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CHEMISTRY

UNIT 3
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At least one species is oxidised, and at least one is
reduced
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The standard electrode potential (SEP, 𝐸 𝜃 ) is measured under standard conditions
(298k, 101kPa, 1 moldm-3) and against a standard hydrogen electrode
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To create an electrochemical cell, you connect two electrodes, by means of a salt bridge and a high
resistance voltmeter
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The oxidised species is on
the left, the reduced species is on the right
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A comma
represents two species of the same state
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The feasibility of every redox reaction is based on the EMF of the reactants
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If it’s negative, it won’t happen
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Hydrogen fuel cells are just electrochemical cells that use the oxidation of hydrogen and the
reduction of oxygen
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The disadvantages is that hydrogen is very explosive, and hard to store
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2: REDOX REACTIONS

You can create a stoichiometric equation by creating two half equations, and then combining them,
for example:
𝐶𝑟2 𝑂7 2− + 14𝐻 + + 6𝑒 − → 2𝐶𝑟 3+ + 7𝐻2 𝑂
𝐹𝑒 2+ → 𝐹𝑒 3+ + 𝑒 −
𝐶𝑟2 𝑂7 2− + 14𝐻 + + 6𝐹𝑒 2+ → 2𝐶𝑟 3+ + 7𝐻2 𝑂 + 6𝐹𝑒 3+
Dichromate (VI) is reduced to chromate (III)
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Both must
be acidified
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5)
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UNIT 3
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This means they can act as an acid and as a base
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𝐴𝑙2 𝑂3 + 6𝐻𝐶𝑙 → 2𝐴𝑙𝐶𝑙3 + 3𝐻2 𝑂
𝐴𝑙2 𝑂3 + 2𝑁𝑎𝑂𝐻 + 3𝐻2 𝑂 → 2𝑁𝑎[𝐴𝑙(𝑂𝐻)4 ]
𝑃𝑏𝑂 + 2𝐻𝑁𝑂3 → 𝑃𝑏(𝑁𝑂3 )2 + 𝐻2 𝑂
𝑃𝑏 2+ + 4𝑂𝐻 − → 𝑃𝑏(𝑂𝐻)2−
4
The inert pair effect is the tendency of the s shell electrons of a p block element to remain
unbonded
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Carbon mainly forms the 4+ ion, while
lead’s most stable ion is 2+
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As a result of this, lead IV is less stable than lead II, so lead IV will act as an oxidising agent
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Group three elements can form compounds with fewer than eight electrons in their outer shell
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This gives
compounds such as 𝐴𝑙𝐶𝑙3 and 𝐵𝐹3
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An aluminium chloride monomer bonds with itself to form a dimer, which gives the
formerly electron deficient aluminium eight electrons in it’s outer shell
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This is because one of the s electrons is promoted to the d shell, so
there’s two more electrons available for bonding
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Hexagonal BN has a structure comparable
to graphite
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Unlike graphite, it isn’t a good conductor, as it has no free electrons
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It can be used crucibles and other reaction vessels, and also as insulators in
electrical circuits
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It is very hard, and has a high melting
point
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It can be used in drills, and also as a
catalyst
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The main reason for
this is that carbon has no d shell, so the intermediary stage of the reaction is very difficult, so the
reaction has a high activation energy
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The reaction of lead chloride and water gives lead ions as a product
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𝑃𝑏 2+ + 2𝑂𝐻 − → 𝑃𝑏(𝑂𝐻)2
𝑃𝑏(𝑂𝐻)2 + 2𝑂𝐻 − → 𝑃𝑏(𝑂𝐻)2−
4
Lead chloride is a white precipitate, and lead iodide is yellow
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If it’s cold, the
reaction will be:
𝐶𝑙2 + 𝑁𝑎𝑂𝐻 → 𝑁𝑎𝐶𝑙 + 𝑁𝑎𝑂𝐶𝑙 + 𝐻2 𝑂
This is a disproportionation reaction
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If it’s warm, the reaction will be:
3𝐶𝑙2 + 6𝑁𝑎𝑂𝐻 → 5𝑁𝑎𝐶𝑙 + 𝑁𝑎𝑂3 𝐶𝑙 + 3𝐻2 𝑂
This is also a disproportionation reaction, but you get the chlorate(V) ion instead of the chlorate(I)
ion
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They can be used as bleach
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The hydrogen chloride isn’t a strong enough reducing agent to affect the sulphur
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Hydrogen bromide, however, can reduce sulphur
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The sulphur
form the acid is reduced from +6 to +4
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Hydrogen iodide is an even stronger reducing agent than bromine
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The products are iodine, hydrogen sulphide and water
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UNIT 3
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This is because there are no
large jumps in ionisation energies, so it’s easy for more or fewer electrons to be lost
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This can then coordinate bond with a metal
ion, forming a complex
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Without an attached ligand, the metal’s d orbital pairs all have the same energy
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Two pairs have a higher energy, and three pairs have a lower energy
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The colour of light that’s absorbed
isn’t seen, so the substance appears to be the opposite colour
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Ligands are often exchanged for others, and the coordination number
can change
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The
coordination number goes form six to four, and the solution goes from
blue to green
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Name

Formula

Colour
2+

Hexa-aqua-copper

[𝐶𝑢(𝐻2 𝑂)6 ]

Light Blue

Tetra-amine-di-aqua-copper

[𝐶𝑢(𝑁𝐻3 )4 (𝐻2 𝑂)2 ]2+

Deep Blue

Tetra-chloro-copper

[𝐶𝑢(𝐶𝑙)4 ]2−

Green

Hexa-aqua-cobalt

[𝐶𝑜(𝐻2 𝑂)6 ]2+

Pink

Tetra-chloro-cobalt

[𝐶𝑜(𝐶𝑙)4 ]2−

Blue

Transition metals are also very useful as catalysts
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Adsorption is when something sticks to a surface
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Homogenous catalysts form temporary bonds with the reactants, which
provides a quicker/easier route for the reaction
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Nickel is a catalyst for the hydrogenation of alkenes
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Vanadium (V) oxide is used in the contact process, to make sulfuric acid
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Metal
Chromium (III)
Iron (II)
Iron (III)
Copper (II)

Colour before adding excess OHBlue
Pale Green
Pale Brown
Blue

Colour after adding excess OHGelatinous Green
Dirty Green
Red/Brown
Blue

UNIT 3
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At regular intervals a sample is taken
form the mixture, and cooled quickly to stop the reaction
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This can be used for most reactions, but is a very labour intensive and possibly
inaccurate method
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The total
order of the equation is 𝑙 + 𝑚 + 𝑛
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The order of each reactant can be found by repeating the experiment with different concentrations
of that reactant, and seeing how it affects the rate
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If doubling concentration doubles rate, it’s first order
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If an equation has multiple steps, the rate is determined by the slowest one
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If an equation has a 0 order reactant, then it must have a rate determining step
which doesn’t include that reactant
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We can then deduce that the what happens is:
𝑁𝑂2 + 𝑁𝑂2 → 𝑁𝑂3 + 𝑁𝑂 (𝑠𝑙𝑜𝑤 𝑠𝑡𝑒𝑝)
𝐶𝑂 + 𝑁𝑂3 → 𝐶𝑂2 + 𝑁𝑂2 (𝑓𝑎𝑠𝑡 𝑠𝑡𝑒𝑝)
The rate determining step must include nitrate and not include carbon monoxide
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𝐸𝑎

𝑘 = 𝐴𝑒 𝑅𝑇
Where A is the frequency factor, Ea is the activation energy, R is the molar gas constant, and T is the
temperature
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The log of the equation can be plotted as a straight line graph:
(𝑌)ln(𝐾) = (𝑀)

𝐸𝑎
1
× (𝑋) + (𝐶)ln(𝐴)
𝑅
𝑇

UNIT 3
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g
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g
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Enthalpy change of solution is the energy released when an ionic solid is dissolved in water, e
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:
2+
−
𝑀𝑔𝐼2(𝑠) → 𝑀𝑔(𝑎𝑞)
+ 2𝐼(𝑎𝑞)

Enthalpy change of hydration is the energy released when one mole of gaseous ions is changed into
aqueous ions, e
...
:
2+
2+
𝑀𝑔(𝑔)
→ 𝑀𝑔(𝑎𝑞)

For a substance to dissolve, the lattice must break, which is an exothermic process, and then the
ions must become hydrated, which is an endothermic process
...


The Born-Haber cycle shows how the enthalpy change of lattice formation is calculated
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If Δ𝐻𝑓𝑜 is endothermic, then the
compound will be unstable
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7: ENTROPY AND FEASIBILITY OF REACTIONS

S is the entropy of a system
...
Entropy always wants to increase
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You can find the change in
entropy by using the equation:
Δ𝑆 = 𝑆𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 − 𝑆𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠
The feasibility of a reaction is governed by its Gibbs free energy (Δ𝐺)
...
If Δ𝐺 is negative, then the reaction is feasible
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This shows how endothermic
processes can occur
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UNIT 3
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In an
endothermic reaction, as temperature increases, product increases, so Kc increases
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In an
endothermic reaction, as temperature increases, product increases, so Kp increases
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UNIT 3
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A base is a proton acceptor
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It has a low pH, a high Ka , and a low pKa
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e
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𝑖𝑛 𝑎 𝑝𝑢𝑟𝑒 𝑎𝑐𝑖𝑑, [𝐻] = [𝐶𝑙], 𝑠𝑜 𝑡ℎ𝑒 𝑡𝑜𝑝 𝑐𝑎𝑛 𝑏𝑒 𝑟𝑒 − 𝑤𝑟𝑖𝑡𝑡𝑒𝑛 𝑎𝑠 [𝐻]2

The pKa is essentially the pH of the Ka
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The Ka of water is the Kw and is, at room temperature, 10-14
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The equivalence reaction of an acid base reaction is the point at which the reaction completes
...
The pH equivalence point is the
midpoint of the vertical line which shows the reaction being completed, e
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The indicator is selected based on the range of pH in which it changes colour - it must fit with the
equivalence point
...
A
typical acidic buffer solution is sodium ethanoate and ethanoic acid
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When a
base is added, the OH ions react with the acid to form water and the ethanoate ion
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An alkaline buffer would work in the same way, and a
typical example would be ammonia and ammonium chloride
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1: STEREOISOMERISM

Stereoisomers are molecules which have the same molecular formula and sequence of atoms, but
differ in 3D space
...
An optical isomer
has a chiral centre, i
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a carbon atom attached to four unique groups
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An enantiomer rotates
the plane of polarized light
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An example of enantiomers is:

UNIT 4
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An aromatic hydrocarbon is one in a ring, e
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benzene
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g
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Benzene is a ring of 6 carbon atoms, each bonded to one hydrogen
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The fourth electron is found delocalised in a cloud of electron density above and below the ring
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This delocalised structure makes benzene more stable than
something like hexane
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Benzene, however, does do electrophilic substitution
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The mechanism is slightly different, however, as the ‘pi bond’ in
the benzene doesn’t break
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This is very unstable
however, and the hydrogen soon bonds with the negative ion, leaving an electron behind
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Nitrobenzene is yellow
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g
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It happens at room temperature
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The Friedel-Crafts alkylation of benzene involves
adding the chloroalkane in the presence of aluminium chloride
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Chlorobenzene, however,
requires high temperatures and pressures to complete the same reaction
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UNIT 4
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To do this you can add LiAlH4 in dry
conditions, dissolved in ethoxyethane
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To form an alcohol from a halogenoalkane, you reflux with sodium hydroxide
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When a phenol or an alcohol is reacted with ethanoyl chloride, an ester is formed
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When an alcohol (but NOT a phenol) is refluxed with sulfuric acid and a carboxylic acid, an ester is
formed
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A white precipitate is
formed, and the bromine water is decolourised
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A phenol will form a violet precipitate
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4: ALDEHYDES AND KETONES

Ketones and aldehydes can be formed from the oxidation of alcohols
...
A primary alcohol will give an aldehyde and a secondary alcohol will give a
ketone
...

You can tell the difference between an aldehyde and a ketone because an aldehyde is easy to
oxidize, and a ketone isn’t
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The aldehyde will change it from orange to green
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This is because the silver is
reduced
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Aldehydes and ketones can undergo nucleophilic addition
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The O takes the
electron
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If 2,4 DNP is added to an aldehyde or a ketone, then an orange precipitate is formed
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You could also dry the precipitate, and then find its melting point
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The iodoform reaction (heating with hydroxide and iodine) will give a yellow crystalline solid when
reacted with a methyl-oxygen group, for example a 2-one, 2-ol, ethanol, ethanal
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5: CARBOXYLIC ACIS AND THEIR DERIVATIVES

The order of acidity, from least to most is: alcohol, water, phenol, carboxylic acid
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In alcohols, the carbonyl group is electron releasing, meaning that the negative charge is pushed
away, making the anion less stable
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In phenols, the negative charge of the oxygen is somewhat delocalised due to the benzene ring
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In the carboxylic acid, the negative charge is very delocalised between the two oxygens
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Carboxylic acids can be formed form the oxidation of alcohols and aldehydes
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When the reaction is complete, the mixture will go from orange to green
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This must be done in dry conditions, and in
ethoxyethane
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You can form an aromatic carboxylic acid through the oxidation of methyl-benzene
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The mixture is
refluxed, and the salt is formed
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Decarboxylation is when a carboxylic acid loses the equivalent of a carbon dioxide molecule
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You add soda lime (a mix of sodium hydroxide, calcium
hydroxide and calcium oxide) to the acid, and then heat it
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g
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To form an acyl chloride from a carboxylic acid, you add phosphorous (V) chloride in dry conditions
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To form an ester from a carboxylic acid, you reflux with an alcohol and sulfuric acid
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To form a nitrile from a halogenoalkane, you reflux with sodium cyanide in dry conditions
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Firstly, the nitrile reacts with water to form an amide
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If the hydrolysis of the amide is done under acidic conditions, carboxylic acid is formed along with
ammonium ions
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Nitriles can be reduced using LiAlH4, in dry conditions and in ethoxyethane
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UNIT 4
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Adding excess ammonia to a halogenoalkane
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First, the nitrobenzene is reacted with concentrated hydrochloric acid in the presence of a tin
catalyst
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This forms a phenyl-ammonium ion
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The NH2 in an amine has a lone pair, and can act as a proton acceptor, like ammonia
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The order of basicity, form least to most is: aromatic amine, ammonia, aliphatic amine
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The lone pair on the
aromatic amine is somewhat delocalised in the benzene ring, making them less available for
bonding
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This reaction is done at room temperature under dry conditions
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This is
nitrogen gas
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This ion is too
unstable in the aliphatic form, so is only formed in arenes
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This retains the N triple N bond, but a
phenol becomes attached at the other end
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The N triple N bond is what’s called a chromophore
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This is what gives azo dyes their colour - the reflected
wavelengths
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7: AMINO ACIDS, PEPTIDES AND PROTEINS

An alpha amino acid is one in which the COOH group is next to the amine group
...
This means part of the molecule is positively charged,
and part is negatively charged, but the overall charge is neutral
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In acidic conditions, the protons are attached to the carboxylic acid group, leaving
a positive ion and in basic conditions the hydroxide ions react with the ammonium ion to form
water, and a negative ion
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Amino acids are soluble in polar solvents and non soluble in non polar solvents
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The acid group of one react
with the amine group of another, giving what’s called a peptide link, which is the same as the
functional group of secondary amide
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It’s an example of condensation polymerisation
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The primary structure of a protein is a long straight chain of amino acids
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A tertiary protein is how the sheets and helixes fit together in three-dimensional space
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UNIT 4
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Condensation polymerisation
is when one small molecule, usually water or HCl, is eliminated during polymerisation
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A
dicarboxylic acid can be formed by the oxidation of cyclohexane
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Some of this is then converted to a diamine
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This gives a diamine
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It’s made form a dicarboxylic acid and a diol

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