueous solution, hence [𝐻 + ] = [π‘Žπ‘π‘–π‘‘]
...
However diluting a weak acid is different, since it’s an
equilibrium reaction it increases the degree of dissociation into ions

Dissociation constant for acids, Ka
Weak acids and bases only partially dissociate in aqueous solution
...

πΎπ‘Ž =

+
βˆ’
[𝐻(π‘Žπ‘ž) ][𝐢𝐻3 𝐢𝑂𝑂(π‘Žπ‘ž) ]

[𝐢𝐻3 𝐢𝑂𝑂𝐻(π‘Žπ‘ž) ]
π‘πΎπ‘Ž = βˆ’ log πΎπ‘Ž

The smaller the Ka the weaker the acid
...
Allowing us to calculate Ka from pH or vice versa
...
g
...


13

Edexcel

A2 Chemistry

Revision Notes

Indicators
Colour-change indicators are weak organic acids or base:
𝐻𝐼𝑛 ↔ 𝐻 + + πΌπ‘›βˆ’
Colour A
Colour B
A suitable indicator lays between the vertical sections on pH titration curve
...

 An acidic buffer contains a weak acid and its salt
...
g
...
E
...
ammonia and ammonium chloride
 Addition of H+ ions combine with conjugate base for the salt, to give a largely undissociated acid
...


Calculating the pH of a buffer solution
πΎπ‘Ž =

+
[𝐻(π‘Žπ‘ž) ][π΄βˆ’ ]
(π‘Žπ‘ž)

+
[𝐻(π‘Žπ‘ž) ] =

[𝐻𝐴(π‘Žπ‘ž) ]
πΎπ‘Ž Γ— [𝐻𝐴(π‘Žπ‘ž) ]
[π΄βˆ’ ]
(π‘Žπ‘ž)

Because HA only partially dissociates, HA at equilibrium is virtually equivalent to HA concentration initially
...
A chiral centre of a molecules
gives way to optical isomerism, which means the molecule is able to rotate a plane of plane polarised
light
...
An optical isomer rotates light to the right and the other rotates light
to the left by the same magnitude
...

An equimolar mixture of the two enantiomers is called a racemic mixture which is optically inactive
...


Aldehydes and ketones
Aldehydes and ketones both contain the same functional group, a carbonyl compound, C=O
...
Aldehydes carbonyl group is
bonded to a hydrogen, whereas in ketones it is bonded to a second hydrocarbon group, which can also
be an aryl group (like a benzene ring)
...
The carbonyl
bond doesn’t exhibit hydrogen bonding unless in aqueous solution, unlike the –OH group of alcohols
...
The forces of attraction between
molecules increases in the molecules can stack closely, hence straight chain molecules have higher
boiling points
...


Solubility in water
The polar bond of the carbonyl group allows hydrogen bonding to occur in polar solvents such as water
for short-chain compounds
...


Reactions of carbonyl compounds
The main difference between aldehydes and ketones is that aldehydes are easily oxidised to carboxylic
acids but ketones resist further oxidation
...


OXIDISING AGENT
FEHLING’S OR BENEDICT’S
SOLUTION
TOLLEN’S REAGENT (SILVER
MIRROR REACTION)
ACIDIFIED DICHROMATE (V1)
SOLUTION

ALDEHYDE
From blue to red-brown
precipitate
Reduction of Cu(11) to Cu(1)
Colourless to silver mirror or
silver precipitate
Reduction of Ag (1) to Ag
Orange to green
Reduction of Cr(V1) to Cr(111)

KETONE
No effect

No effect

No effect

15

Edexcel

A2 Chemistry

Revision Notes

Reduction of aldehydes and ketones
 Reduction of aldehydes give primary alcohols
 Reduction of ketones give secondary alcohols
The reducing agent used for these reactions is LiAlH4, lithium tetrahydridoaluminate
...

Nucleophiles will attack the carbon atom
...
Use of the alkali metal cyanide instead, KCN, gives enough concentration of the

nucleophile for nucleophilic addition
...
The product however displays no optical activity hence must
occur from above as below
...
2, 4dinitrophenylhydrazine (2, 4-DNP or Brady’s reagent) adds to a carbonyl group with the elimination of
water
...


The derivatives produced from the reaction can be used to identify specific aldehydes and ketones
...
Each derivative has a
specific melting point
...


16

Edexcel

A2 Chemistry

Revision Notes

Iodoform test (triiodomethane)
Organic compounds with a methyl group bonded adjacent to a carbonyl group gives a positive result to
an Iodoform reaction
...
A positive result is the production of a
yellow precipitate or triiodomethane with a characteristic antiseptic smell
...
The presence of the –OH group gives way to two different physical properties
...


Preparation of acids
Carboxylic acids can be prepared by the oxidation of primary alcohols, using acidified potassium

dichromate (V1) or potassium manganate (V11)
...


Reactions of carboxylic acids


Complete reduction gives primary alcohols, a strong reducing agent is needed for example lithium
tetrahydridoaluminate




The neutralisation of carboxylic acids gives carboxylate salts:
Reaction of acids with phosphorus (V) chloride is called halogenation and gives an acyl chloride
...

Esterification occurs when carboxylic acids react with an alcohol:
π΄π‘™π‘π‘œβ„Žπ‘œπ‘™ + πΆπ‘Žπ‘Ÿπ‘π‘œπ‘₯𝑦𝑙𝑖𝑐 π‘Žπ‘π‘–π‘‘ β†’ Ester + Water
The reaction is reversible and requires a hydrogen catalyst, because the reaction is reversible it
doesn’t go to completion often resulting in a poor yield of ester
...






A carboxylic can be identified by reacting with a metal carbonate which produces effervescence
and turns lime water cloudy

17

Edexcel

A2 Chemistry

Revision Notes

Esters and polyesters
Esters are derivatives of carboxylic acids
...

They are volatile compounds
...
A typical characteristic of an
ester is they have a pleasant smell
...


Naming esters
1
...

3
...


Identify acid – e
...
butanoic acid
Change the –oic ending to the salt name –oate
Identify group from the alcohol- e
...
the methyl from methanol
Combine by alkyl group followed by salt -e
...
methyl butanoate

Reactions of esters
1 The reverse reaction of esterification, hydrolysis of an ester:
ester + water ↔ π‘Žπ‘™π‘π‘œβ„Žπ‘œπ‘™ + π‘π‘Žπ‘Ÿπ‘π‘œπ‘₯𝑦𝑙𝑖𝑐 π‘Žπ‘π‘–π‘‘
Hydrolysis can be catalysed by adding dilute hydrochloric acid, or sulphuric acid and boiling under reflux
...
The initial carboxylic acid product reacts with the base (sodium
hydroxide) to give the sodium salt
...
Soap making is called saponification
...
It involves converting one ester into another
...
A base catalyst is used:
π‘‘π‘Ÿπ‘–π‘”π‘™π‘¦π‘π‘’π‘Ÿπ‘–π‘‘π‘’ + π‘Žπ‘™π‘π‘œβ„Žπ‘œπ‘™ ↔ π‘π‘–π‘œπ‘‘π‘–π‘’π‘ π‘’π‘™ + π‘”π‘™π‘¦π‘π‘’π‘Ÿπ‘œπ‘™
Biodiesel is alternative to fossil fuels and is renewable, but requires agricultural land
...
They can be
made by combining a single monomer unit or two types of monomer units
...


Acyl chlorides
They are derivatives of carboxylic acids
...

𝐢𝐻3 𝐢𝑂𝑂𝐻(𝑙) + 𝑃𝐢𝑙5(𝑠) β†’ 𝐢𝐻3 𝐢𝑂𝐢𝑙(𝑙) + 𝐻𝐢𝑙(𝑔) + 𝑃𝑂𝐢𝑙3
Naming – oic replaced by –oyl with chloride instead of acid
...
This is associated with the electron deficient carbon
atom as it is joined to two highly electronegative atoms, oxygen and chlorine
...


19

Edexcel

A2 Chemistry

Revision Notes

Reactions of acyl chlorides
1 reaction with water
Acyl chlorides undergo nucleophillic attack more rapidly than halogenoalkanes, and react vigorously with
water at room temperature
...
The disadvantage present in esterification is
that it is reversible and doesn’t go to completion
...


3 Reaction with concentrated ammonia
Acyl chlorides react vigorously and sometimes violently with conc
...
The reaction gives acid
amides as products, general formula RCONH2
...
The acyl group replaces on of
the hydrogens of the amine group
...


20

Edexcel

A2 Chemistry

Revision Notes

Spectroscopy and chromatography
Spectroscopy
Infrared radiation analysis of the progress of a reaction
Infrared spectroscopy, is where IR is absorbed by molecules and each functional group absorbs different
vibrational frequencies, producing a characteristic peak in the IR spectrum
...
As long as the alterations of groups is distinct enough
...
These splitting patterns, called spin-spin coupling patterns, are due to the spin states of
protons on adjacent carbon atom
...


MRI scanners
Medical diagnosis can be made from MRI (magnetic resonance imaging)
...
The H nuclei in water in the body interact with
radio waves
...


21

Edexcel

A2 Chemistry

Revision Notes

UV, mass spectra and chromatography
When some materials absorb UV they undergo homolytic fission, producing free radicals, such as
chlorine, which have an unpaired electron and can go on to initiate free radical substitution chain
reaction
...
It is used in industrial processes to monitor the presence and absence of materials at different
stages of a process
...
The time taken to travel through the column is the retention time
...


High performance liquid chromatography (HPLC)
HPLC improves the separation of components in a mixture, allowing more effective analysis
...

Separate components can be washed off the column using a solvent
...


22

Edexcel

A2 Chemistry

Revision Notes

UNIT 5
Redox and the chemistry of the transition metals
Redox reactions and titrations
Redox is electron transfer between species, remember OILRIG; Oxidation Is Loss and Reduction Is Gain of
electrons
...
e
...
e
...
The oxidation of a species increase, tis been
oxidised and reduced when value decreases
...


Half equations
Ionic half equations show a loss or gain in electrons, and combine the two half equations gives a full and
balanced overall equation
...









Potassium manganate (VII) is a powerful oxidising agent and has an intense purple colour
In acidic solution it’s reduced to an almost colourless manganese (II) salt
The potassium manganate (VII) of known conc
...

The titration is self-indicating
The end point is when all the iron (ii) has been oxidised, which gives a permanent pink colour
Calculation can be made using the known molar ratio, as well as volume of solution of iron (II)

Redox titrations 2
Another redox titration is using sodium thiosulfate, with aqueous iodine:






Iodine is solution is a brown colour
Adding thiosulfate results is an light brown/ yellow colour as iodine is reduced giving colourless
solution as end point
Near the end point solution is still pale yellow, so starch indicator is added so the end point is from
blue to colourless, which shows iodine has all reacted
This titration can be used to fin concentration of an oxidising agent that oxidises iodide ions to
iodine such as copper (II) ions

23

Edexcel

A2 Chemistry

Revision Notes

Measurement uncertainty and implications
Uncertainty can be caused by poor technique or limited precision of the apparatus
...
g
...
From a simple cell, two half cells must be joined
together without the introduction of another metal, so a
salt ridge completes the circuit
...
m
...

The standard electrode potential is the e
...
f value between
the two half cells used, measured under standard
conditions
...


Standard cells and standard electrode potentials
Electrode potentials are relative to each other
...
The standard hydrogen half-cell has a defined
e
...
f of zero volts under standard conditions
...


Cell conventions
The short hand convention for notating a half-cell is:




The metal electrodes are written at the ends with a line separating then from their aqueous ions
The slat bridge is a double vertical dotted line representing the salt bridge

24

Edexcel

A2 Chemistry

Electrolyte in contact with left
hand electrode
Left hand electrode

Revision Notes

Electrolyte in contact with
right hand electrode

2+
2+
𝑍𝑛(𝑠) 𝑍𝑛(π‘Žπ‘ž ) ¦¦𝐢𝑒(π‘Žπ‘ž ) 𝐢𝑒(𝑠)

Right hand electrode

This is the cell e
...
f which is RHS - LHS

𝐸 = +1
...
e
...


Calculating cell potentials, Ecell
The left hand electrode is the most negative potential
...
The negative value wouldn’t occur, so would imply the reverse direction would in fact be the
forwards direction
...
A feasible reaction could be extremely slow and of little use
...
Due to the lack of standard conditions fir most reactions limits
the use of standard electrode potentials in predicting feasibility
...
For example the activation energy may be too high
...
the value of K indicates the extent
of the reaction:
- βˆ†π‘† π‘‘π‘œπ‘‘π‘Žπ‘™ = R ln 𝐾 R-molar gas constant
Hence also proportional to lnK

Changes of oxidation state and the electrode potential
In a similar way we can use the electrode potential values to predict whether redox reaction will occur
...

Remember when selecting the potential values that transition metals have variable oxidation states
...
They turn
chemical energy of hydrogen or hydrogen rich fuels, such as alcohols into electricity
...
83𝑉
𝑐𝑒𝑙𝑙
Oxygen is supplied to the positive electrode:



1
2




βˆ’
𝑂2(𝑔) + 𝐻2 𝑂(𝑙) + 2𝑒 βˆ’ β†’ 2𝑂𝐻(π‘Žπ‘ž) 𝐸 βŠ– = +0
...
83𝑉 βˆ’ 0
...
43𝑉
𝑐𝑒𝑙𝑙

Sources of fuels for use in fuel cells




Hydrogen can be obtained from water or brine by electrolysis
Natural gas such as methane can also be a source of hydrogen (hydrogen source for the Haber
process)
Alcohols can be obtained by fermentation of sugars or by hydration of alkenes from crude oil

Advantages and limitations of fuel cells







Fuel cells are very efficient in comparison to petrol engines
Fuel cells produce no carbon dioxide emissions or pollutants such as CO at the point of usealthough the production of hydrogen may result in pollution and emissions
Hydrogen fuel cells are produced by electrolysis using electricity generated in power plants that
use fossil fuels or derived from non-renewable fossil fuels
Manufacturing hydrogen from methane, carbon is converted to carbon dioxide
They have a limited lifetime and replacement is very expensive
Hydrogen is in a gaseous state and hence is difficult to store and transport and to do s must be in
ultra-low temperatures or high pressure storage systems or by solid state absorption

Breathalyser technology
In early breathalysers the ethanol on the drivers breath was detected by a colour change in the reduction
of dichromate (VI) ions the chromium (III)
...
The amount of ethanol in the
breath depends on the concentration of alcohol in the blood, and hence β€˜mouth alcohol’ can give error in
readings
...
The OH group in ethanol is not used for IR because the presence of water in breath effects the
reading
...


27

Edexcel

A2 Chemistry

Revision Notes

Transition metals
A transition metal form one or more stable ions with a partially filled d subshell
...

Chromium and copper have unexpected electronic configuration with only one electron in the 4s
subshell, as it leaves a half filled s subshell and half-filled d subshell which is more stable than 3d4 4s2
arrangement
...


Ionisation energies
Successive ionisation energies of d-block elements give evidence for their electronic configuration
...


Ligands and complex ions
A complex transition metal has a metal ion at the centre with a number of other molecules or ions
surrounding it
...

Monodentate ligands join to the metal ion I one place and a bidentate ligand has two electron pairs to
donate
...

The overall charge on a complex ion is the sum of the charges on the metal and the ligands
...


Shapes of complex ions
They from shapes dependent on the coordination number, i
...
with coordination number 6 it forms an
octahedral complex
...

Many ligands have their own internal covalent bonds as well
...
Colour at this
frequency is removed from the white light and the complementary colour will show: i
...
when red light is
absorbed a solution will appear blue
...
The addition of ligands to the ion
splits the five orbitals into two groups of different energy
...
Similar electron transitions are not possible for either d0 or d10 ions, as there is no free
orbitals for the electron to transition to and from colourless compounds and aqueous solutions
...


Ligand exchange reactions
Some ligands bond more effective than others to the metal ion, which results in a more stable complex
...
For example:
Copper (I) chloride is prepared by boiling copper (II) chloride with conc
...
Initially tetrachlorocuprate
(II) complex ion is formed:
βˆ’
[𝐢𝑒(𝐻2 𝑂)6 ]2+ + 4𝐢𝑙(π‘Žπ‘ž) β†’ [𝐢𝑒𝐢𝑙4 ]2βˆ’ + 6𝐻2 𝑂(𝑙)
(π‘Žπ‘ž)
(π‘Žπ‘ž)

Blue




green

The charge of the complex is the total charge of the complex i
...
takes into account the charge of
the transition metal ion as well as the ligands
Neutral ligands such as water and ammonia have no effect on the overall charge of the complex
ion

In this reaction four of the water molecules are replaced with four ammonia ligands:
[𝐢𝑒(𝐻2 𝑂)6 ]2+ + 4𝑁𝐻3(π‘Žπ‘ž) β†’ [𝐢𝑒(𝑁𝐻3 )4 (𝐻2 𝑂)2 ]2+ + 4𝐻2 𝑂(𝑙)
(π‘Žπ‘ž)
(π‘Žπ‘ž)
Pale blue

deep blue

Ligand exchange and stability of complex ions



Monodentate ligands such as ammonia and water have a single lone pair that they use to form
a dative covalent bond tot eh metal ion
Polydentate ligands such as EDTA, have several lone pairs available
...
Such as
when Monodentate ligands are replaced by a polydentate ligand then the total moles increases, this
results in a positive entropy change
...
Electrode potential values can be used to
predict whether copper (I) ion will disproportionate, the half equations are:
2+
+
𝐢𝑒(π‘Žπ‘ž) + 2𝑒 βˆ’ β†’ 𝐢𝑒(π‘Žπ‘ž)

𝐸 βŠ– = +0
...
52𝑉

The reaction with the more positive value will go forward, and hence the other will go backwards
...

+
2+
2𝐢𝑒(π‘Žπ‘ž) β†’ 𝐢𝑒(𝑠) + 𝐢𝑒(π‘Žπ‘ž)

`

𝐸 ⊝ = +0
...
15 = +0
...


29

Edexcel

A2 Chemistry

Revision Notes

Uses of transition metals
They make good catalyst due to their variable oxidation states
...
When the reaction has taken place the product diffuses away leaving the
catalyst surface available for further reaction
...
They can be poisoned by the reactant when material irreversibly binds to the
surface of the catalyst, preventing any other reaction
...
An example
is the contact process for the manufacture of sulphur trioxide, from sulphuric acid, the vanadium (V)
oxide catalyst is first reduced from +5 to +4:
𝑆𝑂2(𝑔) + 𝑉2 𝑂5(𝑠) β†’ 𝑆𝑂3(𝑔) + 𝑉2 𝑂4(𝑠)
This alternative mechanism provides a lower activation energy for the reaction to occur at
...


Catalytic converters
They use a fine coating of platinum catalyst supported on a heat resisting honeycomb ceramic material
to give a larger surface area
...
A disadvantage is that it reduces fuel economy,
catalyst can be poisoned and may take time to warm up to working temperature, releasing pollutants
...

Biological catalysts are effective at low temperatures
...
These new supramolecular
transition metal catalysts make very specific catalysis possible at low temperatures and be recovered and
reused
...

Developments are in progress for a newer version with far fewer side effects
...

It’s only effective when combined with other drugs as it enhances their effects
...

Photochromic lenses, are where the glass goes darker in sunlight and paler when light becomes more
diffused
...
The molecules change shape according to the UV
intensity, in artificial light they remain transparent
...


Observations on transition metals ions
A few metals such as zinc and chromium form precipitates that dissolve in excess sodium hydroxide
giving a solvent again
...
The metal hydroxide reacts with both acids
and bases
...
Zinc forms a white
precipitate on a small amount of sodium hydroxide and ammonia and colourless solution upon excess
...


31

Edexcel

A2 Chemistry

π‘ͺ𝒓 πŸ‘+
VIOLET

𝑴𝒏 𝟐+
VERY PALE PINK

COLOUR IN
AQUEOUS
SOLUTION
REACTION WITH SODIUM HYDROXIDE SOLUTION
REACTION
BLUE-VIOLET
GELATINOUS
WITH SMALL Chromium (III)
WHITE
AMOUNT OF hydroxide
Manganese(II)
πΆπ‘Ÿ(𝐻2 𝑂)3 (𝑂𝐻)3
SODIUM
hydroxide,
HYDROXIDE
𝑀𝑛(𝑂𝐻)2 , turns
SOLUTION
brown on
standing in air
REACTION
Precipitate
INSOLUBLE
WITH
dissolves to
EXCESS
from green
SODIUM
solution
HYDROXIDE
containing,
[πΆπ‘Ÿ(𝐻2 𝑂)2 (𝑂𝐻)4 ]βˆ’
SOLUTION
REACTION WITH AQUEOUS AMMONIA SOLUTION
REACTION
BLUE-VIOLET
GELATINOUS
WITH SMALL Chromium (III)
WHITE
AMOUNTS
hydroxide
Manganese(II)
πΆπ‘Ÿ(𝐻2 𝑂)3 (𝑂𝐻)3
OF
hydroxide,
AQUEOUS
𝑀𝑛(𝑂𝐻)2 , turns
AMMONIA
brown on
standing in air
REACTION
Precipitate
INSOLUBLE
WITH
dissolves to
EXCESS
form YELLOW
AQUEOUS
solution,
[πΆπ‘Ÿ(𝑁𝐻3 )6 ]3+
AMMONIA

Revision Notes

𝑭𝒆 𝟐+
PALE BLUEGREEN

𝑭𝒆 πŸ‘+
YELLOW

π‘΅π’Š 𝟐+
EMERALD
GREEN

π‘ͺ𝒖 𝟐+

GELATINOUS
PALE GREEN
Iron(II)
hydroxide,
𝐹𝑒(𝑂𝐻)2 , turns
brown on
standing in air
INSOLUBLE

REDDISHBROWN
Iron(III)
hydroxide,
𝐹𝑒2 𝑂3 βˆ™ π‘₯𝐻2 𝑂
Also written,

EMERALD
GREEN
Nickel(II)
hydroxide,
𝑁𝑖(𝑂𝐻)2

GELATINOUS BLUE
copper (II)
hydroxide,
𝐢𝑒(𝑂𝐻)2

INSOLUBLE

INSOLUBLE

INSOLUBLE

GELATINOUS
PALE GREEN
Iron(II)
hydroxide,
𝐹𝑒(𝑂𝐻)2 , turns
brown on
standing in air
INSOLUBLE

REDDISHBROWN
Iron(III)
hydroxide,
𝐹𝑒2 𝑂3 βˆ™ π‘₯𝐻2 𝑂
Also written,

EMERALD
GREEN
Nickel(II)
hydroxide,

GELATINOUS BLUE
copper (II)
hydroxide,
𝐢𝑒(𝑂𝐻)2

BLUE

𝐹𝑒(𝐻2 𝑂)3 (𝑂𝐻)3

𝑁𝑖( 𝑂𝐻)2

𝐹𝑒(𝐻2 𝑂)3 (𝑂𝐻)3

INSOLUBLE

Precipitate
dissolves to
from
LAVENDER
BLUE solution,
[𝑁𝑖(𝑁𝐻3 )6

Precipitate
dissolves to form
DEEP BLUE
solution,
[𝐢𝑒(𝑁𝐻3 )4 (𝐻2 𝑂)2 ]2+

]2+

32

Edexcel

A2 Chemistry

Revision Notes

Organic chemistry- arenes, nitrogen compounds and
synthesis
Benzene chemistry
The benzene structure is an aromatic compound- a ring structure
...

This isn’t the best representation of benzene for several reasons
The more accurate representation of benzene is the one that shows a delocalised pi system, a ring
within the hexagon
...


The reason the second representation is more accurate is supported by X-ray analysis that shows equal
bond lengths whereas the double bonds are shorter than the single, hence would support the Kekule
structure
...

The delocalised ring gives benzene its stability because more energy is needed to break down the bonds
compared to having separate pi bonds as used in the Kekule structure
...
The high
carbon:hydrogen ratio in benzene results in a smoky yellow flame
...
Substitution preserves the stable delocalised
ring structure and are the favoured reactions
...


The mechanism involves the electrophile Br+
...
The electrophile is made using a halogen carrier, such as iron (III) bromide:
βˆ’
πΉπ‘’π΅π‘Ÿ3 + π»π΅π‘Ÿ β†’ 𝐻 + + πΉπ‘’π΅π‘Ÿ4
The iron (III) bromide is reformed and hence acts as a catalyst
...
The electrophile is
the nitronium ion, NO2+ formed from a mixture of conc
...


Above 50℃ gives rise to multiple substitutions:

Sulfonation
This reaction is carried out with fuming sulphuric acid (conc
...
This very string acid reacts under reflux with benzene to give benzenesulfonic acid, the
electrophile being sulphur trioxide
...


Friedel-crafts reactions
These introduce a side chain into the benzene ring
...

+
βˆ’
The electrophile is generated: 𝐢𝐻3 𝐢𝐻2 𝐢𝑙 + 𝐴𝑙𝐢𝑙3 β†’ 𝐢𝐻3 𝐢𝐻2 + 𝐴𝑙𝐢𝑙4
...


The presence of a methyl side chain activates the ring towards substitution reactions
...


Phenol
In phenol there is an OH group, which too activate the ring towards substitution
...

The reaction gives multiple substitutions at several points on the ring, showing the ring has been
activated
...


35

Edexcel

A2 Chemistry

Revision Notes

Amino compounds
Ammonia has a lone pair of electrons on the nitrogen atom
...
Amines are an important derivative ammonia with the functional group NH2
...
They are named
in standard convention i
...
butylamine C4H9NH2, an aliphatic amine and phenylamine, C6H5NH2 is an
aromatic amine, containing a benzene ring
...

+
βˆ’
𝐢2 𝐻5 𝑁𝐻2(π‘Žπ‘ž) + 𝐻2 𝑂(𝑙) β‡Œ 𝐢2 𝐻5 𝑁𝐻3(π‘Žπ‘ž) + 𝑂𝐻(π‘Žπ‘ž)

ethylammonium ion

Preparation of amines
Aromatic amines are prepared by reduction of aromatic nitro compounds, such as nitrobenzene, by reflux
of tin and concentrated hydrochloric acid
...


Properties of amines











Like ammonia, amines have unpleasant smalls
Like ammonia, aqueous solutions of amines are alkaline
The hydrocarbon part of the molecules (residue) is hydrophobic but the amine group is able to
hydrogen bond with itself and water
...
Hence the greater the
hydrocarbon chain the lower its solubility of an amine in water
...
Amines
can act as nucleophiles in the reaction with halogenoalkanes- the lone par is attracted towards
the 𝛿 + carbon in the halogenoalkane
...


36

Edexcel

A2 Chemistry

Revision Notes

Diazotization and synthesis of dyes
Aromatic amines can be converted into Diazonium slats by reaction with nitrous acid, HNO2
...
At this lower temperature Diazonium compounds can be used to produce a range of useful
products such as dyes
...
Reactions between
diazonium compounds and aromatic amine or phenol are coupling reactions
...
These dye can absorb light in the visible part of the
spectrum and appear coloured
...
Amides are carboxylic acid derivatives- and named accordingly
...
Ammonia solution
...
These reactions can also
be called condensation reactions
...
Polyamides are made by condensation polymerisation from amide monomers- the amide
bond CO-NH joins the monomer unit together
...
Polyamides such as Kevlar and
nylon can be made into strong fibres and used in clothing
...

It resists high temperatures, low thermal conductivity, high tensile strength, and flame-, chemical- and
cut- resistant
...


Addition polymerisation
This is where there are no additional products to the polymer
...


Water solubility
It’s unusual for synthetic polymers to be water soluble
...
These bags dissolve fully
in the water and bedding and clothes (in a hospital for example) are washed and clean
...


38

Edexcel

A2 Chemistry

Revision Notes

Amino acids
Amino acids contain both carboxyl and amine groups
...
These two contrasting
functional groups give amino acids unusual properties
...
Where R
is hydrogen (simplest R group), it’s called glycine
...


Acid-base properties
Amino acids have amphoteric character, as they can react with both acids and bases
...
This contains positive and a negative end,
so the molecule has no overall charge
...

The pH of the solution determines which of the two ions on the zwitterion react with protons in the
solution
...


Identifying amino acids
Mixtures of amino acids can be separated and identified using chromatography
...
This technique obviously has its limitation, especially when large number of
amino acid need to be separated
...
The amino acids move through
the gel depending on the functional group
...
Amino acids will then show up as purple spots
...


Chiral molecules rotate the plane of polarisation of monochromic plane-polarised light
...


Importance of amino acids
Amino acids can be polymerised by condensation to give peptides
...
A peptide link is formed when
COOH group of one amino acid reacts with the amine group of another
...

In proteins these chains of polypeptides form 3D arrangements, by both helixes and folded sheets held
together by hydrogen bonds between amino acids
...


40

Edexcel

A2 Chemistry

Revision Notes

Organic synthesis
It is a way of modifying existing molecules or assembling new ones, to give useful products- for example
paracetamol, dyes and polymers
...


Summary of synthetic transformations for aliphatic carbon compounds

Summary of synthetic transformations for aromatic carbon compounds
41

Edexcel

A2 Chemistry

Revision Notes

Importance of analysis
At each stage of an organic synthesis, the identity of the product ca be checked using analytical
techniques such as IR or nmr spectroscopy, chromatography or mass spectrometry
...


Deductions based on analytical data
The empirical formula of an unknown compounds is found from:




Combustion analysis- a sample is burnt in excess oxygen and the products (carbon dioxide and
water) are absorbed and measured giving percentage composition of carbon and hydrogen
The percentage composition by element

Molecular and structural formula can then be deduced by combing this data with:





Chemical reactions that indicate if a particular functional group is present
Mass spectrometry data to determine the relative molecular mass- fragmentation pattern can
indicate possible structures
IR and/ or nmr spectroscopy

The provisional identification of the hydrocarbon can be confirmed by other data from reference books,
provided the analysis is sufficiently sensitive:





Any double or triple bond in the carbon would show as a signal in IR spectrum
nmr spectrum would support the number of hydrogen environments present and the expected
splitting and relative heights and shifts
The fragmentation pattern in a mass spectrum

With larger molecules, sensitive analysis can distinguish between structural isomers
...


Drug research and discovery
A pharmaceutical industry may need to synthesise and test millions of compounds before location a few
hundred potentially useful ones
...
Using specific synthesis route, a set of
starting materials is automatically combined in slightly different ways
...
The polymer is inert but has a
suitable functional group attached to it
...
Excess reagent and their by-products wash away,
leaving the product immobilised on the beads
...


42

Edexcel

A2 Chemistry

Revision Notes

Chiral synthesis
Many drug compounds are chiral but only one of the isomers may have beneficial medical uses
...

To avoid producing the unwanted enantiomer, chiral synthesis is used to make stereospecific drugs with
a single optical isomer
...
Knowing the mechanism of the reaction can help to
plan a synthesis to produce a single optical isomer
...


Refluxing
Organic reactions usually involve the breaking of covalent bonds- a slow process often requiring
prolonged heating
...


Washing
Unwanted impurities can often be removed by shaking the reaction products with water or sodium
carbonate solution
...
When
effervescence ceases, the acid has been removed
...
When two solvents are immiscible,
the products can be concentrated in one layer and the remaining reactants in the other- the layers are
then separated using a separating funnel
...
Solubility increases with temperature
...


Drying
Organic products often contain traces of water from the aqueous reagents used
...
Decanting gives the dry product
...
Types of distillation
include, simple, fractional and stem
...


43

Edexcel

A2 Chemistry

Revision Notes

Determining of boiling and melting temperatures
Pure liquids boil within a range of 1-2℃ ; pure solids melt with a range of 1℃
...


44

Edexcel

A2 Chemistry

Revision Notes

Unit 4 questions
How fast?-Rates
Reason for an order 1 reaction

As the rate doubles the concentration of X doubles
...

Evidence that supports the theory that there is more than one step in the reaction mechanism

One of the reactants aren’t present in the rate equation, hence must exist in a faster step that’s not part
of the rate determining step
...


An increase in temperature means molecules collide with greater energy so a greater proportion of
molecules collide with sufficient energy i
...
greater than the activation energy, so more of the collisions
are successful in a given amount of time
...

How would you overcome this potential error?

A significant decrease in concentration of the control reactant i
...
the acid would result in reducing the
rate of reaction, hence result would be invalid
...
This is to ensure the concentration of acid remains constant
...


Repeat the experiment at each of the temperatures
...

How would the rate be effected if ethanoic acid was used instead of hydrochloric acid?

The rate of reaction would be lower because in comparison ethanoic acid is weaker, hence a lower
concentration of hydrogen ions would be present
...


The gradient of the graph is constant, the order with respect of the reactant is 0 as rate stays constant
meaning concentration of reactant has no effect on the rate
...

Outline a method, which isn’t sampling, which would be suitable for measuring iodine concentration
...

A titre mixture was filtered and left to stand at the same temperature overnight, how would it change the
titre?

There would be no change, although the solid precipitate would have been removed the equilibrium
concentrations would have remained the same
...


As iodide reacts to form iodine it is reduced back into iodide ions by thiosulfate ions, once all the
thiosulfate has react, the colour change then occurs
...


45

Edexcel

A2 Chemistry

Revision Notes

Reaction can occur at a lower temperature, therefore less fuel is needed using uip non-renewable
resources
...


How far-Entropy
REMEMBER- sign, units and 3sf
...


The thermometer reading would decrease by a very small amount, as energy is absorbed from the
surroundings until solution becomes infinitely dilute
...

Explain, in terms of entropy changes, why sodium dissolves in water under standard conditions
...
The increase in entropy of the system is greater than the
decrease in entropy of the surroundings
...


The enthalpy change when one mole of gaseous ions dissolve in sufficient water to produce an infinitely
dilute solution
...

Explain the trend of lattice energies relative to ionic radii

As ionic radius increases the lattice energy becomes less negative, due to an increase in distance between
nuclei in the lattice
...


Lattice energy and hydration enthalpy can be used to calculate the solubility of a compound
...

By considering thermodynamic stability and kinetic inertness, explain why hydrogen doesn’t react with
oxygen unless ignited
...
However the mixture
is kinetically inter because the reaction has a very high activation energy
...

Explain why a reaction is thermodynamically spontaneous, in terms of physical states and movement of
molecules in the surroundings
...
The entropy of the surroundings is positive because the
standard enthalpy change is negative
...

Why is calcium carbonate thermodynamically stable at room temperature?

The enthalpy change for the reaction is positive
...

Calculating enthalpy of hydration, for lattice enthalpy diagram
...


Radius of the cation increases down the group (group 2) so forces of attraction between ions decreases
as charge density of ion decreases, resulting in the lattice energy to become less negative
...
Solubility
depends on relative size of lattice energy and enthalpy of hydration, the more negative enthalpy of
solution is the more likely it is to dissolve
...


The third ionisation energy of magnesium is very high, as the electron is being removed from a full 2p
subshell, so the enthalpy of formation is likely to highly endothermic
...
The volume
decrease as the water molecules pack more tightly around the ions, hence meaning the bonds between
ions and water are shorter
...


Increasing the temperature would decrease the value of the entropy of surrounding, as enthalpy change
would become less negative, and assuming that the entropy of the system remains constant, the total
entropy change would also become less positive and decrease
...


If the enthalpy change is zero then the reaction isn’t endothermic nor exothermic so changing the
temperature wont effect the equilibrium constant and hence the total entropy change will remain
constant
...


Equilibria
REMEMBER – solids aren’t included in equilibrium expression
Temperature of the equilibrium mixture is lowered
...


Equilibrium shifts left to oppose the change as the reaction is endothermic in the forwards direction
...
The yield would also
decrease as the production of more reactants is favoured
...
What would happen to the composition of the equilibrium mixture?

The position of equilibrium would be obtained quicker however would not alter the composition of the
equilibrium mixture
...
This is because there are the same number of moles on both
sides of the equation
...
Considering any change to Kc explain the effect on the equilibrium
position
...
Change in pressure
increases the value of the numerator more than the denominator, therefore quotient would be larger,
however equilibrium would shift left, which increases the value of the denominator and decreases the
numerator until the quotient is restored
...


The entropy of surroundings becomes less negative as the temperature increase which in turn increases
the total entropy and because the entropy total increases the equilibrium constant increases
...


The sodium thiosulfate reacts rapidly with iodine, which prevents the blue-black (starch-iodine) colour
before a fixed amount of the thiosulfate has reacted
...

48

Edexcel

A2 Chemistry

Revision Notes

The reaction is endothermic and 1:7 mole ratio
...
To
decrease constant, a decrease in pressure as endothermic forwards as T increase K increases
...


The ionisation of the acid is negligible hence the concentration of the acid initially and the concentration
of acid at equilibrium are equivalent
...

Why is the pH calculation of a stronger acid less accurate?

The assumption that there is negligible dissociation of the acid become invalid
...
As there is a vertical section on the PH curve
between 6-11 and the indicator lays within that range at (8
...

pH of a strong acid decrease by I unit when diluted by scale factor of ten, why does a weak acid behave
differently?

Equilibrium of the weak acid; 𝐻𝐴 + 𝐻2 𝑂 β‡Œ π΄βˆ’ + 𝐻3 𝑂+ , upon the dilution of the acid, increase water,
equilibrium shifts right resulting in a greater than expected concentration of hydrogen ions and therefore
the decrease in concentration of hydrogen ion is less than expected and change in pH isn’t as dramatic
...


The buffer contains a large reservoir of HA and A-
...
On the addition of
alkali the OH- reacts with H+ to produce water and hence shifts equilibrium right producing more acid to
dissociate and replaces the H+
...


Further organic chemistry
Explain the term chiral and what feature of the molecule makes it chiral
...
The carbon atom had four different groups
bonded to it
...

Mixture B is a racemic mixture, hence wouldn’t show any optical activity
...

What does this indicate about the first stage of the mechanism?

This means that only one enantiomer is formed, meaning it must have occurred via a SN2 mechanism
where a 5-bonded intermediate carbocation is produced
...

How can an optically active isomer produce a mixture showing no optical activity?

49

Edexcel

A2 Chemistry

Revision Notes

A racemic mixture is formed, which suggests a trigonal planar intermediate is formed, hence the
nucleophile is equally likely to attack from above or below, resulting in an equal mixture of the two
enantiomers
...
the
both products can be used in the manufacture of the product
...

Explain in term of intermolecular forces why the boiling temperature of ethanoic acid is greater than
ethanol which is greater than ethanal
...
Hydrogen bonds are
stronger than London forces
...

Give two suitable tests to distinguish between and carboxylic acid and an aldehyde
...
A test for the carboxylic acid would be adding phosphorous pentachloride
which would produce white steamy fume due to the reacting of the OH group on the carboxylic acid
...

Give advantages and disadvantages of using butanoyl chloride compared to butanoic acid, with methanol to
make methyl butanoate
...
Disadvantages: it is
more expensive and is corrosive, toxic corrosive fumes of HCl are produced and has a lower atom
economy
...


Spectroscopy and chromatography
Suggest why one of the absorption peaks in IR spectroscopy is so broad

The O-H is broad due to hydrogen bonding
Properties of molecules that absorb IR
...

What properties of a mixture determine the speed a compound moves through a chromatography column?

The solubility in the liquid, interactions between liquid and stationary phase, interactions between the
stationary and mobile phase, attraction from liquid, strength of London/ dipole-dipole forces
...


The e
...
f value would increase, because equilibrium would shift left, to oppose the change, hence the
overall reaction shifts right
...

What’s the function of the platinum electrode in for example Fe3+/Fe2+?

Catalyses the combination of Fe3+ and e- to allow electron transfer, by proving a reaction surface
...

Why does the electrode potential change?

When there are more electrons being produced then it becomes more negative and when less electrons
are being produced then becomes more positive
...
m
...
m
...

Three conditions necessary for a standard hydrogen electrode

Temperature at 298K, concentration of H+ is 1moldm-3 and at atm pressure of hydrogen gas
...
e
...

Disadvantages of using hydrogen-oxygen fuel cell compared to rechargeable battery for electrical energy for
a vehicle
...
Problems in transportation
...
It’s very costly
...
There is a lack of
availability of fuel
...
Fuel cells have to be replaced
regularly, they have a shorter life span
...


Electrolyte allows movement of ions between electrodes
...


Fuel cell is more efficient and produces the electricity directly
...


High cost
...

Advantages of using ethanol rather than hydrogen as a fuel cell
...
Less
explosive and flammable
...

Advantages of fuel cells over fossil fuels
...

Why can’t the e cell value alone predict if a reaction will occur?

Reaction may have a high activation energy
...

Explain how a catalyst speeds up a reaction
...
It’s faster as the process
lowers the activation energy by providing an alternative route
...

Reactants may be positioned in more favourable orientations
...
It increase likelihood of reactants coming into contact, as there are more
molecules in a given area
...


There is OH bond in water, which is likely to be on breath without alcohol being consumed
...


Additional is more reliable, as police would use fuel cell as it is more portable to determine whether to
check or not with IR at the station
...


You can check to see if you are below the legal limit to drive and hence safe to drive however it may not
be sensitive enough to give an accurate reading or encourages people to drink and drive
...


The same species is both reduced and oxidised simultaneously
...


Instead of the 4s subshell being filled before the 3d, there is a half-filled 4s subshell and half-filled 3d
orbital for chromium and full 3d subshell for copper
...

Explain why Cu+ ions are colourless
...
(No d-d transitions can occur)
...

What is the role of CO2 being bubbled through manganate (VI) ion disproportionation?

It lowers the pH of the solution
...

Explain the term bidentate ligand
...

How does insufficient acid in potassium magnate (VII) titration affect the result?

If the dilute sulphuric acid isn’t added in excess, it results in the production of MnO2 which is a brown
precipitate and masks the end point of the titration
...

Suggest how barium diphenylamine sulfonate acts as an indicator in an iron chromium redox reaction
...
The colour changes arises because the Fe2+ that is initially present
in excess acts as a reducing agent of the indicator, then when there are no more Fe2+ ions present it’s no
longer being reduced so the colour change occurs which is the end point
...


Ethanol can be easily oxidised and so requires less dichromate to be oxidised and hence would decrease
in the titre volume for the expected concentration
...
Whereas the sodium
ion has strong forces of attraction between slight charges on the water molecules and whole positive
charge on the sodium ion
...

Suggest how aluminium ions are able to form complexes
...

Suggest how interactions of the transition metal ion and ligand can result in a colourless complex, even if
there is as partially filled d subshell
...
When there are strong attractions between the ligand and the
ion it can split the subshell to a greater wavelength the visible light region and hence no colour can be
seen
...

Where is a species oxidised at in an cell?

The cathode is the positive electrode, which is the RHS of a calculation, hence the oxidising agent, where
itself the species is reduced
...

Explain why a complex coloured
...

Explain why amines are less soluble as the molar mass increases
...

What does the oxidation number of an element mean?

It’s the charge the atom would have if its bonding electrons were completely transferred
Why would a cell display a zero value?

The reaction system is in equilibrium
...


It’s a highly charged ion, and would polarise the water breaking the OH bond
...


The remaining outer p orbital electron of the carbon is delocalised into the pi system, which results in
more energy required to break the bonds in benzene compared to three C=C bonds making the molecule
more stable than expected
...


X-ray diffraction provides evidence that benzene molecules have carbon-carbon bonds that are all the
same length, whereas in Kekule structure the alternating double and single bonds are different lengths as
C=C is shorter length than C-C bonds
...

Why does glycine have a relatively high boiling temperature for such a small molecule?

The zwitterion of glycine has oppositely charged ends, which would be attracted to each other, forming
ionic bonding between molecules forming a solid lattice structure, hence with a high boiling temperature
...

Explain why using a catalyst and microwave heating is considered β€˜greener’
...
Electrical energy can be obtained from renewable
resources whereas gases are non-renewable
...

Outline how to purify a solid by recrystallization, explaining each step
...
The filtrate is then
cooled and crystals form and soluble impurities can be filtered and washed off the crystal
...


Some of the reagent used to fill the jet (which doesn’t react with the iodine solution) and so the titre is
too high therefore so would the mean titre
...

What effects strength of intermolecular forces?

The larger the mass of the molecule the greater the number of electrons and hence the stronger the
London forces
...

Why can phenol be nitrated in milder conditions

Benzene ring in phenol has greater electron density as O donates electron density to the ring because the
lone pair of electrons on the oxygen in phenol overlaps and interacts with the benzene ring
...
The soluble impurities are removed by cold
filtration
...


Ethanol has hydrogen bonding as well as London forces, ethoxyethane has London forces and dipole
dipole forces so more energy is required to separate ethanol molecule as the hydrogen bonds are much
stronger, comparatively to ethoxyethane
...

How does an amine group give the molecule basic properties, and how the strength of basicity differs between
phenylamine and alkyl amine
...
The amine group bonded to the benzene ring is much less basic as the lone par on the
nitrogen interacts with the pi system of the benzene ne ring
...

Why is HPLC used to check purity of a substance compared to nmr?

In HPLC there will be one peak for each component of the mixture
...

Suggest why stereospecific synthesis is used in pharmaceutical industry?

To avoid having to separate the unwanted enantiomer
...
The other
enantiomer may be harmful/ toxic/hazardous
...

Describe the technique of steam distillation and an advantage of it over normal distillation
...
The
advantage is that it prevent decompositions and product distils at a lower temperature
...


If the molecule is non-chiral then there isn’t a racemic mixture and enantiomers don’t have to be
identified and separated and discarded, which results in a higher atom economy
...

What’s the feature of an amine molecule allows to act as a base?

The lone pair of electrons on the nitrogen atom is able to accept a proton by forming a dative covalent
bond with the hydrogen ion
...


Spectroscopy, or measure the melting temperature and compare with known value from a data book
...


Hydrogen bonds would exist between the hydrogen atoms bonded to the nitrogen atoms and the lone
pair of electron of the either the oxygen or nitrogen
...
Finally there are London forces between chains as there are a large
number of electrons giving rise to induced/ temporary dipoles
...
Tertiary amines aren’t more accepting than secondary because the from
a corresponding ammonium salt which aren’t very soluble in water and hence is less basic
...


A suitable solid to absorb water would be anhydrous calcium chloride or silica gel
...


55

Edexcel

A2 Chemistry

Revision Notes

Why would a fewer step synthesis be β€˜greener’?

There are less reactants required, less waste at the end of each step
...

Briefly describe how you would use chromatography to identify amino acids in a hydrolysed protein mixture
...
Run in a solvent in one
direction, then rotate and repeat
...
Compare amino acid Rf values to known values and identify
...
Hence less exothermic and more energy required in the
system to break the bonds so less is given into the surroundings
...
Nitrogen/oxygen atom hydrogen bond to
the water molecules
...

What’s the distinguishing characteristic of combinatorial chemistry?

It allows simultaneous synthesis of many products that are different but related compounds
...

Why does benzene undergo substitution reactions rather than addition?

The delocalisation of the pi system electrons of the ring makes it more stable that an equivalent 1, 3, 5cyclohexatriene, and so substitution retains this stable arrangement
What does the stabilisation energy of benzene mean?

The enthalpy change for the conversion of benzene to cyclo-1, 3, 5-triene
What does steam distillation depend on?

The use of the technique depends on the compound forming two layers with water
...


56

Edexcel

A2 Chemistry

Revision Notes

Specification notes

CHEMISTRY UNIT 4
How fast? – Rates
a
...


c
...


e
...



...
Half-life is time taken for
reactant concentration to reduce to half of its initial value
...
Rate determining step is the slowest step of the reaction, which
hence controls how fast the reaction occurs
...

Colorimetry is effective technique in recording rate of reaction when there is a colour change at
the end point of the reaction
...
e
...
Volume change is used when a gas is produced as well but more
suitable for gases such as hydrogen
...

By plotting the progress of the reaction, it can be used determine the rate of reaction and hence
its half-life
...

For a concentration time graph: if the gradient is constant, shows rate is unaffected by
concentration and is hence zero order and half-life decreases as concentration decreases; if the
gradient is exponential then reaction is first order and half-life is constant; if the gradient is
much steeper then rate is second order and half-life increases as the concentration falls
...

Reaction between propanone and iodine; varying the concentration of iodine hydrogen and
Propanone gives the order of the species, trimetric and colorimetry can be sued to monitor the
iodine concentration
...
This indicates that iodine must be
involved in an additional faster step not involved in the rate determining step
...

With a first order reaction the half-life will remain constant
ii
...

iii
...


v
...

The Arrhenius equation can be used to calculate the activation energy by using
graphical methods
...


g
...
An example is the oxidation of iodide
ions to iodate (V) ions in acidic solution
...

h
...

i
...
These are consistent with experimentally
determined rates of reaction
...
A primary haloalkane goes via a second order nucleophillic substitution SN2 mechanism, where
both species are in the rate equation and it goes via a one-step mechanism, via a pentavalent
intermediate, where the nucleophile bond opposite to the leaving group
...

Where the C-halogen bond break initially being the slow rate determining step the substitution
step is a faster step and hence isn’t represented in the rate equation
...


How far? – Entropy
a
...
Entropy is a measure of disorder in system, the more disordered the greater the entropy
...
If the number of moles of product is greater than reactants then this increases the
arrangements of quanta, leading to an increase entropy change
...
Entropy increases with temperature as entropy increases as molecules change state from solid > liquid -> gas
...
e
...
A perfect crystal at zero kelvin, entropy is zero
...
The physical state of the molecule mainly dictates its standard entropy value however also
depend on the complexity to an extent, in term of energy quanta
e
...
Such as ionic solid sodium chloride, dissolved in
solution increaser the entropy and is more favourable
...


The natural direction is an increase in entropy
...
Experiments relation to disorder and enthalpy changes:
i
...

When a gas is evolved in a reaction there is a change in state and hence an increase in
entropy
iii
...

In mixing two solids, the entropy change will depend on the physical state of product of
produce or the number of moles of product produced
h
...
The entropy change if the system is given in the entropy data
j
...
The feasibility of a reaction depends on both these entropy changes and the greater the
temperature the smaller the value of entropy change of surroundings is and hence effects the
total entropy change less
...
Thermodynamic stability is dependent on the enthalpy change of a reaction
...
However a high activation
energy may prevent a spontaneous reaction occurring such as combustion requiring an ignition,
this is where reactants are kinetically inert
...
The total entropy change of an endothermic being positive shows it’s possible to occur at room
temperature
...

n
...
Hydration enthalpy is the enthalpy change when one mole of gaseous ions dissolve
in sufficient water to form an infinitely dilute solution
...

βˆ†π» π‘ π‘œπ‘™π‘’π‘‘π‘–π‘œπ‘› = βˆ’ βˆ†π» π‘™π‘Žπ‘‘π‘‘π‘–π‘ π‘’π‘›π‘’π‘Ÿπ‘”π‘¦ + βˆ†π»β„Žπ‘¦π‘‘π‘Ÿπ‘Žπ‘‘π‘–π‘œπ‘›
o
...
Hydration enthalpy; smaller ions have a
greater charge density and larger charges increase charge density, which attracts more polar
water molecules which are exothermic
...
A positive βˆ†π» π‘ π‘œπ‘™π‘’π‘‘π‘–π‘œπ‘› is overall endothermic and therefore isn’t favoured in term of enthalpy,
however from a very low entropy value for the ionic lattice upon dissolving the liquid increase
the entropy and the entropy change favours the reaction
...
Dynamic equilibrium is when the rate of the forwards reaction is equal to the reverse and the
concentration of reactants and products remains constant
...
Many industrial processes are reversible reactions, such as Haber process

59

Edexcel

A2 Chemistry

Revision Notes

c
...
The value of Kc can then be calculated by given data, if the state of the reactant/ product is a
solid the concentration is taken to be constant and hence aren’t used to calculate the
equilibrium constant
...
A gaseous equilibrium constant can be calculated Kp, using partial pressures, which are defined
as mole fractions: π‘šπ‘œπ‘™π‘’ π‘“π‘Ÿπ‘Žπ‘π‘‘π‘–π‘œπ‘› =

π‘›π‘’π‘šπ‘π‘’π‘Ÿ π‘œπ‘“ π‘šπ‘œπ‘™π‘’π‘  π‘œπ‘“ 𝐴
π‘‘π‘œπ‘‘π‘Žπ‘™ π‘›π‘’π‘šπ‘π‘’π‘Ÿ π‘œπ‘“ π‘šπ‘œπ‘™π‘’π‘  𝑖𝑛 π‘šπ‘–π‘₯π‘‘π‘’π‘Ÿπ‘’

from which the partial

pressure is calculated: 𝑃 𝐴 = π‘šπ‘œπ‘™π‘’ π‘“π‘Ÿπ‘Žπ‘π‘‘π‘–π‘œπ‘› Γ— π‘‘π‘œπ‘‘π‘Žπ‘™ π‘π‘Ÿπ‘’π‘ π‘ π‘’π‘Ÿπ‘’, hence 𝐾𝑝 =

𝑃𝐢 𝑐 +𝑃𝐷 𝑑

...

f
...
𝐾 𝐢 < 1, the reactants are favoured and equilibrium position lies well over the reactant side vice
versa, 𝐾 𝐢 > 1 Γ— 1010 means reaction has virtually gone to completion and hence 𝐾 𝐢 <
1 Γ— 10βˆ’10 little/ no reaction has occurred
...
For an exothermic reaction as T increases, lnK become smaller, this means less product in the
reaction
...


Applications of rate and equilibrium
a
...
Which alters reactions
according to the La Chatelier’s principle
b
...
However
industrial processes aren’t in reality in equilibrium as product is removed upon formation
...
Atom economy in industry is improved by finding more efficient synthesis methods, or finding a
use for the by-product and recycling unreacted reagents
d
...


Acid/ base equilibria
a
...
This
stated acids gave hydrogen ions in solution and bases gave hydroxide ions
...
However the wider definition, BrΓΈnsted-Lowry definition states acid is a substance that donates
protons and a base is a substance that accept protons
...
Acid-base pairs are defined as species that change into each other by gaining or losing a proton
...

d
...
Ka is acid dissociation constant of equilibrium and in a strong acid [𝐻 + ] =
[π‘Žπ‘π‘–π‘‘]
...
Ionic product of water defined as 𝐾𝑀 = [𝐻 + ][𝑂𝐻 βˆ’ ] = 1 Γ—
10βˆ’14 π‘šπ‘œπ‘™ 2 π‘‘π‘šβˆ’6
...

e
...
Hence πΎπ‘Ž =

+
[𝐻(π‘Žπ‘ž) ][π΄βˆ’ ]
(π‘Žπ‘ž)

[𝐻𝐴(π‘Žπ‘ž) ]


...


Analyse results from experiment:
i
...
pH calculations can be used to compare a variety of substances
...

ii
...

g
...
For a weak acid pH calculation two assumptions
are made [𝐻 + ] = [π΄βˆ’ ] and concentration of HA remains constant
...


h
...
Similar assumptions made

for weak acid are made for weak base calculations
...
pH changes during a titration can be plotted giving a titration curve
...

j
...
Vertical sections for the
following: strong acid-strong base (4-10), weak acid-strong base (6
...
5), weak acid-weak base (NO vertical section)
...
A buffer solution is where the pH doesn’t change significantly if small amounts of acid or alkali
are added
...
[𝐻(π‘Žπ‘ž) ] =

πΎπ‘ŽΓ—[𝐻𝐴(π‘Žπ‘ž) ]
[π‘ π‘Žπ‘™π‘‘ π‘–π‘›π‘–π‘‘π‘–π‘Žπ‘™ ]


...

l
...

m
...
This is extremely
important in for example the blood (a carbonic acid-hydrogen carbonate equilibrium acts as a
buffer to control pH after eating a particularly acidic food for example to ensure pH remains
virtually the same) which disrupts biochemical reactions and could result in death
...


Further organic chemistry
1 Chirality
a
...
Optical isomers are formed when a molecule has a chiral centre in the molecule, where a carbon
atom has four different groups bonded to it
...
Optical activity is exhibited when a single optical isomer is able to rotate a plane of polarisation
of plane polarised monochromatic light
...
Light is rotated
equally and in opposite directions and hence no optical activity
...
Optical activity can change after undergoing s SN1 or SN2 substitutions and in additions to
carbonyl compounds
...
e
...


2 Carbonyl compounds
a
...
The polar carbonyl group in aldehydes and ketones mean there are dipole-dipole interactions,
but don’t partake in hydrogen bonding
...
However in a polar solvent such as water carbonyl group allows
hydrogen bonding, as chain size increases solubility decreases
...
Reactions of carbonyl compounds:
i
...
These positive results only occur with aldehydes, no
effect with ketones
ii
...

The is a slight positive charge of the carbon of the carbonyl group, which susceptible to
nucleophillic attack, such as cyanide, KCN gives a higher con
...
Often produces
a molecules with a chiral centre and hence optically active however doesn’t display this
because the nucleophile is equally likely to attack above or below the trigonal planer
carbocation intermediate
...

2, 4-DNP adds to the carbonyl group and eliminates water, this is a test for a carbonyl
group in a compound
...

v
...
Carboxylic acid general formula; RCOOH
b
...
They are also very soluble due to being able to form
hydrogen bonds with solvent such as water
c
...
Reaction of carboxylic acids:
i
...

Neutralisation of the acid gives a carboxylate salt
iii
...

Esterification with an alcohol and under acidic condition produces an ester and water

4 Carboxylic acid derivatives
a
...
Reaction of acyl chlorides:
i
...

Reacts with alcohols to produce an ester and HCl, more effective than carboxylic acid as
it goes to completion
iii
...
Ammonia produces acid amides as products formula: RCONH2
iv
...
Reactions of esters:
i
...

Alkaline hydrolysis, ester and a base, gives a carboxylate salt and an alcohol
iii
...
e
...
Trans-esterification is used as
an alternative of hydrogenation to hardening fats, producing fewer harmful trans-fats
...
This is seen as a potentially greener fuel alternative
...
Polyesters are condensation polymers, where ester monomers form with monomers such as a
diols and dicarboxylic acids and produce a small molecule as an additional product, usually
water
...


Spectroscopy and chromatography
a
...

Infrared radiation is absorbed by molecules at different bonds/ functional groups absorb
the radiation at different frequency, to distinguish between two or more compounds
they must have strong absorption peaks on which the other doesn’t i
...
O-H
ii
...

Radio waves in nmr, hydrogen nuclei absorb radio wave frequency, this can be sued to
determine the structure as protons in different environments have different chemical
shifts and relative abundancies
iv
...
How nmr can identify structure of a molecule:
i
...
Different hydrogen environments are in
regions of shift
ii
...

Protons spin about their axis and when hydrogen nucleus absorbs the radio wave
frequency it aligns with the magnetic field
iv
...
Infrared can be used to check the progress of a reaction, as the functional groups change
...
Mass spectra can be used to identify possible structure as fragmentation patterns will give the
indication of groups present and ones that aren’t, heights are relative abundance, most right
peak id parent ion peak and charge is taken as one for m/z value
...
Gas chromatography separate volatile compounds, and the retention time (time taken to travel
through the column) can be compared to known sample values
...
Components can be washed off using a solvent and UV can
be sued for further analysis
...


64

Edexcel

A2 Chemistry

Revision Notes

CHEMISTRY UNIT 5
Application of redox equilibria
a
...
Redox is where oxidation and reduction occurs in the
same reaction
...
L,
b
...
e
...

c
...
A standard hydrogen electrode is an
equilibrium of hydrogen gas and H+ ions, with hydrogen gas at 1atm pressure, solution at
1moldm-3 and at 298K
...

d
...
Where the RHS is the most positive value and the most
powerful oxidising agent
...

e
...
Hence since promotional to entropy, even if it is greater than zero, reaction may not occur
spontaneously due to kinetic inertness, as discussed in unit 4 entropy
...
Using the standard electrode potentials of elements with various oxidation states, and
reagents such as iron experiments can be undertaken to successively reduce or oxidising
observing colour changes such as with vanadium
h
...
The potassium manganate (VII) titration, is a redox reaction between MnO4- and Fe2+, which is
self indication (if manganate is in burette then colourless to purple)
...
There is an excess of sulphuric acid added so the titration isn’t greater than expected
and end point masked by the MnO2 that would be produced which is a brown precipitate
...
Thiosulfate redox is between I2 and S2O32-, which uses a starch indicator, added towards the end
as otherwise a blue complex form with high concentrations of iodine which is insoluble and
doesn’t redissolve upon excess thiosulfate so indeterminate endpoint
...

i
...

65

Edexcel

A2 Chemistry

Revision Notes

j
...
They produce a continuous voltage as fresh reactants are fed in,
maintaining a constant concentration
...
Has greater efficiency, since direct conversion to electric
...

k
...
IR is also used which can determine amounts of
alcohol from its spectrum, more alcohol greater absorbance
...
The use of fuel cells and IR can
be used in prosecution in many countries
...
A d block element is defined as having its outer shell electron in the d subshell, where as a
transition metal is also a d block element but also forms one or more stable ions with a partially
filled 3-d orbital
...
Across the 3-d block the electronic configuration follows the expected pattern of filing the 4S
subshell then consecutively filling the 3d
...
This is a more stable arrangement by minimising repulsion between paired
electrons
...
Electronic structure or the elements can be backed up y looking at the successive ionisation
energies of elements, i
...
a big jump indicates where the electron is the last removed form a half
filled or empty subshell, requiring more energy due to the increase in nuclear change to
attraction ratio
...
General properties of transition metal elements include:
i
...
They can form coloured ions in solution, as the d subshell spilt visible light region of
electromagnetic spectrum is absorbed at that specific wave length the light is absorbed
and the remaining colour that can be seen is its complimentary colour
iii
...

iv
...

e
...
the chemistry of chromium and copper, including properties and reactions:
i
...
[𝐢𝑒(𝐻2 𝑂)3 (𝑂𝐻)3 ](𝑠)
- Reacts with an acid to form [πΆπ‘Ÿ(𝐻2 𝑂)6 ]3+ and with a base to give [πΆπ‘Ÿ(𝑂𝐻)6 ]3βˆ’
...
Sulphuric acid, copper reacts forming copper (II) sulphate, with bright blue
hydrated ions:
𝐢𝑒(𝑠) + 2𝐻2 𝑆𝑂4(𝑙) β†’ 𝐢𝑒𝑆𝑂4(π‘Žπ‘ž) + 𝑆𝑂2(𝑔) + 2𝐻2 𝑂(𝑙)
...
HCl:
βˆ’
𝐢𝑒𝐢𝑙(𝑠) + 𝐢𝑙(π‘Žπ‘ž) β†’ [𝐢𝑒𝐢𝑙2 ]βˆ’
(π‘Žπ‘ž)
Copper (I) chloride is prepared by boiling copper (II) chloride with conc
...
Initially
tetrachlorocuprate (II) complex ion is formed:
βˆ’
[𝐢𝑒(𝐻2 𝑂)6 ]2+ + 4𝐢𝑙(π‘Žπ‘ž) β†’ [𝐢𝑒𝐢𝑙4 ]2βˆ’ + 6𝐻2 𝑂(𝑙)
(π‘Žπ‘ž)
(π‘Žπ‘ž)
This is then reduced to the dichlorocuprate (I) ion by boiling with copper:
[𝐢𝑒𝐢𝑙4 ]2βˆ’ + 𝐢𝑒(𝑠) β†’ 2[𝐢𝑒𝐢𝑙2 ]βˆ’
(π‘Žπ‘ž)
(π‘Žπ‘ž)
When this mixture is poured into cold water a white precipitate forms of copper (I) chloride:
βˆ’
[𝐢𝑒𝐢𝑙2 ]βˆ’ β†’ 𝐢𝑒𝐢𝑙(𝑠) + 𝐢𝑙(π‘Žπ‘ž)
(π‘Žπ‘ž)
Copper (I) iodide is precipitated as a white solid:
𝐢𝑒𝑆𝑂4(π‘Žπ‘ž) + 4𝐾𝐼(π‘Žπ‘ž) β†’ 𝐢𝑒𝐼(𝑠) + 2𝐾2 𝑆𝑂4(π‘Žπ‘ž) + 𝐼2(π‘Žπ‘ž)
Copper (I) oxide is precipitated as a red solid when an alkaline solution of copper (II) sulphate
βˆ’
2+
𝐢𝑒(π‘Žπ‘ž) + 2𝑂𝐻(π‘Žπ‘ž) + 2𝑒 βˆ’ β†’ 𝐢𝑒2 𝑂(𝑠) + 𝐻2 𝑂(𝑙)
ii
...
Both copper and chromium from stable complexes with a range of ligand
including water, chlorine ammonia hydroxide ions etc
...
Many aqueous transition metal ions and complexes have a colour
...

Hence if the d subshell is full a colour isn’t visible as well as if the ligand on the ion is
strongly bonded can result in a larger splitting outside the width of the visible light region
and colour cannot be seen as well
...
Ligands undergo exchange reactions dependent on the relative strength, such as water
ligands can be substituted from hydroxide ligands
...
The stability of a complex can be inked to the idea of entropy; an example is a hexaaqua
complex undergoing ligand exchange with a poly dentate ligand such as EDTA
...

vi
...

g
...
Copper exchange reaction can be carried out, in which colour changes are seen
dependent on reagents used i
...
blue to green upon chlorine addition to hexaaqua
complex
...
Oxidation states can be investigated in chromium by successive reduction of Cr6+ using a
string reducing agent such as zinc in acid solution
...


67

Edexcel

A2 Chemistry

Revision Notes

iii
...

h
...
They can
use 3d and 4s electrons of atoms on the metals surface to form weak bonds to the reactants
(how reactants are absorbed onto catalyst active sites)
...

i
...
The scientific community validates new discoveries by peer reviewed published
journals
...
Transition metals react with sodium hydroxide and ammonia to from various complexes, with a
little added or when in excess
...

Consult table for specific detail
...
Amphoteric behaviour can be seen in reactions as an equilibrium of acid and alkaline, whereas a
ligand exchange goes to completion and the ligands become permanently exchanged
...
Transition metals have other applications that include photochromic sun glasses, which sunlight
shifts the equilibrium Cu+(s) + Ag+(s) β‡Œ Cu2+(s) + Ag(s)
...


Arenes: benzene
a
...
Several pieces of
evidence support this structure
...
e
...
X-ray diffraction shows bond lengths between carbon
atoms are all equal in benzene where as double bonds are shorter than single that wouldn’t be
true for Kekule structure
...
indicating
there’s not a double bond present
b
...

Combustion, which burns yellow with a smoky flame, this is due to a high carbon to
hydrogen ration in the molecule, which lends itself readily to incomplete combustion
...

Reaction with bromine occurs rapidly in presence of UV light:

68

Edexcel

A2 Chemistry

Revision Notes

iii
...


iv
...


Acylation and alkylation (Friedel crafts reactions) follow very similar mechanisms
...


Addition reaction occurs with hydrogen to produce cyclohexane, in the presence of a
Raney nickel catalyst
...
Benzene undergoes readily electrophile substitution reaction, due to large electron density form
the delocalised pi system
...

+
βˆ’
𝐢𝐻3 𝐢𝐻2 𝐢𝑙 + 𝐴𝑙𝐢𝑙3 β†’ 𝐢𝐻3 𝐢𝐻2 + 𝐴𝑙𝐢𝑙4
d
...

e
...
Phenol also reacts with nitric acid without the need for
sulphuric acid catalyst like benzene, at room temp
Title: Edexcel A2 Chemistry revsion notes
Description: made during revision of A2 exams. contains detailed revision notes for both unit 4 and 5 edexcel chemistry made from both revision guides and textbook and lesson notes. questions and model answers from past papers jan 2010- jan 2015. included also specification specific notes with answers to each specific point to the specifications, concise version of revision notes. total 69 pages.
Buy These NotesPreview