This revision guide is designed to help you study for thechemistry part of the IGCSE Coordinated Science course.

The guide contains everything that the syllabus says youneed you need to know, and nothing extra.

The material that is only covered in the supplementarypart of the course (which can be ignored by corecandidates) is highlighted in dashed boxes:

Some very useful websites to help you further yourunderstanding include:

•http://www.docbrown.info/ - whilst not theprettiest site this contains a lot of very useful andnicely explained information.•http://www.bbc.co.uk/schools/gcsebitesize/science/ - well presented with many clear diagrams,animations and quizzes. Can occasionally lackdepth.•http://www.chemguide.co.uk/ - whilst mostlytargeted at A-Levels this site contains very detailed

CHEMISTRY REVISION GUIDEfor IGCSE Coordinated ScienceCHEMISTRY REVISION GUIDE

for IGCSE Coordinated Science

Whilst this guide is intended to help with your revision, itshould not be your only revision. It is intended as astarting point but only a starting point. You should makesure that you also read your text books and use theinternet to supplement your study in conjunction withyour syllabus document.

Whilst this guide does contain the entire syllabus, it justhas the bare minimum and is not in itself sufficient forthose candidates aiming for the highest grades. If that isyou, you should make sure you read around a range ofsources to get a deeper knowledge and understanding.

targeted at A-Levels this site contains very detailedinformation suitable for those looking to deepentheir knowledge and hit the highest grades.

Finally, remember revision is not just reading but shouldbe an active process and could involve:

•Making notes•Condensing class notes•Drawing Mind-maps•Practicing past exam questions•Making flashcards

The golden rule is that what makes you think makes youlearn.

Happy studying, Mr Field.

C1: THE ELEMENTS OF CHEMISTRY

Atom: The smallest particle of matter

An atom: Some atoms:

Molecule: A small particle made from more than one atom bonded together

Molecules of an element:

Molecules of a compound:

Element: A substance made of only one type of atom

A solid element: A gaseous element:

Compound: A substance made from two or more

A solid compound A gaseous compound:

CHEMICAL FORMULASFormulas tell you the atoms that make up a compound

Eg 1. H2O – two H, one OEg 2. C2H6O – two C, six H, one OEg 3. Mg(OH)2 – one Mg, two

O, two H*Eg 4. CH2(CH3)2 – three C, 8 H*

*In this case everything in brackets is doubled

CHEMICAL EQUATIONS•Show the reactants you start with and the products you make•Must contain an arrow (!) NOT an equals sign (=)•Must be balanced – same number of atoms on each side

Eg. CH4 + O2 ! CO2 + H2OThis is unbalanced as there are 4 ‘H’ on the left but only 2 ‘H’ on the right. This must be corrected by adding a ‘2’ in front of the ‘H2O’:

CH4+ O2 ! CO2 +2H2ONow the H balances but there 4 O on the right and only 2 on the left. This must be balance by placing a ‘2’ in front of the ‘O2’

CH4 + 2O2 ! CO2 + 2H2ONow there is 1 ‘C’, 4 ‘H’ and 4 ‘O’ on each side so it balances.

MOLES AND MOLAR MASS•A ‘mole’ is the name we give to the number 6.02x1023 – it is used to talk about the numbers of particles involved in chemical reactions.•It is the number of atoms such that one mole has the same mass in grams as an atom’s atomic mass.

•Eg 1: Carbon has an atomic mass of 12.0, so a mole of carbon has a mass of 12.0g•Eg 2: Iron has an atomic mass of 55.8, so

masses of the elements in its formula:

•Eg 1: C2H6O (C=12.0, H=1.0, O=16.0) Molar mass = 12.0 x 2 + 1.0 x 6 + 16.0 x 1 = 46.0gThe number of moles of a substance present in a given mass is given by:

Moles = mass usedmolar mass

Eg: How many moles of ethanol (C2H6O) are

Solids, Liquids and Gases

from two or more different elements bonded together

Mixture: A substance made from two or more elements or compounds mixed but not joined

A mixture of compounds and elements:

•Eg 2: Iron has an atomic mass of 55.8, so a mole of iron has a mass of 55.8g

•The molar mass of a compound is the sum of the

Eg: How many moles of ethanol (C2H6O) are present in 69.0 g?

Moles = mass used = 69.0 = 1.5 molmolar mass 46.0

MOLE CALCULATIONSWhat mass of carbon dioxide (the unknown) is needed to produce when 50g iron (the known) oxide is reduced to iron.•Balanced Equation: 2Fe2O3 + 3C ! 4Fe + 3CO2

•Moles of Known (Fe2O3)= mass / molar mass = 50.0 / (55.8 x 2 + 16.0 x 3) = 0.313

•Moles of Unknown (CO2) = (moles of known /knowns) x unknowns= (0.313 / 2) x 3 = 0.470 mol

•Mass of Unknown (CO2) = moles x molar mass= 0.470 x (12.0 x 1 + 16.0 x 2) = 20.7g

COMBINING POWERSThis is the number of ‘bonds’ an element formsThe combining power is given by the periodic table.

•Groups I and VII form 1 bond•Groups II and VI form 2 bonds•Groups III and V from 3 bonds•Group IV forms 4 bonds•Group VIII forms 0 bonds

•Eg: NH3 – N (Gp V) has three bonds to Hs, each of the three Hs (Gp I) has one bond to N.

ATOMIC STRUCTUREAtoms are made of:Protons: mass = 1, charge = +1Neutrons: mass = 1, charge = 0Electrons: mass = 0, charge = -1

In a square on the periodic table the smaller number, the proton number gives the number of protons or electrons and the bigger number, the nucleon number the number of protons and neutrons together.

Eg 1: Boron has 5 protons, 6 neutrons, 5 electrons

Eg 2: Phosphorus has 15 protons, 16 neutrons 15 electrons

C2: CLASSIFYING THE ELEMENTS

Structure of the Periodic Table (PT on last page!)Elements arranged in order of increasing proton number.PERIODS:•The rows in the periodic table. •For example lithium, carbon and chlorine are all in period 2.GROUPS:•The columns in the periodic table.•Use roman numbers: I, II, III, IV, V, VI, VII, VIII•For example, F, Cl, Br, I are all in Group VII (the halogens) •Elements in the same group have similar properties and react in similar ways.•Eg. The halogens all react in the same way with sodium to form sodium fluoride (NaF), sodium chloride (NaCl) and sodium bromide (NaBr)

Periodic PatternsAcross a each period (row) you see the same patterns repeated. For example in each period:

•The size of atoms decreases from Group I to Group VIII•The number of electrons in the outer-shell increase by one as

Non-metals

Transition Metals

Group V

III: Noble G

ases

Group I: A

lkali Metals

Group II: A

lkali-Earth

Lanthanides and Actinides (metals)

Other Metals

H

MET

ALS

Conduct electricity, conduct heat, higher density, malleable

NO

N-

MET

ALS

Insulate electricity, insulate heat,lower density, brittle

Group V

II: Halogens

Group I: The Alkali Metals (Li, Na, K ...)

OxidesFormed when an element reacts with oxygen for example: lithium oxide (Li2O), calcium oxide (CaO), carbon dioxide (CO2), sulphur trioxide (SO3)

ACIDIC OXIDES •The number of electrons in the outer-shell increase by one as you move across each group•The melting point increases from Group I to Group IV and then decreases from Group IV to Group VIII

Group I: The Alkali Metals (Li, Na, K ...)As you go down Group I, the alkali metals get:

•More reactive•More dense•Harder•Higher melting point

The alkali metals react with water in the same way:Metal + water ! metal hydroxide + hydrogen

2Li + 2H2O ! 2LiOH + H2

The metal hydroxide is an alkali – it makes a pH greater than 7 when it dissolves in water (hence the name alkali metals)Lithium is high in Group I so reacts much more slowly thanpotassium which is lower in the group.

ACIDIC OXIDESMany non-metal oxides dissolve in water to make acids: carbon dioxide makes carbonic acid, sulphur trioxide makes sulphuric acid

BASIC OXIDESSome metal oxides are bases(such as CaO): they neutralise acids. Those that also dissolve in water are called alkalis (such as Na2O).

Group VII: The Halogens (F, Cl, Br, I)As you go down Group VII, the halogens get:•Less reactive•More dense•Higher melting point (F/Cl – gases, Br – liquid, I – solid)•Darker coloured (pale green! dark brown)Chlorine was used as a weapon because it’s very reactive, fluorine is so reactive it corrodes the bottles it is stored in!

The ChallengeYou need to be able to use an element’s position in the periodic table to predict its properties. This means being familiar with the properties of groups I, II, VII and VIII and understanding them in depth.

You may wish to research groups III, IV and VI in more detail using textbooks or the internet)

Group III (B, Al.....)Does not follow simple patterns – B and Al react in very different ways.

The oxide of aluminium (Al2O3) is amphoteric – this means sometimes it acts like an acid and sometimes like a base.

Group IV (C, Si, Ge...)Carbon exists in different forms (allotropes) – diamond, graphite, Buckminster fullerene, nanotubes.

Si and Ge are semiconductors –sometimes they conduct electricity and sometimes not.

Group VI (O, S, Se...)Main interesting point is the oxides of sulphur: sulphur dioxide (SO2) and sulphur trioxide (SO3) both exist and dissolve to form sulphurous- (H2SO3) and sulphuric-(H2SO4) acids respectively.

C3: PETROCHEMICALS –Refining Crude Oil

HydrocarbonsHydrocarbons are compounds of hydrogen and carbon only. The carbons are linked together with hydrogen atoms attached to them. They carbons can be arranged in straight chains (1), branched chains (2) or even rings (3).

Refining Oil – Fractional DistillationOil is a mixture of hundreds of hydrocarbons. This mixture has to be separated into its useful components using fractional distillation. Very hot crude oil is pumped into the fractionating columnwhere the hydrocarbons separate out by their boiling points, rising through the column until they get cold enough to condense. The compounds that condense at a particular temperature are called a FRACTION.

1

23

fuel gas, 1-4 carbons

petrol, 5-9 carbons

naptha, 6-11 carbons

kerosene, 11-18 carbons

diesel, 15-21 carbons

COOLERBubble Caps: the gaseous fractions bubble up through these until they get cool enough when they then condense.

ALKANESThe simplest hydrocarbons are the alkanes, they are saturated hydrocarbons which means they only contain single bonds. They are unreactive and make good fuels and solvents.

ALKENESThese are unsaturated which means they contain at least one double bond. They are very valuable as a starting point for making lots of other compounds....more on the next page!

As you move down the column, the fractions have longer carbon chains. This increases the attractive forces between molecules which leads to:

•Higher boiling points•Higher viscosity•Lower flammability

Fuel Gas – used for fuel, and to make other chemicalsNaptha – used mostly to make other useful compoundsKerosene – fuel for aeroplanesFuel oil – fuel for large shipsBitumen – used to surface roads

fuel oil, 20-27 carbons

Greases and wax, 25-30 carbons

bitumen, 35+ carbonsHOTTER

FORMULASMolecular formula: tells you all the atoms present in a molecule. Quick to write but little information.

Graphical formula: drawing showing how all the atoms in a molecule are connected – takes longer but tells you much more information.

C3: PETROCHEMICALS –Using the Products

EtheneThe gas ethene can be made into many other compounds so is too valuable to burn.

The double bond in ethene and other alkenes has a cloud of electrons around it which makes them very reactive. The reactions of alkenes involve adding things to the double bond

Reaction with SteamEthene reacts with steam in the presence of a phosphoric acid catalyst to make ethanol which can be used as a solvent or to make other useful compounds.

C2H4(g) + H2O(g) !!!! C2H5OH(g)

Testing for unsaturated hydrocarbonsWhen an orange solution of bromine is added to alkenes in the

CrackingBecause there is a greater need for hydrocarbons with shorter carbon chains we sometimes need to cut longer chains into shorter ones using the process of cracking.

A long alkane is heated, vaporised and passed over a ceramic catalyst produce a shorter alkane and an alkene.

Eg. 1: C8H18 ! C4H10 + C4H8

Eg. 2: C10H22 ! C7H16 + C3H6

Note:•The with the alkenes for each carbon there are 2 H (CnH2n); with the alkanes, for each C there are 2 H plus 2 extra (CnH2n+2).•Any combination of alkene and alkane can be made, including straight and branched chains, so long as the numbers of atoms balance.

Polymers (plastics)Polymers are very large molecules made from lots of smaller ones (monomers) joined together. Polymers can be many thousands of monomers long.

Addition Polymers – eg polythene, polystyrene, polyvinylchloride (PVC)These are formed by monomers containing a C=C double bond. The double bonds link together to form a continuous chain.

When an orange solution of bromine is added to alkenes in the presence of UV light, the bromine reacts with the double bond on the alkene to make a bromoalkane. The bromine water loses its colour so this makes it a good test for alkenes:

C2H4 + Br2 !!!! C2H4Br2

Homologous seriesThe alkenes are a homologous series, this means they are all similar (in this case containing a C=C double bond) but differ only in the length of their carbon chain. The alkanes are also a homologous series. The beginning of the name tells you the number of carbons and the end part the type of compound.

Condensation Polymers – eg nylon, polyester, KevlarThese are formed from monomers that contain a carboxylic acid group (-COOH) and either an –OH or an –NH2 group. The ‘acid‘ end of one monomer joins with the –OH/-NH2 of the other, spitting out water.

ThermoplasticsThe polymer chains are only weakly attracted to each other so these can be continuously melted and re-moulded. Easy to recycle.

ThermosetsThe polymer chains are joined with cross links, this means they decompose when heated instead of melting. Can’t be recycled (easily) or re-moulded.

polymer chains free to move when hot Cross-links prevent chains from moving

C4: CHEMICALS FROM PLANTS

CarbohydratesCarbohydrates are compounds of carbon, hydrogen and oxygen such as glucose, starch and cellulose.

Glucose:One of the most important carbohydrates (to humans) is glucose, C6H12O6. There are two important forms of glucose – alpha and beta. In alpha glucose (pictured) the OH circled in red points down, in beta glucose it points up; this seemingly small difference has big consequences.

Starch:Starch is a polymer made of thousands of alpha glucose units joined together. Plants use it to store energy and animals

Amino Acids and ProteinsProteins are polymers made of many amino acid monomers joined together

Amino Acids:Amino acids are compounds of carbon, hydrogen, oxygen, nitrogen (and sometimes sulphur) have the general structure shown left. The ‘NH2’ is the ‘amino’ part and the ‘COOH’ is the ‘acid’ part.

The ‘R’ means residue and can be any atom or group of atoms from something as simple as a hydrogen atom to something more complex like a benzene ring.

ProteinsProteins are long chains of amino acids whose properties are decided by the ‘R’ group on each amino acid. Proteins are condensation polymers forming water each time two amino acids join. Proteins are extremely important in biology – life could not exist without them.

Useful Natural Products:Cellulose, rubber and wood all have a wide range of uses. This is likely to increase in the future as they are renewable resources and we are more

Rubber:Rubber is a natural polymer with chains that are able to move past each other when stretched and then spring back. It has many uses including

joined together. Plants use it to store energy and animals (including humans) can easily digest it to get at that energy. Food such as bread, rice, noodles, pasta and potatoes contain a lot of starch.

Cellulose:Cellulose is a polymer made of many thousands of beta glucoseunits joined together. Plants use it to build their cell walls and give them strength. It can only be digested by bacteria and not animals.

Starch and cellulose are both condensation polymers – each time two glucoses join, one water molecule is produced.

Although they are very large molecules, the bonding in carbohydrates is just ordinary covalent bonding (see Unit C17).

Semi-permeable membranesSemi-permeable membranes are membranes with tiny holes in them. Small molecules such as glucose can move through these holes whereas large ones like starch can’t. The wall of our intestine is a semi-permeable so when we eat something containing starch – like rice – the starch molecules must first be digested into glucose molecules so they are small enough to be able to pass into our blood.

they are renewable resources and we are more aware of the need to live sustainably.

Cellulose:Comes from wood and has many uses, by far the most important of which is making paper and cardboard. The long fibres of cellulose are tangled into a fine, flexible web.

then spring back. It has many uses including making car tyres, rubber gloves and balloons.

Wood:Wood is strong, cheap and readily available and finds many uses especially for construction and furniture making.

!!!!""""Too big!!!

Starch

GlucoseSemi-permeable

membrane

C5: MATERIALS AND STRUCTURES

Properties of materialsMaterials can be described using words such as:•Strength – how much force it can resist?•Elasticity – how stretchy is it?•Hardness – how difficult is it to scratch?•Porosity – can air/water pass through it?•Transparency – does light pass through it?•Conductivity – does it conduct electricity or heat?•Biodegradability – does it break down naturally outside?

MoleculesA molecule is a small particle made from a few non-metal atoms bonded together – often fewer than 10 but sometimes much more (think polymers).

covalent bonds.

Molecular compounds have low melting points due to the weak intermolecular forces and do not conduct electricity as all electrons are stuck in

Ionic CompoundsMost compounds of a metal and a non-metal a made of ions – atoms that have gained or lost electrons. Usually the metal atom loses electrons to make a positive ion (cation) and the non-metal gains electrons to make negative ion (anion).

The positive and negative ions strongly attract each other – this is an ionic bond.

Giant Ionic StructuresIonic compounds don’t form molecules, they form crystals made of alternating positive and negative ions repeating millions of times in all directions. This is called a giant ionic lattice.

Properties of Ionic CompoundsWhen you melt or dissolve an ionic compound it conducts electricity because the ions are free to move towards the positive and negative electrodes. When solid the ions are stuck in position and there are no free electrons so they don’t conduct.

GlassGlass is made of silicon (IV) oxide - aka silica, SiO2 – with various metal oxides (such as sodium oxide or calcium oxide) added to it. The biggest source of silicon (IV) oxide is sand.

The metal ions cause the glass to have an amorphous giant polymers).

The atoms in a molecule are joined by strong covalent bonds. In a solid each molecule is held close to its neighbour by weak intermolecular forces. When a substance melts, it is these weak intermolecular forces that break NOT the strong

conduct electricity as all electrons are stuck in bonds and so unable to move.

Giant Covalent LatticesA crystal made of a repeating pattern of atoms joined with covalent bonds that repeats millions of times in all directions.

Examples include silica (SiO2) diamond (C) and graphite (C). They have high melting points because melting requires the breaking of strong covalent bonds. The don’t conduct electricity (except graphite) as there are no electrons free to move – they are stuck in bonds.

Graphite

Diamond

Silica

The metal ions cause the glass to have an amorphous giant structure, this is different to other giant structures because the atoms are disordered and do not form regular patterns.

Metal ions can be added to glass to give it colour for example:•Cobalt – blue•Iron (II) oxide – blue-green•Manganese – pale violet•Copper oxide – turquoise•Titanium – yellowish-brown

Recycling glass is beneficial for the environment as it uses less energy and resources. However it is hard to control the quality and consistency so is unsuitable for specialised applications.

Ceramics have a similar structure to glass and are made from clay that is fired at high temperature causing a chemical reaction that fuses its particles together.

C6: OXIDATION AND REDUCTION

Oxidation and Reduction

Oxidation is when something gains oxygen. Reduction is when something loses oxygen. Whenever one thing gets oxidised, another thing must get reduced (and vice versa).

2Fe2O3 + 4Al ! 2Al2O3 + 4Fe

In this reaction, the iron (in iron oxide) is reduced and the aluminium is oxidised (to aluminium oxide).

You can describe aluminium as a reducing agent because it reduces the iron. Reducing agents must be more reactive than the element they are reducing – in this case we had aluminium which is more reactive than iron.

Calculating % Metal ContentFactories processing ores need to know the percentage metal content so they know whether they can make enough money from it and how much metal to expect to produce.

% Metal Content = mass metal in ore x 100formula mass of ore

Eg. What percentage of iron is present in iron ore, Fe2O3? (Atomic masses: Fe=55.8, O = 16.0)% Iron = 2 x 55.8 x 100 = 69.9%

2 x 55.8 + 3 x 16.0

To calculate how much ore is needed to make a given amount of iron, divide the amount you want by the percentage (expressed as a decimal) Eg: To make 100 kg iron you need:Mass Iron needed = 100 = 143 kg

0.699

Reactivity Series Extracting Metals From Their Ores The limestone (CaCO ) reacts with impurities such as silicon to form

Extracting Minerals from the EnvironmentIn order to extract metals from their ores, we must first extract their ores from the earth. This can be done by open-cast mining (just dig a big hole) or shaft-mining (mining underground).

There are a number of issues associated with both processes:

•Dangerous – many workers killed each year•Polluting – can cause the release of heavy metals and other poisons into the environment•Habitat destruction – caused not just by the mine but all the roads etc needed to service it •Waste Disposal – vast mounds of spoil made.•Dusty•Increased heavy traffic•Noisy•Creates jobs – but can make an area over dependent on one income source•Ugly – destroys the natural beauty of places

Reactivity Series

MOST REACTIVE

Potassium, KSodium, NaCalcium, Ca

Magnesium, MgAluminium, Al

(Carbon, C)Zinc, ZnIron, FeTin, Sn

Lead, PbCopper, CuSilver, AgGold, Au

Platinum, Pt

LEAST REACTIVE

REA

CTIV

ITY

Extracting Metals From Their OresRocks that contain a significant amount of a metal are called ores. The metals in an ore are not present in their pure form but are bonded to other elements to form compounds – often oxides or sulphides. For example iron can be extracted from iron ore (Fe2O3, iron (III) oxide) and lead can be extracted from an ore called galena (PbS, lead sulphide).

Metals that are less reactive than carbon can be extracted by using carbon as a reducing agent (to steal the oxygen/sulphur). Metals that are more reactive than carbon must be produced by electrolysis.

Iron is less reactive than carbon so can be reduced by it. This is done in a blast furnace. Study the diagram then read the following:•Step 1: Carbon (coke) reacts with oxygen (from the hot air blast)

C (s)+ O2(g) ! CO2(g)•Step 2: Carbon dioxide reacts with more carbon to make carbon monoxide

CO2(g) + C(s) ! 2CO(g)

•Step 3: Carbon monoxide reduces the iron oxide (iron ore) to make molten liquid iron.

Fe2O3(s) + CO(g) ! Fe(l) + CO2(g)

The limestone (CaCO3) reacts with impurities such as silicon to form an easy-to-collect waste called slag (calcium silicate, CaSiO3):

CaCO3 +SiO2 ! CaSiO 3+ CO2

Step 1 happens here

Step 2 happens here

Step 3 happens here

C7: IONS AND ELECTROLYSIS

Products of Electrolysis

ElectrolysisElectrolysis is a process in which electricity is used to break compounds down into their elements. The mixture being electrolysed is called an electrolyte and must be liquid (either melted or dissolved) to allow the ions to move.

Cations (positive ions – remember they are ’puss-itive’) ions move to the cathode (the negative electrode) where they gain electrons, usually forming a metal.

Anions (negative ions) move to the anode (the positive electrode) where they lose electrons, usually forming a non-metal.

In the electrolysis of copper chloride (CuCl2)

(right) positive copper ions move to the cathodeand form copper metal. Negative chloride ionsmore to the anode and form chlorine gas.

Cu2+

Cu2+

Cu2+

Cu

Cu

CuCl- Cl-

Cl-Cl- Cl-

Cl-

Cl Cl

Cl Cl

Cathode (negative electrode)

Anode (positive

electrode)

Anions move to anode

Cations move to cathode

Layer of metal formed

Bubbles of gas formed

Molten Salt

Salt Solution

Cathode Metal

Metal, except with reactive metals (K, Na, Li Ca, Mg) in which case H2 gas is produced plus a solution of metal hydroxide

Anode Non-metalNon Metal, except sulphates in which case O2

Electrolysis of AluminiumAluminium can’t be extracted by reduction of aluminium oxide (Al2O3) using carbon as carbon is less reactive than aluminium. Instead

Molten aluminium oxide ( the electrolyte) is placed in a large carbon lined vessel which acts as the cathode. A large anode made of carbon is lowered into the electrolyte. The processes that

Purification of CopperWhen copper is made it contains lots of impurities. The copper is purified by electrolysis. A large lump of impure copper is is less reactive than aluminium. Instead

aluminium is produced by electrolysis.lowered into the electrolyte. The processes that take place are:

At the cathode:Aluminium ions gain electrons to make liquid aluminiumAl3+ + 3e- ! Al(l)

At the anode:Oxide ions lose electrons to make oxygen gasO2- ! ½ O2(g) + 2e-

The oxygen reacts with the carbon anode so it has to be replaced regularly

is purified by electrolysis. A large lump of impure copper is used as the anode, the electrolyte is copper sulphate solution and the cathode is made of pure copper.

At the anode, instead of anions losing electrons, neutral copper atoms lose electrons to become copper ions .

Cu(s) !!!! Cu2+(aq) + 2e-

These then move through the electrolyte to the cathode where they become copper atoms again.

Cu2+(aq) + 2e- !!!! Cu(s)

The anode loses mass as copper atoms leave it and the cathode gains mass as copper atoms join it. The impurities sink to the bottom as a pile of sludge.

Some TestsYou need to know two tests for elements that can be made during electrolysisChlorine gas – bleaches damp litmus paperOxygen – can relight a glowing wooden splint

The Electrolysis of Sodium Chloride (NaCl)The electrolysis of brine (sodium chloride solution) makes sodium hydroxide (many uses in industry), chlorine gas (used for many things including hydrochloric acid) and hydrogen gas (also used for many things including hydrochloric acid).

C8: SOLVENTS AND SOLUTIONS

SolutionsA solution is a mixture in which a solute is dissolved in a liquid solvent. When you dissolve something, it is still ‘there’ but it has been broken down into individual molecules or ions that are too small to see. If you added 10g of salt to 100g water, the solution will weigh 110g NOT 100g because the salt is still present, but just well mixed with the water.

Solubility and ConcentrationSome substances are more soluble in water than others, which means that more of the substance is able to dissolve. Sodium chloride is very soluble in water but silica (SiO2) is insoluble.

Generally ionic compounds, such as copper sulphate, dissolve in water whereas covalent compounds dissolve in non-aqueous solvents such as ethanol, acetone or hexane.

The ‘strength’ of a solution is called concentration. It is measured in units of ‘mol dm-3’ (pronounced ‘moles per decimetre cubed). 1.0 mol dm-3 means that 1.0 mole of solute is dissolved in 1.0 litres (dm3) of solution. In general:

Concentration = moles of solute .volume of solution in litres

Eg. 75.0g of glucose (C6H12O6) is dissolved in 250 cm3 of

water, what is the concentration of this solution?Moles of solute = mass used ÷ molar mass

= 75.0 ÷ (6 x 12.0 + 12 x 1.0 + 6 x 16.0) = 0.42 mol

Concentration = moles solute ÷ volume in litres= 0.42 ÷ (250 ÷ 1000*) = 1.68 mol dm-3

Some More TestsYou need to remember the chemical tests for the following ions:

Chloride ions:•Add acidified silver nitrate solution•See a white precipitate of insoluble silver chloride

•Cl-(aq) + AgNO3(aq) ! AgCl(s) + NO3-(aq)

Sulphate ions:•Add acidified barium nitrate solution•See a white precipitate of insoluble barium sulphate

•SO42-

(aq) + Ba(NO3)2(aq) ! BaSO4(s) + . 2NO3

-(aq)

Both these reactions rely on solid particles of an insoluble product being made, this precipitates out of the = 0.42 ÷ (250 ÷ 1000*) = 1.68 mol dm-3

*There are 1000 cm3 in 1 litre so this turns cm3 into litres

made, this precipitates out of the solution as ‘cloudy powder’.

Hard and Soft WaterHard water contains small amounts of dissolved calcium and magnesium minerals that can slowly form scale (deposits of calcium carbonate, magnesium hydroxide and calcium sulphate) which clogs pipes.

eg: Ca(HCO3)2(aq) ! CaCO3(s) + H2O(l) + CO2(g)

You can often tell water is hard by the behaviour of soap: in soft water it forms a bubbly lather and in hard water it leaves behind a grey scum. Softening water involves converting the minerals to insoluble compounds that settle out of the water.

Temporary hardness caused by magnesium- or calcium- hydrogen carbonate can be removed by boiling:

Mg(HCO3)2(aq) ! MgCO3(s) + H20(l) + CO2(g)

Permanent hardness caused by calcium sulphate can only be removed by sodium carbonate (washing soda):

CaSO4(aq) + Na2CO3(aq) ! CaCO3(s) + Na2SO4(aq)

Or by ion exchange. The water is passed through a column containing Na+ ions, these get swapped over with Ca2+ ions: Ca2+

(aq) + 2Na+(s) ! Ca2+

(s) + 2Na+(aq)

Drinking WaterWater drawn from rivers can contain pollutants such as fertilizers, dissolved organic matter, harmful bacteria and industrial waste that make it unfit to drink. At treatment plants, two main processes are used to make water safe:

Filtration – the water is passed through a series of increasingly fine filters that trap suspended particles. Activated carbon is used to filter out dissolved pollutants.Chlorination – chlorine is added to the water which destroys bacteria.

CleaningOften non-aqueous (not water) solvents are used in cleaning as they can dissolve the dirt, for example acetone can dissolve nail varnish.

Detergents are used to clean up oils and fats, for example in laundry powder or washing-up liquid.

Detergent molecules have two ends , one end dissolves in water and the other in oil which allows oil and water to mix

C9: ACIDS AND ALKALIS

Reactions of AcidsYou need to memorise these reactions, each one shows the general word equation then a specific example with symbols.

Acids and MetalsAcid + Metal ! Salt + Hydrogen•Hydrochloric acid + lithium ! lithium chloride + hydrogen• 2HCl(aq) + 2Li(s) ! 2LiCl(aq) + H2(g)

Acids and Base (like alkali but not always soluble)Acid + Base ! Salt + Water•Sulphuric acid + sodium hydroxide! sodium sulphate + water• H2SO4(aq) + NaOH(aq) ! Na2SO4(aq) + H2O(l)

Acids and CarbonatesAcid + Carbonate ! Salt + Water + Carbon Dioxide•Nitric acid + calcium carbonate! calcium nitrate + water +

What’s the salt?To work out which salt is formed during neutralisation reactions you need to know the ions formed by the acid or alkali when it dissolves.

Working out the name is easy, you just combine the name of the cation from the alkali with the anion from the acid.

For example potassium sulphate and sulphuric acid makes potassium sulphate.

Magnesium hydroxide and phosphoric acid makes magnesium phosphate

Working out the formula of the salt is a little more complicated, the key is to make sure the positive and negative charges on the cancel each other out to zero.

Substance Cation(s) Formed Anion(s) Formed

Hydrochloric acid, HCl 1 H+ Cl- , chloride

Nitric acid, HNO3 1 H+ NO3- , nitrate

Sulphuric acid, H2SO4 2H+ SO42- , sulphate

Phosphoric acid, H3PO4 3 H+ PO43- , phosphate

Sodium hydroxide, NaOH Na+ , sodium 1 OH-

Potassium hydroxide, KOH K+ , potassium 1 OH-

Magnesium hydroxide, Mg(OH)2 Mg2+ , magnesium 2 OH-

Ammonium hydroxide, NH4OH NH4+ , ammonium 1 OH-

Eg 1. Potassium nitrateK+ has one plus charge

Eg 2. Magnesium phosphateMg2+ has two plus charges•Nitric acid + calcium carbonate! calcium nitrate + water +

. carbon dioxide• HNO3(aq) + CaCO3(s) ! Ca(NO3)2(aq) + H2O(l) + CO2(g)

Neutralisation ReactionsAll acids form hydrogen ions (H+ ) when they dissolve, all alkalis form hydroxide ions (OH-). During neutralisation, the H+ and OH- react to form water:

H+(aq) + OH-

(aq) ! H2O(l)

This reaction is exothermic, which means it gives out heat and gets hot.

Finally, to write a balanced equation, you need to get the right number of waters, the simplest way is to remember that each ‘H+’ from an acid makes one water.

K+ has one plus chargeSO4

2- has two minus charges

You need two K+ to balance out one NO3

- so the formula is K2SO4

Mg2+ has two plus chargesPO4

3- has three minus charges

So you need three Mg2+ to balance out two PO4

3- so the formula is Mg3(PO4)2

Eg 1. Potassium hydroxide and sulphuric acidAs we have seen it makes K2SO4 which requires one H2SO4 and two KOH. Two H2O are made since the one H2SO4 produces two H+ ions

H2SO4 + 2KOH ! K2SO4 + 2H2O

Eg 2. Magnesium phosphateAs we have seen it makes Mg3(PO4)2 which requires two H3PO4 and three Mg(OH)2. Six H2O are made since each of the two H3PO4 produces three H+ ions.

2H3PO4 + 3Mg(OH)2 ! Mg3(PO4)2 + 6H20

The pH Scale•Acids have a pH of less than 7•Alkalis have a pH greater than 7•pH can be measured with colour changing indicators or digital pH meters

Some uses of BasesAntacids, used to cure indigestion, are basic salts – such as carbonates – that react with and neutralise acids.

Lime (calcium oxide, CaO) is used on a large scale to neutralise acidic industrial waste.

Testing CarbonatesTo test for carbonates, add a sample to some acid and bubble the gas collected through limewater. If the limewater goes cloudy, the sample contained a carbonate.

How much energy?Carry out a neutralisation reaction in an insulated container such as a polystyrene cup. By measuring the temperature change and the volumes you can work out how much heat was given out by the reaction (H = m.c.ΔT). You can then divide this by the number of moles of acid you had to work out how much energy one mole of acid produces.

C10: SOIL, ROCKS AND RATES

Rates of ReactionFor a chemical reaction to happen, the reacting particles need to collide with enough energy. Anything that increases the number of collisions or their energy will increase the rate.

TemperatureIncreasing temperature increases the rate of a reaction because particles are moving faster which means more collisions and higher energy collisions.

ConcentrationIncreasing the concentration of a solution increases the rate of a reaction because it means there are more particles available to react which leads to more collisions.

Surface Area/Particle sizeIncreasing the total surface area of

The Rock CycleThe rocks that make up the Earth’s surface are in a constant state of slow change that takes place on a timescale of millions of years. Igneous rocks are formed by magma from the mantle that comes out through volcanoes or moves to near the surface and cools before erupting. Sedimentary rocks are formed by small particles of rock that get eroded , transported and built up in a layer thick layer that squashes the particles at the bottom together forming new rock. Metamorphic rocks are formed when sedimentary rocks get hot enough to partially melt, changing their structure. This process of constant change is called the rock cycle.

Weathering Some Uses of Rockssurface area of particles (by using finer powder) increases the rate of a reaction because it means more particles at the surface are exposed to collisions.

How fast?On a graph showing the change in concentration of reactants or products, the gradient of the line tells you the reaction rate: steeper = faster,flat = stopped

WeatheringThis is the process whereby rocks are broken into ever smaller pieces by exposure to the environment. There are three classes of weathering:•Physical: for example water (the force of waves and rivers knocking bits off), exfoliation (caused by the day/night heating/cooling cycle leading to cracks that gradually expand over time) or freeze-thaw (water seeps into cracks, freezes, expands and enlarges the crack).•Chemical: for example hydrolysis (when rocks like feldspar react with acidic rainwater to form kaolin (china-clay)) or carbonation (naturally occurring carbonic acid in rain water (dissolved CO2) reacts with limestone to form soluble calcium hydrogen carbonate (Ca(HCO3)2))•Biological: the force of plants roots growing into cracks and forcing them apart.

Weathering releases nutrients present in the rocks and so is vital for making soils fertile.

Some Uses of RocksLimestone:•Used to remove impurities during iron production•Lime (CaO, produced by thermal decomposition of limestone) used to raise pH of acid soilsSand:•Used in glass production

Yet More TestsYou need to remember these chemical tests:•Oxygen (see Unit C7)•Hydrogen – lighting a test-tube of H2

with a splint gives a squeaky pop•Carbon dioxide – when bubbled through limewater it turns it cloudy.

C11: FERTILISERS

Ammonia, NH3The ammonia is alkaline gas – forming ammonium hydroxide (NH4OH) when it dissolves in water. Ammonia is very important since it is used to turn unreactive nitrogen gas (N2) into important nitrate (-NO2/3) containing compounds such as fertilisers and explosives, this is known as nitrogen fixation.

The Haber ProcessThis the process used to produce ammonia from nitrogen and hydrogen gases.

N2(g) + 3H2(g) ! 2NH3

The reaction is reversible which means some of the products turn back to reactants as soon as they are made, this means it

Sulphuric Acid, H2SO4

Sulphuric acid is another important chemical used in huge range of industrial processes. It is produced by the Contact Process. There are three chemical reactions. First sulphur is burnt in air to produce sulphur dioxide (SO2):

S + O2 ! SO2

Secondly SO2 is reacted with further oxygen to make sulphur trioxide (SO3):

2SO2 + O2 ! SO3This reaction is reversible, so to maximise the amount of SO3

made, they use a high temperature (425OC), medium-high pressure (1-2 times atmospheric pressure) and a catalyst (vanadium (V) oxide, V2O5). Finally, the sulphur trioxide is produced by first dissolving it in sulphuric acid to make oleum (H2S2O7) which then makes more sulphuric acid on the addition of water:

SO3 + H2SO4 ! H2S2O7

H2S2O7 + H2O ! 2H2SO4

FertilisersFertilisers are chemicals applied to plants to improve their growth and increase the amounts of products such as fruits, nuts, leaves, roots and flowers that they produce for us. They work by supplying plants with the vital elements they need including nitrogen - in the form or nitrate(NO3

- containing) salts, phosphorous – in the form of phosphate (PO4

3- containing) salts and potassium (K+ containing) salts.

Salts containing suitable ions can be prepared by reacting various combinations of potassium hydroxide, ammonia, nitric acid and phosphoric acid (see Unit C9).

Nitric Acid (HNO3)Nitric acid is prepared via a number of steps starting with the turn back to reactants as soon as they are made, this means it

takes a long time to make an economical amount of ammonia. To speed it up, the reaction is done at high temperature (~450OC), high pressure (~200 times atmospheric pressure) and with a catalyst (iron oxide).

oxidation of ammonia to nitric oxide (NO):4NH3 + 5O2 ! 4NO + 6H2O

This reaction is quite slow so a platinum catalyst is used to speed it up. Next, the nitric oxide is oxidised to nitrogen dioxide (NO2):

2NO + O2 ! 2NO2

Finally the nitrogen dioxide is reacted with water to produce nitric acid (HNO3):

3NO2 + H2O ! 2HNO3 + NO

More Tests....ayooohhhh!!You need to remember the following tests:•Ammonium ion (NH4

+) – add a few drops of cold sodium hydroxide. If ammonium is present it will produce ammonia which you can smell and the fumes will turn damp red litmus blue.•Nitrate ion (NO3

-) – boil the sample with sodium hydroxide and aluminium foil. If nitrate is present, ammonia will be produced so the fumes will turn damp red litmus blue

EutrophicationWhen it rains on fields that have been treated with nitrate fertilisers, they can dissolve in the rain water and be washed through the soil into streams, rivers and lakes. The nitrates then fertilise the growth of lots of algae in the water. When this dies, it sinks to the bottom and is rapidly decomposed by bacteria which use up most of the oxygen dissolved in the water, causing most fish and other aquatic life to suffocate. This process if called eutrophication and is a major problem.

This is not such a problem with phosphate salts since they are much less soluble so do not make it to the water in such large amounts and potassium on salts on their own can not cause such an effect.

Ammonia and AmmoniumAmmonia (NH3) is a gaseous compound the forms an alkali when it dissolves in water. The similarly named ammonium(NH4

+) is an ion formed when ammonia reacts with acids forming ammonium salts such as ammonium nitrate (NH4NO3) or ammonium sulphate ((NH4)2SO4).

C12: DYES AND DRUGS

DyesDyes are compounds used to colour fabrics.

Initially many dyes were produced from natural substances, for example ‘tyrian purple’ was produced from sea-snails, ‘red carthamine’ from safflowers and turmeric was used to dye things yellow. More recently, synthetic dyes have been invented, the first of which was the mauve coloured dye ‘mauvine’ invented by William Perkin in 1856. Synthetic dyes have replaced natural ones for most uses.

Substances called mordants are often added to help fix dyes to their fabrics. Before modern chemicals, one of the most widely used mordants was urine!

Melting/Boiling Point

The melting and boiling point of substance depend on how pure they are. For example Drugs

Paper ChromatographyPaper chromatography is a technique that can be used to separate mixtures of dyes or pigments such as chlorophyll. Firstly a very strong solution of the dye-mixture is prepared, this is then used to build up a small and intensely coloured spot on a piece of absorbent paper. This is then placed in a jar of solvent (with a lid). As the solvent soaks up the paper, it dissolves the coloured spot, causing it move up the paper as the solvent does. However because dyes have different levels of solubility, they move up the paper at different speeds causing the individual colours to separate out. The solvent or combination of solvents can be changed to get the best possible separation of spots.

PurityIt is important for chemists to be able to produce pure substances, this is especially the case for things like food additive or drugs that are used in depend on how pure they are. For example

water boils at 100OC but if you ‘pollute’ it with some salt, the melting point decreases to minus 3-4OC and can increase the boiling point to 103-4OC.

This effect is often used by chemists to judge the purity of the compounds they have made.

DrugsDrugs are chemicals that are used to change (generally to improve) physical or mental wellbeing. Many drugs have come from the study of plants, which is one of many reasons we should do all we can to protect the rainforests. Example include quinine used to treat malaria from the cinchona tree, vincristine from the rosy periwinkle flower used to treat childhood leukaemia and procaine from the coca plant used as a local anaesthetic.

Nb. You do not need to remember these

vincristine

procaine

quinine

AnalgesicsAnalgesics are drugs that relieve pain – better known as painkillers. Common examples include:

Aspirin

Paracetamol

things like food additive or drugs that are used in the human body. Whilst the drug or food additive itself may not be harmful to the body, there is no guarantee that any impurities won’t be. Because of this, chemists use a wide range of techniques including recrystallisation, chromatography and measuring the melting point to test the purity of their products.

Chemotherapy

Chemotherapy refers to taking specific drugs such as ‘cis-Platin’ that are designed to kill cancerous tumours. Most chemotherapy drugs generally target cells that divide rapidly – like cancer cells but also healthy cells like those found in bone marrow and the digestive tract. This means chemotherapy, whilst effective, takes a very heavy toll on the body.

C13: COLLOIDS

ColloidsA colloid is a mixture of one very fine particles of one phase of matter evenly spread throughout another. There are three major types of colloid:•Sol – fine particles of solid suspended in a liquid, for example blood (red blood cells suspended in water) or paint (pigment particles suspended in water)•Gel – small droplets of liquid trapped in a solid matrix, for example strawberry jelly (water trapped in solid gelatine)•Emulsion – fine droplets of one liquid suspended in another, for example mayonnaise (oil droplets suspended in vinegar) or milk (fat droplets suspended in water)

Diagram shows droplets of oil (blue) suspended in water

EmulsifiersAn emulsifier is a substance used to help make an emulsion by allowing the two liquids to mix without dissolving. For example you can’t make mayonnaise without egg yolk, the lecithin in the egg yolk is an emulsifier and allows the particles of oil to stay suspended in the vinegar. Without egg yolk the oil and vinegar would separate out straight away.

Emulsifiers work in a similar way to detergents. They are large molecules with one end able to dissolve in one type of substance and the other end able to dissolve in another type. So for example, in an oil/water emulsion, one end of the emulsifier can dissolve in water and the other in oil allowing small droplets of oil to be suspended in the water (or vice versa).

oil (blue) suspended in water(red) Colloids and Light

Colloids are always opaque (not transparent), light can’t travel through them.

The reason for this is that as photons of light hit the suspended particles they bounce off in a random direction rather than passing straight through, this is called scattering. You can see this effect when you bend a plastic ruler too much. Normally light passes straight through it but when you bend it just enough, you cause small areas of plastic molecules to rearrange themselves whilst others stay as they were. When light hits these areas it bounces off rather than passing straight through so the ruler appears white rather than transparent.

Longer (redder) wavelengths of light get scattered less than shorter (bluer) ones. This is what causes the colours of a sunset – the bluer colours of sunlight get scattered by dust suspended in the air whereas the redder colours are able to pass straight through.

This box is blank because there’s just not that much in this unit!

C14: FUELSCombustion (burning)In combustion, a fuel reacts with oxygen releasing heat. There are three requirements for fire, described by the fire-triangle. If the fuel is a hydrocarbon or carbohydrate the products of combustion are water and carbon dioxide (carbon monoxide if oxygen is limited).Fuel

A fuel is any substance that is burnt for the heat energy it releases. Good fuels need to have a number of properties, they must: burn easily, release a lot of heat on burning, burn without producing harmful products, be easy to handle and burn steadily (i.e. without exploding).

Solid fuels (such as wood and coal)Easy to handle and so safe to use but uses are limited by the inability to flow. Also tends to burn ‘dirtily’ producing the most pollution such as carbon dioxide, carbon monoxide and soot.

Finely powdered solid fuels can explode due to the high surface area causing an extremely high reaction rate (see unit C10)

Liquid fuels (such as oil, ethanol, petrol)Harder to handle as they flow (so they don’t stay in one place)

Fossil FuelsFossil fuels are formed from the remains of dead animals (oil and gas) and plant (coal) that collected over millions of years and were transformed by heat and pressure.

Most of the energy that human society uses comes from burning fossil fuels in power stations, factories and motor vehicles.

There are a number of problems with fossil fuels•They are running out quickly (especially oil)•They release carbon dioxide when burnt leading to global warming

Oxygen, O2

Oxygen gas has many uses:•Medicine – helps patients with impaired respiratory systems to breathe.•Welding – burns with ethyne gas to give a super hot flame.

Reducing PollutionIt is important to reduce the pollution and carbon dioxide that we produce. The only real way to do this is to burn fewer fossil fuels by:•Using less energy – by using less things that require energy such as computers and cars that require or using more energy efficient ones and avoiding energy waste (leaving lights on, using air-con with an open window etc.).•Using cleaner energy sources – renewable energy such as solar, wind and hydroelectric

In cars, the carbon monoxide (CO), nitrogen oxides (NO ) and unburnt hydrocarbons (HC) that but this makes them easy to store and to feed into engines.

Gas fuels(natural gas, methane)The hardest to handle and store requiring high pressure canisters. Flowing means they are well suited to use in engines and they also burn cleanly producing least pollution.

to global warming•The soot released when they burn damages wildlife and coats buildings in unsightly black

PollutionBurning fuels often produces pollution in the form of things like carbon monoxide, nitrogen oxides, un-burnt hydrocarbons and products of impurities such as lead and sulphur.

Carbon monoxide (CO)Formed when fuels burn in too little oxygen. Binds permanently to haemoglobin in your blood preventing your blood from carrying oxygen.

Lead (Pb)Highly toxic causing a wide range of symptoms, including affecting the brain development of children.

Acidic OxidesThe oxides of sulphur (SO2, SO3) and nitrogen (many including NO and NO2) are acidic which means when they dissolve in water they form acids. These gases are produced from burning fossil fuels, especially coal which is high in sulphur.

When these gases dissolve in the water in clouds they form acid rain which damages wildlife (by releasing toxic aluminium ions) and corrodes the stonework on buildings.

NO2 is also a key component in the formation of smog which is a major health risk in large cities.

oxides (NOX) and unburnt hydrocarbons (HC) that they produce can be converted to less harmful things with a catalytic converter.:

2CO + O2 ! 2CO2

2NOx ! N2 + xO2

2HC + 2O2 ! 2CO2 + H2OThe catalytic converter is part of a car’s exhaust pipe and uses a catalyst of platinum, rhodium or palladium to speed up these reactions.

Green MethaneMethane gas, a good fuel can be made from decomposing plant and animal waste (this is often called ‘biogas’). This makes fuel from a waste product so is environmentally better.

Hot WordsExothermic reactions get hotter (like burning fuels) whereas endothermic reactions get colder (for example dissolving salt).

C15: BATTERIES

Reactivity of Metals (check Unit The reactivity of metals can be seen by the way they react with steam or with acid (see Unit C6 for the reactivity series).

Reaction with water (see Unit C2 for details of this reaction):The most reactive metals (K-Ca) react with cold water, fairly reactive metals (Mg-Fe) will only react with steam whereas the least reactive metals (Sn-Pt) don’t react at all.

Reaction with dilute acids (see Unit C9 for details) The reaction of metals with acids shows a similar patter with the most reactive metals (K-Ca) reacting violently, the fairly reactive metals (Mg-Pb) reacting gradually more slowly and the least reactive metals (Cu-Pt) not reacting at all.

The reactivity of metals relates to how easily they form ions, more reactive metals like K form K+ ions much more easily

Voltaic CellsVoltaic cells produce electricity and comprise an electrolyte solution with electrodes made of two different metals dipping into it. The voltage of a cell can be changed by changing the metals used for the electrodes.

A chemical reaction takes place where the more reactive metal forms ions forcing ions of the less reactive metal to become atoms. This causes electrons to flow around the circuit from the more reactive metal to the less reactive metal. When one of the reactants (metal or electrolyte) runs out, the reactions stop so the cell no longer pro

The voltage of the cell is related to the position of the two metals on the reactivity series; the further apart they are the higher the voltage and the closer together they are the lower the

voltage. For example a cell using of potassium and platinum (furthest apart) would have a very high voltage, a cell using iron and tin (close together) would have a very low voltage.

V

Electrode(metal 1)

Electrolyte Solution

voltmeterElectrode(metal 2)

RustingRust (hydrated iron (III) oxide) affects most structures made of iron (or steel (see Unit C16)) and more reactive metals like K form K+ ions much more easily

than less reactive metals like Cu can form Cu+ ions.

Types of CellSimple Cells (Dry Cells): These are ‘normal’ batteries that can only be used once before they go flat. The reactions that generate the electricity are irreversible (they only go one way).

Rechargeable Cells: Like the batteries found in a your mobile phone or a car. The reactions are can be reversed when you put electricity back through the battery allowing you to charge it up.

Fuel Cells: Fuel cells ‘burn’ a continuous supply of hydrogen and oxygen to make electricity. The gases are separated by a special membrane that only lets hydrogen pass through it in the form of H+ ions. This means that when the H2 and O2 react, energy is released as electricity instead of heat.

Rust (hydrated iron (III) oxide) affects most structures made of iron (or steel (see Unit C16)) and causes huge damage:

Iron + oxygen + water !!!! hydrated iron (III) oxideRust can be prevented by taking steps making sure either oxygen or water can’t reach the iron. The main ways to do this involve covering the metal with, paint (bridges and other structures), oil/grease(moving machine parts) or another metal such as zinc (galvanising). Rust is also sometimes prevented by using sacrificial prevention where a more reactive metal (Mg, Zn) is used which corrodes in preference to the iron, this is often used to protect the hulls of ships.

When zinc and aluminium oxidise they form a waterproof layer of oxide that protects the metal from further damage. When iron rusts, the rust flakes off exposing more iron, this is why rust is so damaging.

Which Battery?Dry Cells:Dry Cells are cheap, convenient and can store a lot of energy but can only be used once and so are environmentally unfriendly. They last a long time, gradually giving lower and lower voltage.

Rechargeable Batteries:Can be used many times and the ones containing lithium are light. They are also expensive and older versions lose their ability to store energy after a number or recharges. They give the same voltage until they go flat.

Fuel Cells:Fuel cells run on a continuous supply of hydrogen and oxygen so don’t run out as such. They are very expensive and new technology and there is little infrastructure for producing and distributing hydrogen gas.

C16: METALS AND ALLOYS

Metals and their StructureMetals have a giant structure of atoms arranged in tightly packed rows in three dimensions.

Metals are joined together by metallic bonding in which metal ions are attracted to a ‘sea of electrons’ that surrounds them. This can happen because the outer-shell electrons of the metal atoms delocalise (meaning they are able to move around many atoms rather than just one) leaving

Some Commonly Used Metals and Alloys

Metal Properties

Iron Soft, magnetic, conducts electricity

Copper Easy to shape, ductile, excellent heat /electricalconductor

Aluminium Low density, strong resists corrosion

Titanium Low density, very strong, high melting point

Gold Shiny colour, very low reactivity, tarnish resistant

Alloy Metals Properties

Amalgam Mercury and Cu/Ag/Zn/Sn

Soft when formed, rapidly hardens – used for dental fillings

Brass Copper and Zinc

Malleable, soft, shiny golden colour, good conductivity – often used for decorative purposes on door handles

Solder Tin and Lead Good electrical conductor, very low melting point – used to join electrical components

Alloys With NumbersGiven the % of metal in a mass or alloy, the amount

Steel – a very useful alloyIron is too soft to have many uses, but when carbon (and sometimes a few other things) is added to make

Transition MetalsThese metals than just one) leaving

behind positive ions.

AlloysAlloys are ‘mixtures of metals’ (although sometimes they can contain a non-metal) that are made by mixing molten metals.

Alloys often have very different properties to the metals they are made from and by varying the metals they can be tailored to have specific desirable properties – this is called metallurgy.

Alloys are often harder than the metals they are made from. In a pure metal the rows of atoms are neatly lined up meaning they can slip past each easily when the metal is hit leaving a dent. Because alloys are made of atoms of different sizes, the atoms don’t line up neatly so can’t slip past each other so easily when hit.

Arrangement of atoms in an

alloy

Arrangement of atoms in a pure metal

mass or alloy, the amount can be found similar to with ores (see Unit C6).

(and sometimes a few other things) is added to make steel it becomes the most widely used metal of all.Mild Steel (~99.75% Fe, ~0.25% C): Strong, cheap and easy to shape – used in constructionHigh Carbon Steel (~99% Fe, ~1% C): Very strong but brittle – used to make toolsStainless Steel (80% Fe, 15% Cr, 4% Ni, 1% C): Corrosion resistant – Cr and Ni form waterproof oxide layer preventing further corrosionManganese Steel (84% Fe, 15% Mn, 1% C): Extremely hard – used for things like railways

The Last Tests!!!!Flame tests are used to indentify metals in compounds by the colour of flame they produce when burnt:Lithium - redSodium - yellowPotassium - lilacCalcium – orangey-redBarium – pale greenCopper – blue-green

Cu2+ – NaOH(aq) produces a blue precipitate which dissolves in NH3(aq)

Fe2+ - NaOH(aq) produces a dark green precipitate insoluble in NH3(aq)

Fe3+ - NaOH(aq) produces a brown precipitate insoluble in NH3(aq)

Zn2+ - NaOH(aq) forms a white precipitate soluble in NH3(aq)

These metals have high densities and boiling points and tend to form coloured compounds such as the bright blue copper (II) sulphate

C17: ATOMS, BONDING AND THE PERIODIC TABLE

Electron Arrangement/ConfigurationElectrons are arranged around atoms in specific shells. The most important shell is the outer one as this controls an atom’s chemistry. We call the electrons in the outer shell ‘valence electrons’ The number of electrons in the outer shell is the same an element’s group number.

The number of electrons around an atom is given by the atom’s proton number. They are arranged in shells as follows:

•1st Shell – Holds two electrons•2nd/3rd/4th Shells – Hold 8 electrons

•Example 1: Carbon. Proton number is 6 which means there are 6 electrons: 2 in the 1st shell and 4 in the second

•Example 2: Chlorine. Proton number is 17 which means there are 17 electrons: 2 in the 1st shell, 8 in the second and 7 in the 3rd.

Ionic BondingAn ionic bond is the attraction between two oppositely charged ions. Cations (positive) are formed when atoms (usually metals) lose electrons. Anions (negative) are formed when atoms (usually non-metals) gain electrons.

Atoms will lose or gain electrons until they have a complete outer shell: elements in Groups I, II and III will lose 1, 2 and 3 electrons respectively to form 1+, 2+ and 3+ ions. Atoms in Groups V, VI and VII gain 3, 2 and 1 electrons to form 3-, 2- and 1- ions. In an ionic compound the number of positive and negative and charges must cancel out to neutral.

Example: NaF, sodium in Group I forms a 1+ ion and fluorine in group VII forms a 1- ion so one Na+ is needed to balance out one F-

Example: Li2O, lithium in Group I forms a 1+ ion but oxygen in Group VI forms a 2- ion so two Li+

are needed to balance out one O2-

Li+O2-Li+Na+F-

Covalent BondingA covalent bond is the attraction of two atoms (usually non-metals)

Isotopes:Isotopes are atoms with the

Checking Your Answer: To check you are right, the period gives the number of shells and the group gives the number of electrons in the outer shell. For example chlorine is in Period 3 and Group VII so it has 3 shells and 7 electrons in the outer shell.

Ions: The configuration of ions is the same as for atoms but you have to take electrons away from positive ions and add extra for negative ions. For example oxygen and lithium.

and 7 in the 3 .

C

Cl

Li Li+O2-O

A covalent bond is the attraction of two atoms (usually non-metals) to a shared pair of electrons. Small groups of covalent bonded atoms can join together to form molecules.

The atoms share enough electrons to complete their outer shells.

*Nb: In bonding diagrams you only draw the outer shell and you use different shapes/colours to show where electrons have come from.

Example: H2O*, hydrogen is has one valence electron and needs one more to complete the 1st

shell, oxygen has six valence electrons electrons so needs two more. Thus one oxygen will react with two hydrogens:

Example: CO2*, carbon is has four valence electrons so needs four more to complete its outer shell, oxygen needs two more. Thus each carbon will react with two oxygens, sharing two electrons with each one. A bond involving two shared pairs is a double bond.

H HO

O OC

Isotopes are atoms with the same proton number but different nucleon number.

For example carbon has two main isotopes – C-12 and C-13. Carbon has a proton number of 6 so they both contain 6 protons and 6 electrons but C-12 has 6 neutrons and C-13 has 7.

A Noble MatterAtoms strive to have either 2 electrons (H, He) or 8 electrons (everything else) in their outer shells as this is very energetically stable –just like the Noble Gases. When bonding atoms gain and lose electrons to do this.