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Chemistry
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Solid particles? The particles in a solid are packed closely together, fixed in their positions and
vibrate
Liquids? Liquids have a fixed volume, but they can flow and change their shape
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They can be compressed easily
Gas particles? The particles in a gas have on average, lots of space between them and move around
at high speed, randomly in any direction
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Eventually, the vibrations will be so strong that the
particles begin to break free from their neighbours
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How does a liquid evaporate?
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The hotter the liquid is, the faster its particles move
around
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Its
rate of evaporation increases
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If we monitor the temperature of a solid as it is heated, what will happen when the solid
reaches it’s melting point? The temperature will stop rising
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Which changes of state absorb energy? Melting and boiling
Which changes of state release energy? Freezing and condensing

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Gradually, particles will move from an area of high
concentration to an area of low concentration

Diffusion
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Experiment to show diffusion in gases? Bromine vapour jar
Diffusion takes place more quickly through gases than through liquids
Why? Because the particles of gas are moving much more rapidly, on average, than the
particles in a liquid
What effect does the weight of the gas particles have on the rate of diffusion? We can
conclude that small, light particles diffuse faster than light, heavy ones

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4 Atomic structure SEE NOTES IN FOLDER
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Atoms are made of? Protons, neutrons and electrons
Protons have a relative charge of? +1
Electrons have a relative charge of? -1
Neutrons? Neutrons have no electric charge
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How to atoms carry no overall charge? Atoms contain an equal number of protons and
electrons…

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? Up to eight electrons
How do you state electronic structure? Start with the lowest level, then each successive
energy level

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The way an element reactions depends upon… the number of electrons in its outer shell
All elements in a particular group (same number of electrons in its outer shell) react in a
similar way…
Group 0 of the periodic table contains? The noble gases
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6 Atoms and isotopes
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Relative mass of proton? 1
Relative mass of neutron? 1
Relative mass of electron? Very small, about 1/2000 of a proton or neutron
Explain what is meant by the term isotope… Isotopes are different forms of the same
element, which have the same number of protons but a different number of neutrons
Common pair of isotopes? Carbon-12 and Carbon-14
What are the properties of the two isotopes like? The two isotopes have identical chemical
properties, but their physical properties, such as density can differ…

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2 Percentages and formulae
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Percentage mass of an element in a compound = Ar × Number of atoms / Mr of whole
compound
Empirical formula?
o Find how many moles is in each substance
o Then turn these numbers into a radio in its simplest form
o This tells you the empirical formula

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4 Equations and calculations
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What can balanced symbol equations tell us? The number of moles involved in the reaction…
What else can we use balanced symbol equations for? To calculate masses of products and
reactants…
QUESTIONS NEED TO BE PRACTISED

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6 The yield of a chemical reaction
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What is the yield of a chemical reaction? The yield of a chemical reaction describes how
much product is made
How can we calculate the percentage yield?
Amount of product produced / maximum amount of product possible × 100%
Why do very few reactions have a 100% yield?
o The reaction may be reversible
o Some reactants may react to give unexpected or unwanted products
o Some of the product may le lost in handling or left in apparatus
o The reactants may not be pure
o Some of the desired product may be lost during separation from the reaction
mixture

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These ions have the electronic structure of a noble gas…
Metal atoms? Loose electrons and become positive ions
Non-metal atoms? Gain electrons and become negative ions


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3 Giant ionic structures
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Characteristics of ionic compounds? It takes a lot of
energy to break the many strong ionic bonds that
hold a giant ionic lattice together, so ionic
compounds have high melting points
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Can they conduct electricity? Ionic compounds will
conduct electricity when we melt them or dissolve them in water… Once the ions are
separated from the lattice, they are free to move around freely anywhere in the liquid
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They vibrate but
cannot move around –
it does not conduct
electricity
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Ions
are free to move around within the
molten compound – it does conduct
electricity
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Ions are free to
move around within the solution –
it does conduct electricity
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4 Covalent bonding
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How are covalent bonds formed? When atoms of non-metals share electrons with each
other
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Simple molecules or Giant Covalent
structures

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6 Giant covalent structures
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Characteristics of giant covalently-bonded structures? High melting and boiling points
Examples of giant covalent structures? Diamond, graphite, and silicon dioxide (silica)

Diamond – each carbon atom forms four covalent bonds… makes diamond the
hardest natural substance… used for drill tips
o Silicon Dioxide – This is what sand is made of… each grain is a giant structure of
silicon and oxygen
o Graphite – each carbon atom forms only three covalent bonds, which creates layers
which are free to slide over each other… so graphite is soft and slippery… there are
weak intermolecular forces between the layers
o How can graphite conduct electricity? Each carbon atom has one delocalised
electron which allow it to conduct heat and electricity
Other structures that carbon atoms can form? Fullerenes
What sorts of structures are formed? Large cage-like structures and tubes, based on
hexagonal rings of carbon atoms
o

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Sunshine triggers a chemical
reaction which breaks down dirt that lands on the window
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o Nanoparticles used in face creams are absorbed deeper into the skin… also used in
sun tan creams and deodorants
Risks…?
o Their large surface area makes them dangerous… If a spark is made by accident, this
may cause a violent explosion
o As we use them more, there is greater risk of them getting into the air… breathing in
tiny particles could damage the lungs
o Nanoparticles could enter the bloodstream this way or from use in cosmetic
products, with unpredictable effects

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9%
o Carbon dioxide 0
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Air is filtered to remove dust
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During cooling, water vapour is condensed and is removed
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The liquefied air then enters the fractionating column and is heated slowly
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Oxygen and
argon come out together so another column is used to separate them
Uses for nitrogen gas?
o Used in sealed food packaging to stop food going off…
o In industry, nitrogen gas is used to make ammonia which we convert into fertilisers
Uses for oxygen?
o To help people breathe, in hospitals
o High-temperature welding
o Steel-making process

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3 Water treatment
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Uses of water?
o Industry as raw material, and coolant
o Washing, cleaning and drinking
Treatment techniques?
o Passing the untreated water through filter beds made of sand to remove solid
particles
o The addition of chlorine to sterilise the water by killing microbes
How can we test for pure water? By measuring its boiling point
Distillation is bad because? It is an expensive process because of the energy costs involved in
heating large volumes
What is desalination? When salts are removed from water to make it useful, common in
countries with few sources of natural fresh water where sea water is used…
Seawater undergoes distillation at reduced pressure to lower the boiling point therefore
saving energy and costs
Where is desalination used? Used in oil-rich nations in Middle East and on some islands with
no natural sources of water apart from occasional rainwater

Fluoride in water
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Fluoride protects your teeth from decay
In some places, fluoride is added to their water supply
Arguments for and against fluoridation:

For fluoridation of water
Some areas have had fluoridated water
for over 50 years… no ill effects (apart
from fluorosis)

Against fluoridation of water
Fluorosis is a condition caused when children take in too
much chloride
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Studies
have linked excess fluoride to weakening of bones and
bone cancer
30% reduction in cavities on teeth where Benefits of fluoridation are not significant
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4 Rusting
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What chemical reaction takes place when iron corrodes? An oxidation reaction… Iron gains
oxygen to form iron(III) oxide
What is needed for rusting? Oxygen and Water
Water then becomes loosely bonded to the iron(III) oxide and the result is hydrated iron(III)
oxide – which we call rust
Word Equation? Iron + Oxygen + Water -> Hydrated iron(III) oxide (rust)

Preventing rust
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BARRIER METHODS
o Painting/Coating with plastic (ideal for big and small structures, and can be
decorative)
o Oiling/Greasing (done when moving parts are involved, like on bike chains)
SACRIFICIAL METHOD
o What does this involve? This involved placing a more reactive metal with the iron…
the water and oxygen then react with this sacrificial metal instead of with the iron
o What is often used? Zinc as it is more reactive than the iron
o Galvanising is the word used to describe…? When iron or steel is coated with a
protective layer of zinc
When is sacrificial protection more likely to be used?
o Where the coating is more likely to be scratched like on wheelie bins
o In harsh conditions such as on oil rig legs or ship’s hulls









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2 Group 1 – the alkali metals


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Where can the alkali metals be found? In group 1
Examples of alkali metals? Lithium (Li), Sodium (Na), Potassium (K)
How are they stored? They are stored in oil to stop them reacting with oxygen in the air
Other properties? Very soft, can be cut with a knife
When cut what colour? Silvery, shiny surface when first cut, however this quickly goes dull
as the metal reacts with oxygen in the air and forms a layer of oxide on the surface

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Why are alkali metals so reactive? The atoms of alkali
metals have one electron in their outer shell; they need
to loose just one electron to get a stable (noble gas)
electron structure
When bonding, what do they always form? Positive
metal ions
Melting and boiling points? Relatively low temperatures
for metals… going down the group the melting and
boiling points get lower
Reactivity of alkali metals? Increases going down the
group because it becomes easier to lose the single
electron in the outer shell to form 1+ ions
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3 The transition elements




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Properties of transition metals? Transition metals have the properties of ‘typical’ metals
Actual properties?
o Good conductors of heat and electricity
o They’re very dense, strong and shiny
o Transition metals are much less reactive than Group 1 metals
o They’re denser, stronger and harder than Group 1 metals and have much higher
melting points
What do transition metals often have? More than one ion…
Examples?
o Iron (II) ions Fe2+ give green compounds
o and Iron (III) ions Fe3+ form red/brown compounds (RUST)
Transition elements and their compounds are also very important in industry as catalysts…
Example? Iron is the catalyst used in the Haber process in making ammonia

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F-,Cl-, Br-
What can we do with two halogens, one more reactive than
the other? The most reactive of the halogens would displace
a less reactive halogen from solution of its salts
For example…?
o Chlorine + Potassium bromide -> potassium chloride + bromine
o Cl2 (aq) + 2KBr (aq) -> 2KCl (aq) + Br2 (aq)

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Larger atoms gain electrons less easily going down a group…
Therefore halogens get less reactive moving down the periods


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They produce OH- ions (aq) when we add
them to water
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What is a base? Bases are substances with a pH greater than 7 that can neutralise acids
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Iron oxide and copper hydroxide
What is an acid? Acids are substances which produce H+ (aq) ions when we add them to
water
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2 Making salts from metals or insoluble bases
Acids + metals
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What is a salt? A salt is a compound formed when the hydrogen in an acid is wholly or
partially replaced by a metal or ammonium ions
One way of making salts? By reacting acids directly with metals
When is this only possible? The metal must be more reactive than hydrogen
Equation?
o Acid + metal -> a salt + hydrogen
o Hydrochloric acid + magnesium -> magnesium chloride + hydrogen
o 2HCl + Mg -> MgCl2 + H2
Metals can be arranged in order of reactivity from their reactions with acids

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Speed of reaction determined by? The rate at which bubbles of hydrogen are given off
Test for hydrogen? Hydrogen makes a “squeaky pop” with a lit splint
Name a metal that doesn’t react with acids? Copper


Acid + insoluble base
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Equation?
o Acid + base -> a salt + water
What is a name for this sort of reaction? A neutralisation reaction
What salts for when we use
o Hydrochloric acid (HCl)? Always chlorides (containing Cl- ions)
o Sulfuric acid (H2SO4)? Always sulphates (containing SO42- ions)
o Nitric acid (HNO3)? Always nitrates (containing No3- ions)
Example of an acid + base reaction?
o 6HCl(aq) + Fe2O3(s) -> 2FeCl3(aq) + 3H2O (l)
o Hydrochloric acid + solid iron(III) oxide -> iron(III) chloride solution + water

Making a copper salt
Using copper (II) oxide (an insoluble base) and sulphuric acid, we can make copper sulphate crystals
Acid + base -> a salt + water
H2SO4 + CuO -> CuSO4 + H2O
Sulphuric acid + copper (II) oxide -> copper (II) sulphate + water
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Warm gently on a tripod and gauze (do
not boil)
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Excess black copper oxide can be seen
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When the reaction is complete, filter the solution to remove excess copper oxide
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Stop heating
when you see the first crystals appear at the edge of the solution
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This will give you larger crystals
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4 Metal carbonates
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Products of a reaction between calcium carbonate and hydrochloric acid?
Calcium carbonate + Hydrochloric acid -> Calcium chloride + Water + Carbon dioxide
Explain the test for carbon dioxide…?
o Limewater is a solution of calcium hydroxide… it is alkaline
o Carbon dioxide is a weakly acidic gas… so it reacts with the limewater
o Tiny solid particles of insoluble calcium carbonate are formed as a precipitate
o This precipitate makes the limewater turn cloudy
Equation?
o Calcium hydroxide + Carbon dioxide -> Calcium carbonate + Water
(limewater)

(insoluble white precipitate)
Ca(OH)2 (aq) + CO2 (g) -> CaCO3 (s) + H2O (l)
What do metal carbonates form when heated? The metal oxide and carbon dioxide
Facts and uses of limestone?
o Contains mainly CaCO3
o Is quarried
o Building material
o Powdered and used to control acidity in the soil
o Manufacturing cement, glass and iron
o Producing calcium oxide (lime) when heated

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How does magnesium carbonate decompose?
o MgCO3(s) -> MgO (s) + CO2 (g)

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Measure a known volume of alkali into a conical flask using a volumetric pipette
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Now add a few drops of acid/base indicator to the solution in the flask, and swirl
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Before doing this, you should first wash the
burette with distilled water, and then with some of the acid
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Remember to swirl the flask
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Keep repeating step 4 until the indicator in the flask changes colour as this means the end
point has been reached
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Repeat the process at least 3 times, discard any anomalous results, then calculate an
average value… Alternatively repeat the titration until you get two consecutive identical
results
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Work out how many moles of the “known” substance you have…
Number of moles = concentration × volume (DIVIDE BY 1000!!)
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Then using this information, you can work out the
concentration of the unknown substance you have, the
units being mol/dm3


÷ Mr
Remember…

mol dm3 ⇋ g dm3

× Mr




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2 Displacement reactions
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What is the rule for displacement? A more reactive metal will displace a less reactive metal
from an aqueous solution of one of its salts
What’s this sort of reaction called? A displacement reaction
What is oxidation? Oxidation is the loss of electrons
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3 Extracting metals
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What is a metal ore?
o A metal ore is rock that contains enough of the metal to make it economic to extract
the metal
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The carbon removes the oxygen from
the metal oxide to form carbon dioxide
What is the name for removing oxygen from a compound? Chemical reduction
How are metals more reactive than carbon extracted from their ores?
o Electrolysis is used on the molten metal compound

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5 Recycling metals
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Mining and extracting metals takes lots of energy, most of which comes from burning fossil
fuels…
Why is burning fossil fuels bad? Fossil fuels are running out so it’s important to conserve
them
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Example? Recycling copper only takes 15% of the energy that’s needed to mine and
extract new copper
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Landfill takes up space and pollutes the surrounding
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6 Bonding in metals
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How are atoms in metals arranged? They are built layer upon layer in a regular pattern…
What can we call the structure of metals? That have giant structures
Where are the electrons?
o The outer electrons from each metal atom can easily move throughout the giant
structure, forming a ‘sea’ of free-moving delocalised electrons surrounding the
positively charged electrons
What is meant by delocalised electrons? They are electrons that are no longer linked with
any particular metal ion in the giant metallic structure therefore they are free to move
throughout the giant metallic lattice

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o They conduct heat because the free-moving delocalised electrons gain energy when
heated and can move around within the metal, spreading the energy through the
metal more quickly
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8 Useful metals
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Where can transition metals be found? In the central block in the periodic table
Example of a useful transition metal? COPPER
How and why is it used?
o It can be bent but is still hard enough for plumbers to use as water tanks or pipes
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o Copper conducts electricity and heat very well

Copper alloys
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How is bronze made? By mixing copper with tin
Properties of bronze? It’s tough and resistant to erosion
Use? To make ships propellers

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1% carbon, are easily pressed into shapes,
and used for things in mass production, like car bodies
o High carbon steels, with a relatively high carbon content, is very strong but brittle
o Stainless steels, containing a higher percentage of other metals, are used in cutlery
because they are strong and hard, but most importantly resistant to corrosion
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1 How fast?
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How can we work out the rate of a chemical reaction?
o Measure how quickly the reactants are used up as they make products
o Measure how quickly the products are made
Equation for average rate of reaction?
Average rate of reaction =
o Amount of reactant used or Amount of product formed / time

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o Particles must collide with a certain minimum amount of energy before they can
react
What is the name given for the minimum amount of energy particles must have?
o Activation energy
How can we increase the rate of reaction (in theory in terms of particles)?
o Increase the frequency of reacting particles colliding with each other
o Increase the energy they have when they collide
How does increasing the surface area of a solid increase the rate of chemical reaction?
o This increases the frequency of collisions between reacting particles

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o When particles collide more frequently, there are more chances for them to react
Explain why particles colliding with more energy will increase the rate of reaction
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Which factor has a greater effect?
o Particles colliding with more energy has a greater effect


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This uses an iron catalyst
Catalysts are very specific however
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Catalytic
converters convert carbon monoxide (which is toxic) into carbon dioxide, and nitrogen
oxides (which causes acid rain) into nitrogen and oxygen

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What is a mixture? A mixture contains two or more elements or
compounds that are not chemically combined together…
What sort of compounds is crude oil mainly made up of? Hydrocarbons – they contain only
hydrogen and carbon atoms
What are fractions? Fractions are hydrocarbons with similar boiling points separated from
crude oil
What is the process called that we use to separate crude oil? Distillation
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? ALKANES
What are alkanes? Alkanes are saturated hydrocarbons – they contain as many hydrogen
molecules as possible in their molecules… no more hydrogen atoms can be added
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2 Fractional distillation
Properties of hydrocarbons
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The shorter the molecules……
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3 Burning fuels
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What happens when hydrocarbon fuels are burnt in plenty of air? The carbon and hydrogen
in the fuel are completely oxidised
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? SULFER
What happens to the sulfer when a fossil fuel is burnt>
o It reacts with oxygen, forming sulfer dioxide which is a toxic, acidic gas
Why is this bad?
o Sulfer dioxide is bad for the environment as it causes acid rain, which damages trees
as well as killing animal life in lakes
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It absorbs energy
released as radiation from the surface of the Earth, and it is adding to effects of climate
change, which affects global temperatures
What happens when there is not enough oxygen inside an engine?
o Incomplete combustion happens, and carbon monoxide is also produced which is a
toxic gas
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They are
a renewable source of energy that could be used to replace some fossil fuels
Examples?
o Biodiesel which is made from oils extracted from plants
o Biogas which is generated from animal waste

Advantages of biodiesel and other biofuels
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Biodiesel is much less harmful to animals and plants if spilled than the diesel we get from
crude oil
Biodiesel burns much more cleanly, reducing the particles emitted
Crops used to make biodiesel absorb carbon dioxide gas as they grow, so biofuels from
plants are in theory ‘CO2 neutral’
What is meant by CO2 neutral’?
o The amount of carbon dioxide given off when it burns is balanced by the amount
absorbed as the plants it is made from grow
Why can’t it be claimed that all biofuels make zero contribution to CO2 emissions?
o The CO2 released at various stages of the biofuel process need to be taken into
consideration… for example CO2 is released when…
o Fertilising and harvesting the crops
o Extracting and processing the biofuel
o Transporting the plant material and biofuel

Disadvantages of biofuels
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If we start to rely on oil-producing crops to produce biofuels, farmers will turn land once
used for food crops to land for growing biofuel crops
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Equation?
o Glucose ----yeast-----> ethanol + carbon dioxide
o C6H12OH (l) ---------> 2C2H5OH (aq) + 2CO2 (g)

Hydrogen – a fuel for the future
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Why is hydrogen seen as the ‘fuel of the future’?
o It burns well with a clean flame
o Because there is no carbon in the fuel, there are no pollutants made when hydrogen
burns and no extra carbon dioxide is added to the air
There are problems to overcome however…?
o When mixed with air and ignited, it is explosive, and this presents safety concerns in
case of leaks, or accidents…
o Also vehicles normally run on liquid fuels but hydrogen is a gas, therefore it takes up
a much larger volume than liquid fuels, so storage becomes an issue

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It is a
thermal decomposition reaction that breaks down molecules by heating them
Why? So we can make them into more useful hydrocarbons like petrol for cars
What are the products? Cracking produces saturated hydrocarbons which are used as fuels
(alkanes) and unsaturated hydrocarbons (called alkenes)
What happens in cracking?
o The long-chain hydrocarbon is vaporised
EITHER…
o This vapour is passed over a powdered catalyst (normally aluminium oxide) at a
temperature of between 400 and 700 degrees
OR…

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o The vapour is mixed with steam and heated to high pressure
What are alkenes? They are molecules that contain at least one double bond between their
carbon atoms which means they are ‘unsaturated’ with hydrogen atoms
What is the test for an alkene? They will turn orange bromine water colourless
Examples of alkenes?
o 1) Ethene Formula: C2H4
o 2) Propene Formula: C3H6
General formula for alkenes?

CnH2n
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Describe another way apart from fermentation of making ethanol
o Ethene is produced from crude oil (by cracking)
o Ethene (C2H4) will react with steam (H2O) to make ethanol
o The reaction needs a temperature of 300 degrees and a pressure of 60-70
atmospheres
o Phosphoric acid is used as a catalyst

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Example?
o Ethene (C2H4) is the smallest unsaturated hydrocarbon molecule
o We can turn it into a polymer known as poly(ethane) or polythene
o Polythene is a really useful plastic as it is easy to shape, strong and transparent


How do monomers join together?
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What happens when alkene (unsaturated) molecules join together?
o The double bond between the carbon atoms in each molecule ‘open up
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3 The properties of polymers
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What two things do the properties of a polymer depend on?
o The monomers used to make it
o The conditions chosen to carry out the reason
What are the two types of poly(ethene)?
o High density (HD)
o Low density (LD)
How can LD poly(ethene) be made?
o Using very high pressures and a trace of oxygen, ethane forms LD poly(ethene)
o The polymer chains are randomly branched so they can’t pack closely together
o Hence its low density
How can HD poly(ethene) be made?
o Using a catalyst at 50 degrees, and slightly raised pressure, ethane forms HD
poly(ethene)
o This is made up of straighter poly(ethene) chains
o Because of this, they are able to pack more closely together, hence its higher density

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HD poly(ethene) is also stronger and has a higher softening temperature than LD
poly(ethene)


Thermosoftening and thermosetting polymers
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What will Thermosoftening polymers do?
o Thermosoftening polymers will soften or melt easily when heated because their
intermolecular forces are relatively weak
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Intermolecular forces are strong
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This is true for
all plastics… But the intermolecular forces in different plastics can be very different
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4 New and useful polymers
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New polymers are being developed all the time
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Examples…?
o New softer lining for dentures (false teeth)
o New packaging materials

Light-sensitive plasters
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To remove the plaster, the top layer is peeled away from the lower layer which stays stuck to
the skin
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Later after the wound is
healed, the polymer is designed to dissolve and is harmlessly absorbed into the body
We are now recycling more plastics and finding new uses for them

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Microorganisms in soil feed on the
starch which means the plastic gets broken down more quickly
o Types of polymer have been developed that are made from plant products



Disadvantages of biodegradable polymers

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Disadvantages?
o Farmers who sell their crops to be turned into fuel and plastics could cause higher
food prices
o The destruction of tropical forests to create more farmland will destroy wildlife
habitats and could affect climate change

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the molecules of the homologous series of alcohols all
contain the –OH group
First three members of the homologous series of alcohols?

Alcohol

Number of carbon

Structural

atoms

formula

Methanol 1

CH3OH

Ethanol

CH3CH2OH

2

Propanol 3







CH3CH2CH2OH

Displayed formula

Carboxylic acids
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Functional group of carboxylic acids? –COOH functional group
First three members of the homologous series of carboxylic acids?

Carboxylic

Number of C

Structural

acid

atoms

formula

Methanoic

1

HCOOH

2

Displayed formula

CH3COOH

acid

Ethanoic acid

Propanoic acid 3

CH3CH2COOH


Esters
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What are esters?
o Esters are chemicals with pleasant smells
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What functional group does esters always have in? –COO–

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Which property allows them to do this?
o They are flammable
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3 Carboxylic acids and esters
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Most well known carboxylic acid and it’s structure?
o ETHANOIC ACID


Main use for ethanoic acid? It is the main acid in vinegar
What do carboxylic acids form when dissolved in water?
o They form acidic solutions
What happens if a carboxylic acid is reacted with a metal carbonate? Products?
o A salt, water and carbon dioxide


Why are carboxylic acids called ‘weak acids?
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They are weak compared with strong acids like hydrochloric acid
Why does this happen?
o Acids must dissolve in water before they show their acidic properties…
o With strong acids like HCl, the HCl molecules all ionise in water;
HCl (aq) à H+(aq) + Cl- (aq)
o In weak acids, most of the molecules stay as they are, for example in ethanoic acid;
o CH3COOH (aq) <--------> CH3COO- (aq) + H+ (aq)
o

Ethanoic acid

water

ethanoate ions hydrogen ions

Making esters
•
•

•
•
•
•
•














What are esters
How can we make esters?
o By reacting carboxylic acids with alcohols, usually using a strong acid like sulfuric
acid as a catalyst
For example?
Ethanoic acid + ethanol <-----------> ethyl ethanoate + water
CH3COOH + C2H5OH <-----------> CH3COOC2H5 + H2O
General equation?
Carboxylic acid + alcohol <----strong acid catalyst-----> ester + water

12
...
This energy often heats up its surroundings…
What are endothermic reactions?
o Endothermic reactions take in energy from their surroundings, and cause a ‘drop’ in
temperature as they happen…

Exothermic reactions
•

•

•

Example of exothermic reaction?
o Burning fuels like methane (natural gas)
o Neutralisation reactions
What is enthalpy change?
o Enthalpy change is any temperature change between the reactants and the products
of the reaction
In exothermic reactions, what is the value of enthalpy?
o Always NEGATIVE

Endothermic reactions
•
•

•

Examples of endothermic reactions?
o Thermal decomposition reactions… eg decomposition of calcium carbonate
Decomposition of calcium carbonate?
o Calcium carbonate strongly heated…
o It forms calcium oxide and carbon dioxide
In endothermic reactions, what is the value of enthalpy?
o Always POSITIVE

12
...
When pressed, small
particles of metal are scraped off which start off the crystallisation
o To reuse you boil the pack so the crystals re-dissolve

Cooling down
•

Chemical cold packs usually contain?
o Ammonium nitrate and water
o When ammonium nitrate dissolves, it absorbs energy from its surroundings ,making
them colder…
o The ammonium nitrate and water are kept separate in the pack, and when squeezed
or struck the bag inside the water breaks, releasing the ammonium nitrate

12
...
This is
endothermic
What happens when we add water to anhydrous copper (II) sulfate?
o Hydrated copper (II) sulfate is formed
o The substance changes from white to blue
o In this direction, the reaction is exothermic
...
4 Comparing the energy released by fuels
•
•

Energy released = mass of water heated × SHC of water (4
...
5 Energy transfers in solutions
•

Basically use the equation above, then calculate the energy released PER MOLE

12
...
endothermic process – more energy is absorbed
When new bonds are formed…
...
7 Bond dissociation energy calculations
•

•





















What is bond dissociation energy?
o Bond dissociation energy is the amount of energy needed to break the bond
between two atoms
o Measured in…? kJ/mol
For bond dissociation energy calculations, add up the total values for bond dissociation using
a balanced equation
...
If it is
negative, it is an exothermic reaction
...
1 Chemical equilibrium


•
•
•

•

What happens in a reversible reaction?
o In a reversible reaction, the products can react to re-form the original reactants
As the concentration of products builds up…
o The rate at which they re-form reactants increases…
What eventually happens?
o Eventually, both forward and reverse reactions are going at the same rate, but in
opposite directions
...
We call this equilibrium
...


13
...


PRESSURE
If the forward reaction produces more
molecules of gas…
… an increase in pressure decreases the amount
of products formed
...


•
•



If the forward reaction produces fewer
molecules of gas…
… an increase in pressure increases the amount
of products formed
...


What happens if you increase pressure in reversible reactions with gases?
o Increasing the pressure favours the reaction that forms fewer molecules of gas
Changing the pressure affects the equilibrium only if there are different numbers of
molecules of gases on each side of the balanced equation

Energy and equilibrium

TEMPERATURE
If the forward reaction is exothermic…
…an increase in temperature decreases the
amount of products formed
...


•

If the forward reaction is endothermic
… an increase in temperature increases the
amount of products formed
...


What happens if you increase the temperature in reversible reactions with gases?
o The reaction that is endothermic (taking in energy) will be favoured



13
...
The product is ammonia
...


EQUATION FOR HABER PROCESS?




13
...


Disadvantages of high pressure?
o Very high pressures need lots of energy to compress the gases
...


The effect of a catalyst
•
•

What catalyst is used
o An iron catalyst is used to speed up the reaction
A catalyst speeds up the rate of both the forward and reverse reactions by the same amount

•




























Therefore?
o It does not affect the actual yield of ammonia, but it is just produced more quickly

14
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At the same time, the negative ions move to the anode (positive
electrode)
Why do ionic substances need to be liquefied before they are electrolyzed?
o Ionic substances do not conduct electricity when they are solid as their ions are in
fixed positions in their giant lattice
...
Unless they react in water to form ions

14
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4 Electrolysis of brine
•

•

What happens when we pass an electric current through brine (sodium chloride)?
o Chlorine gas is produced at the anode
o Hydrogen gas is produced at the cathode
o Sodium hydroxide solution is also formed
Equation?

Sodium chloride solution ----electrolysis--> hydrogen gas + chlorine gas + sodium hydroxide solution
At the anode (+):
•
•
•
•

Negative chloride ions (Cl-) are attracted to the positive electrode
Chlorine ions are oxidised as they lose electrons
Chlorine atoms bond together in pairs and are given off as chlorine gas (Cl2)
Half equation -> 2Cl- (aq) -> Cl2 (g) + 2e- OR 2Cl- (aq) - 2e- -> Cl2 (g)

At the cathode (-):
•
•

Na+ and H+ are both attracted to the negative electrode
In this case, because hydrogen is less reactive than sodium, hydrogen gas is given off

•
•
•

(WHEN TWO IONS ARE ATTRACTED TO AN ELECTRODE, THE LESS REACTIVE ELEMENT IS DISCHARGED)
Hydrogen ions are reduced as they each gain one electron
Hydrogen atoms bond together in pairs and are given off as hydrogen gas (H2)
+
Half equation -> 2H (aq) + 2e -> H2 (g)

The remaining solution
•

Why is the remaining solution, sodium hydroxide, alkaline?
+
-
+
o Brine contains Na and Cl (from salt) and H and OH (from water)
+
+
o The Cl and H ions are removed during electrolysis, leaving behind a solution containing Na
and OH ions… ie
...
Bleach is very good at killing bacteria

Using hydrogen
•

Why is hydrogen made by electrolysing brine useful?
o It is particularly pure, therefore very useful in the food industry eg
...
5 Electroplating
•
•

What is an electroplated object?
o An electroplated object is coated with a thin layer of metal by electrolysis
Why would we electroplate an object?
o Improve their appearance
o Protect their surface
o Use smaller amounts of precious metals

Nickel-plating experiment
•
•
•

Where is the object to be electroplated put? (copper)
o The object to be electroplated is made the cathode (negative electrode)
Where is the plating metal put? (nickel)
o The plating metal is made the anode (positive electrode)
What does the electrolyte contain? (nickel sulfate solution)
o The electrolyte contains ions of the plating metal

At the anode
...

•
•












Nickel ions (Ni2+) from the solution are reduced… half equation?
o Ni2+ (aq) + 2e- -> Ni (s)
They gain 2 electrons and the nickel atoms are deposited on the copper cathode

15
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2 Tests for negative ions
•
•

Test for a carbonate?
o Add dilute acid
...
3 Separating mixtures
•

•

What is a mixture?
o A mixture is made up of two or more elements or compounds which are not
chemically combined together
Differences between compounds and mixtures?

Compounds
Compounds have a fixed composition (the ratio
of elements present is always the same in any
particular compound)
...
separating salt and sand

Crystallisation (separates soluble solid from a solvent)
•

Example?
o With salt solution, need to get the sodium chloride from the solution in water
o Water is evaporated by heating in an evaporating dish on a water bath as this is
gentler than heating with a Bunsen burner
o Heating should be stopped when small crystals first appear around the edge of the
solution
o The rest of the water is then left to evaporate at room temperature as this will
ensure the biggest crystals

Distillation (unlike crystallisation, solvent is collected)
•

•
•

•
•

What happens?
o A solution is heated and boiled to evaporate the solvent
o The vapour given off is then cooled and condensed back into a liquid for collection
o The dissolved solids remain in heated flask
What is a miscible liquid?
o Miscible liquids dissolve in each other, and have different boiling points
Why is it difficult to get pure liquids from mixtures of liquids by simple distillation?
o Vapour is given off from liquids before they actually reach their boiling point,
especially when the liquids have similar boiling points
How can separation be aided?
o A fractionating column can be added
What is a fractionating column?
o Usually a tall glass column filled with glass beads, fitted on top of the flask being
heated

15
...

Describe how to carry out chromatography
o Capillary tube used to dab a spot of the solution on a pencil line near the bottom of
a sheet of absorbent chromatography paper
o Paper is placed in a solvent at the bottom
o The solvent is allowed to soak up the paper, running past the spots of solutions
o The more soluble the substance, the higher it will travel up the paper
What is Rf (retention factor)?
o Retention factor is a ratio, calculated by dividing the distance a spot travels up the
paper by the distance the solvent front travels
o Rf -> distance spot travels / distance solvent travels
How can Rf values be used?
o Rf values can be measured and matched against database to identify specific
substances

Instrumental methods
•

•

Advantages of modern instrumental techniques?
o They are highly accurate and sensitive
o They are quicker
o They enable very small samples to be analysed
o They often need fewer people to carry out the analysis
Disadvantages of modern instrumental techniques?
o Usually very expensive
o Takes special training to use
o Modern equipment often gives results that can only be interpreted by comparison
with data from known substances

15
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They have a longer retention time
...




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