Chemstry AS

Unit 1 and 2

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  • Created on: 24-04-10 12:49

Atomic structure

Relative....mass....Relative charge

Proton .....1.......... -1+

Neutron.... -1......... 0

Electron.... 1/2000.. 1-

Isotopes are atoms of the same element with different number of neutrons

Atomic(proton) number is the number of protons in the nucleus of an atom

Mass(nucleon) number is the numbe of particles in a nucleus

An ion is a positively/negatively charged atom or group of atoms

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Atomic masses

Relative isitopic mass is the mass of a atom of an isotope compared with 1/12th of the mass of an atom of carbon-12

Relative atomic mass Ar is teh wieghted mean mass of an atom of an element compared with 1/12th of the mass of an atom of carbon-12

to find it: %of 1 type o element/100 x type number + (same as prev)

Relative molecual mass Mr is the wieghted mean mass of a molecule compared with 1/12th of the mass of the mass of an atom of carbon-12

Relative formula mass is the wieghted mean mass of a molecule of a formula unti compared with 1/12th of the mass of an atom of carbon-12

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Amount of substance and the mole

Amount of substance is the quantity whose unit is the mole. Its used as a mean of counting atoms.

To find amount of substance: n= m/M

Mass of 1 mole of atoms of any element as is the relative atomic mass in grams

The avagadro constant Na is the number of atoms per mole of the carbon-12 isotope(6.02x10^2 mol-1)

A mole is the amount of the substance containing as many particles as there are carbon atoms in exactly 12g of carbon-12 isotope

Molar mass M is the mass per mole of a substance. The units of molar mass are g mol-1. e.g Carbon = 12.0 g mol-1

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Types of formula

Emperical formula is the simplest whole number ratio of atoms of each element present in a compound

e.g 0.6075 g Mg combines with 3.995 g of Br

molar ratio: 0.6075/24.3; 3.995/79.9 = 0.025: 0.050

divide by smallest number= 1;2 = Mg Br2

A molecue is a small group of atms held togather by covalent bonds

The molecular formula is the actual number of atoms of each element in a molecule

e.g empirical form. mass of CH2 = 14

if Mr is 56 ; 56/14 =4 so molecular formula is C4H8

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Moles and gas volumes/solutions

Molar volume is the volume per mole of a gas. The units of molar volume are dm3 mol-1. At room temp.and pressure , the molar volume is aprox. 24.0dm3 mol-1.

To work out amountin moles in a sol: n=v(in dm3)/24 or n= v(in cm3)/24000

The concentration of a solution is the amount of solute in mol dissolved per 1 dm-3 of solution

Moles in solution: n=cxv (dm3) for cm3/1000

A Standard solution is solution of known concentration. there used in titrations to determine unknown information about another substance.

Concentrated sol= a large amount of solute per dm3

Dilute sol= A small amount of solute per dm3

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chemical equations and acids and bases

A species is any type of particles that takes place in a chemical reaction

An acid is a species that is a proton doner .e.g. H2SO4 (sulfuric acid), HCl, HNO3 (nitric acid, CH3COOH (ethanoic acid), HCOOH (methanoic acid), C6H8O7 (citric acid). When added to water they release protons (H+).

A base is a species that is a proton acceptor. e.g.metal oxides, metal hydroxides, ammonia (NH3), MgO, Ca(OH)2 calcium hydroxide. It accepts H+.

An alkali is a type of base that dissolves in water forming hydroxide ions OH-(aq) ions. e.g NaOH, KOH, NH3 (ammonia).

e.g NaOH(s) + aq > Na+(aq) + OH- (aq)

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A Salt is any chemical compound formed from an acid when a H+ ion from the acid has been replaced by a metal ion or another positive ion, usch as ammonium ion. NH4 +. e.g H2SO4= K2SO4

A cation is a positively charged ion.

An anion is a negatively charged ion.

Acid + carbonate = salt + CO2 + H2O

Acid + base = salt + water

Acid + alkali = Salt + water

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Water of crystallisation and titrations

Hydrated refers to a crystalline compound containing water moleculesAnhydrous refers to a substance that contains no water molecues.

Water of crystallistaion refers to water molecules that form an essential part of the crystalline structure of a compound.

To find water of crystallisation:1) mass of hydrated salt 2) mass of anhydrous salt 3) Mass of H2O 4) calculate mol of anyhydrous salt 5) calculate mol of water 5) determine forumla of hydrated salt by molar ratio anhdrous: H2O

Inidicator...... ...colour in acid...... colour in base........ end point colour

Methyl orange.. red..................... yellow

Bromothymol blue.. yellow

Phenolpthalin.... colourless............ pink................... pale pink

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Oxidation rumber

An oxidation number is a measure of the number of electrons that an atom uses to bond with atoms of another element. They are derived from a set of rules:

Species..................... Ox. No................ e,g

Uncombined element ..0 C,..................... Na, O2, P4

Combined O ..............-2 ..........................H2O, CaO

Combined H............... +1 .......................NH3, H2S

Simple ion ...............charge on ion ...........Na+ = 1+

Combined Fl.............. -1......................... NaF, CaF2

If iron (!!) cholride then is +2 on ion only

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Redox reactions

Oxidation is loss of electrons or an increase in oxidation number

Reduction is gain of electrons or a decrease in oxidation number.

A redoex reaction is where both oxidation and reduction take place.

A reducing agent is a reagent that reduces (adds e) antoher species

An oxidising agent is a reagent that oxidises (takes e) another species

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Evidence for shells

The first ionisation energyof an element is the energy required to remove 1 e from each atom in one molecule of gaseos atoms to form one mole of gaseous 1+ ions.

Factors affecting ionisation energy: atomic radius, nucleur charge,electron shielidng.

Electron shielding is teh repulsion between electrons in different inner shells. Shielding reduces the net attractive force from the positive nucleus on the outer shell electrons.

Succesive ionisation energies are a measure of the energy required to remove each electron in turn.

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Shells and orbitals

A shell is a groups of atomic orbitals with the same prinicpal quantum number n,

Principle quantam number n is the number represnting overall enrgy of each orbital which increases with distance from the nucleus. The set of orbitals with the same number n-value are reffered to as e shells or energy levels.

An atomic orbital is a region within a atom that can hold up to two electrons with opposite spins.

S orbital is spherical has 2 e in each shells.P orbital has 6 electrons ( shape 2 ovals is one p shell). D has 10 e and F orbital has 14 e.

To represent orbitals they always have opposite spins never same.

A sub-shell is a groups of same type fo atomic orbitals.Electron configuration is teh arrangement of e's in atoms

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Chemical bonding

The noble gases are the only unbonded atoms.

A compound is a substance formed form two or more chemically bonded elements in a fixed raio, shown by a chemical formula.

An ionic bond is teh electrostatic attraction between oppositey charged ions.

A giant ionic lattice is a 3 -dimensitonal structure of opp. charged ions held togather by strong ionic bonds.

A group is a vertical column in the periodic table.Elements in the same group have similar chemical properties and thier atoms have the same number of outer shell electrons.

Charges on common molecules NO3-, CO3 2-, SO4 2-, NH4+

A covalent bond is a bond formed by a shared pair of electrons

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continued..and shapes

A lone pair is an outer shell pair of electrons that is not involved in chemcial bonding.

A dative covalent or cooridnate bond is a shared pair of electrons which has been provided by one of the bonding atoms only.

Shape and bond angles:

Trigonal planer...120. (3 lines)

Tetrahedral......109.5...(4 lines-2 normal,1 wide, 1 lined)

Octahedral.......90......(6 lines- 2 normal, 2 wide, 2lined

A lone pair reduces bond angle by about 2.5...e.g Ammonia is pyrimadl (107) wiht one lone pair. Also linear shape due to double bonds, lone pairs can cause non-linear.

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Electronegativety and polarity

Electronegativity is a measure of the attraction of a bonded atom for the pair of electrons in a covalent bond.

A permenant dipole is a small charge differnce across a bond that results from a differnce in the electronegativateis of the bonded atoms.

A polar covalent bond has a permenent dipole.

A polar molecule has an overall dipole when you take into account any dipoles across the bonds.

Electronegativety increases across the periodic table.

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Intermolecular forces

Bond type................Relative strength


H bonds...................50

Dipole-dipole forces...10

VDV forces...............1

An intermolecular force is an attractive force between neighboring molecules.A permenent dipole-dipole force is a weak attractive force between permenent dipoles in neighboring polar molecules

VDV forces are attractive forces between induced dipoles in nieghboring molecules. the induced dipole is formed by instanatenous dipole in a whole molecule which is due to movement of electrons. As e increase VWV increase so boiling point increases.

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H bonding and mettalic bonding

H bonding is shown by a dotted line. Its found in molecules like O-H, N-H.

A hydrogen bond is a strong dipole-dipole attraction between: An e defecient H atom on one molecule and a lone pair of e's on a highly electronegative atom on a different molecule.

Ice is less dense then water as it has an open lattice with H bonds holding water molecules apart. When it melts the H bonds collapse causing water molecuels to move closer.

Mettalic bonding is a the electrostatic attraction between the + metal ions and delocalised e's. The delocalised e's are shared between more then 2 atoms.

A giant mettalic lattice is a 3 dimensional structure if + ions and deloclaised e's bonded togather by strong mettalic bonds.Properties of it are that they have high melting/boiling points, good electrical conductivity, malleability and ductility as delecolised electron allow layers to slide over each other.

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Properties of ionic/covalent bonds

Ionic compounds have high melting and boiling points has lots of energy is needed to breakt he strong electrostatic forces. They are good electric conductors if molten as ions are free to move then. They are soluble in polar solvents such as water.

A giant covalent lattice is a 3 demensional structure of atoms bonded togather by strong covalent bonds. They have high melting/boiling points, bad electrical conductors and are insoluble in polar/non polar solutions as lattice is strong.

A simple molcular lattice is a 3 dimensional stuctureof molecuels bonded togather by weak intermolecular forces. They have low melting/boiling point as force is weak VDW. They are non electrical conductors as no free particles and are souble in non polar colvents .e.g hexane

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Periodic table: ionisation energies, atomic radii

A period is a horizontal row of elements in the periodic table. A group is a vertical column in the periodic table. Elements in the same groups have same number of outer electrons.

Periodicity is a regular periodic variation of properties of elements with the atomic number and position in periodic table.

Ionisation across a period generally increases as no. of protons increase and e's are added to the same shell. So first ionisation energy increases across a period and the atomic radius also decreases.

Down a group the first ionisation energy decreases as the number of shells increase so shielding effect increases. The atomic radius increases down a group so the first ionisation energy decreases.

From group 1-4 boiling point increases(giant mettalic,mettalic bonding), group4-5 theres a sharp decrease(giant covalent,covalent bonding) and from group5-0 theres a low boiling point(simple molecular structure, VDW forces).

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Group 2

They have hydroxides that are alkaline so are called alkaline earth metals.

Have high melting/boiling points, light metals so low densities and form colourless compounds

They are oxidised in reactions.

They react vigourously with O forming xO

They react with water to form x(OH)2 + H2

There oxides/hydroxides are bases and neutrilise with acids to form salt and water. Oxides + water = metal hydroxides. Hydroxides dissolve in water to form alkaline solutions, the solubility increases down teh group so more alkaline solutions are formed.e.g Ca(OH)2 is used to neautrilise acid soils.

Group 2 carbonates decompose by heat forming metal oxide and CO2. It is called thermal decomposition.

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Group 7

They are more commonly known as halogens. They have low melting/boiling points and exist as diatomic molecules X2.

As you go down the group boiling points/VDW increases and a classic trend is shown of gas>liquid>solid.

They are the most reactive non metals. In redox reactions each halogen atom gains an e to form halide ion wiht -1 charge.e.g 1/2Cl2(g)+ e> Cl-(g)

They beccome less reactive down the group as ox.powers decerase also because atomic radius decreases, electron shielding decreases and the ability to gain e decreases.

Disproportion is the oxidation and reduction of the same element in a redox

Cl2 +H2O >HClO +HCl

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continued group 7

A displcement reaction is one in which a more reactive element displaces a less reactive one from an aqueous solution of the latters ions. If Cl oxidises Br its orange in H20/cyclohexane. If I then is brown in H2O and purple in cylcohexane. Br oxidises I and is brown in H2O and purple in cyclohexane.


Cl2...............pale green....pale green


To test for halides the unknown substance is dissolved in water then AgNO3(aq) is added. Ag+ (aq) react with any halide ion X-(aq) forming a perceptiate. If it is white= Cl, Cream= Br and Yellow=I

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Organic Chemistry

Hydrocarbons are organic compounds that contain C and H only.

A saturated hydrocarbon is a hydrocarbon with single bonds only.An unsaturated hydrocarbon contains C to C multiple bonds.

An aliphatic hydrocarbon is a hydrocarbon with C atoms joined togather in straight or branched chains.

An alicyclic hydrocarbon is a hydrocarbon with C atoms joined togather in a ring structure.

A functional group is the part of the organic molecule responsible for the chemical reactions.

A homologous series is a series of organic compounds with the same functional group but with each succesfull member differing by CH2

Alkanes are the homologous series with the general formula CnH2n+2

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Naming hydrocarbons

Nomenclature is a system of naming compounds.Asno of C increase the alkyl group becomes methy,ethyl,propyl,butyl,pentyl, hexyl, heptyl, octyl, nonyl,decyl.An alkyl group is an alkane with a H atom removed.

Type of compound........formula.......prefix.......suffix




Carboxylic acid.............COOH.........................oic acid

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A general formula is teh simplest algebric formula of a member of a homologous series.

A displayed formula shows the relative posistioning of all the atoms in a molecule and the bonds between them.

A structural formula shows the minimal detail for the arrangement of atoms in a molecule

A skeletal formula is a simplified organic formula with H atoms removed from the alkyl chains, leaving just a C skeleton and associated functional groups.

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Structural isomers are molecules with the same molecular formula but with different structural arrangements of atoms.e.g C4H10 can be Butane and 2 methylpropane

Stereoisomers are compounds with the same structural formula but with a different arrangements of the atoms in space.

E/Z isomerism is a type of stereoisomerism in which different groups attatched to each C of a C=C may be arranged differently in space because of the restricted rotation of teh c+c bond.

Cis-trans isomerism is a special type of E/Z isomerism in which there is a non-hydrogen group and hydrogen on each C of a C=C doouble bond. The cis isomer(Z) has the H atoms on each Carbon on the same side, the trans isoemr(E) has the H atoms on each carbon on different sides.

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Organic reagents and thier reactions

Homolytic fission is the breaking of a covalent bond, with one of teh bonded e going to each atom, forming two radicals.A radical is a species with an unpaired e. A single dot next to the species represents it.Heterolytic fission is the breaking of a covalent bond with both of the bonded e's going to one of the atoms, forming a cation and anion.

A nucleophile is an atom that is attracted to an e-defecient centre or atom, where it donates a pair of e to form a new covalent bond.An electrophile is an atom that is attracted to an e-rich centre or atom, where it accepts a pair of e to form a new covalent bond.

An addition reaction is a reaction in which a reactant is added to an unsaturated molecule to make a saturated molecule. 2 reactants>1 product

A subsitution reaction is a reaction in which a group of atoms/atom is replaced with a different atom/group. 2 reactants>2 product

An elimination reaction refers to the removal of a molecule form a saturated molecule to make an unsaturated molecule. 1 reactant> 2 Products

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Hydrocarbons from crude oil

Fractional distillation is the seperation of the components in a liquid mixture into fractions whihc differ in boiling pont by means of distillation typically using a fractional column.

Short chained hydrocarbons= low boiling point= top of column. Longer chained hydrocarbons are VV. Gases don't condense and pass at the outlet at the top as petroleum gas. The residue called bitumen is removed form the bottom of the column.

A branced alkane has a lower boiling point then an unbranced one as there are fewer points of contact between molecules so fewer VDW forces. If cahin lenght is bigger then boiling point increases as more points of contact.

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Hydrocarbons as fuels

Short chain aljanes burn in plentifull supply of O to form CO2 and H2O. e.g. CH4 (g) Methane + O2(g) > CO2(g) + 2H20(l)

Propane/butnae are easily liquefied and are known as LPG. The eq. for the combustion of octane is C8H18(l) + 12.5O2(g) > 8CO2(g) + 9H2O(l)

Soemtimes incomplete combustion takes place and forms CO .e.g.C8H18(l) + 8.5O2(g) > 8CO9(g) + 9H2O(l). CO is poisnous as it prevents heamoglobin form binding with O.

Cracking refers to the breaking down of long-chained saturated hydrocarbons to form a mixture of shorter chained alkanes and alkenes. There are many possible eq. for it.

A catalyst is a substance that increases the rate of a chemcial reaction without being used up in the process.

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Fossil fuels and fuels of the future

Crude oil : 90% of it is sued as a source of fuel. Plastics, pharmaceuticals, cosmetics, dyes and inks(petrochemicals) can also be made indirectly from it.

Most of the fuels produced are alkanes. Branched./cyclic are the best fuels. A good fuel has to be readily available, easily transported and inexpensive. A reason for scientists too look for new fuels is because these produce lots of pollutunts.e.g atomospheric pollutants: CO-Toxic gas from incombustion, CO2-Contributes too global warming via greenhouse effect, NO-Acid rain/destruction of forests and SO2-Acid rain.

Global warming is increasing the worlds average temperature. Main reason is human activity e.g. burning fuels. The greenhouse gases produced prevent heat form escaping the atmosphere. A warmer temperature causes change in climate, heavier rain, more violent storms, rise in sea levels and localised flooding.

Fuels fo te future are: biofuels-from recently living materiel plants/animal waste, agricultural crops-sugarcane/****, Ethanol-fermenting sugar or carbohydrates-blended with petroleum to burn effeciently-reduces harmful emissions, bioethonal and biodeisel-****seed blended with diesel.

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Subsitution reaction of alkanes

Alkanes react with halogens in presence of ultraviolet radiation or temp. of 300 .e.g CH4 + Cl2 > CH3Cl(chloromethane) +HCl. Its called radical subsitituion in which a readical replaces a different atom/group fo atoms.

Mechanism is a sequence of steps showing the path taken by e's in a reaction.

Mechanisation of Cl: 1) Initiaton(first step in radical subsitution in which free radicals are generated by ultraviolet radiation) Cl-Cl > Cl. + Cl. 2) Propogation(two repeated steps in a radical subsitution that build up the products in a chain reaction-is rapid/chain reaction): first step- CH4 + Cl. > .CH3 + HCl, second step- .CH3 + Cl2 > CH3Cl + Cl. 3) Termination( is the last step of a radical subsitution when two radicals combine to form a molecule): Cl. + Cl. > Cl2 / .CH3 + .CH3 > C2H6 / .CH3 + .Cl > CH3Cl

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Alkenes are usaturated hydrocarbons with at least on C=C bond. They have the general formula CnH2n. Are more reactive then alkanes and can form E/Z isomers.

A pi-bond is the reactive part of a double bond formed above and below the plane of the bonded atoms by sideways overlap of p-orbitals. It fixes the C in position.

A sigma bond is fomed directly above two carbon atoms vy the overlap of orbitals.

In alkens each C in double bond uses 3 e's in formation of sigma bond and 1 e's in formation of pi-bond.

Alkene molecule has a trigonal planer shape(120.)

Cyclic alkenes have a closed ring of C atoms contain 1 or more double bond .e.g cyclohexane.

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Reaction of alkenes

Are more reactive due to double bonds. As C-C bond enthalpy is +347 where as C=C bond has + 612. When an alkene reacts pi-bonds break but sigma bond remains intact.

They take part in addition reactions. a small molecule is added breaking the pi-bond.

Addition of H and gaseous alkane is passed over a catalyst of nickel at 150.C and an alkane is formed.

They react rapidly with halogens to give a di-subsituted halogenoalkane. The reaction is known as halogenation.

When Br is added to a sample with alkene in it the colour changes from orange too colourless. It shows it is has reacted with the double bond. It is used to test for unsaturation and checking presence of C=C double bond.

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Futher addition reactions of alkenes

When H halides adds across the double bond of an alkene it produces a halogenoalkane e.g. Ethene + HBr > Bromoethane.

Addition of steam is used to prepare alcohols, are heated at high temp./pressure in presence of a phosphoric acid catalyst. It is sometimes called hydration of alkenes. e.g. Ethene + Steam > Ethanol

Unsymmetrical alkenes take part in addition reactions forming organic products .e.g Propene > 2-bromopropane/1-bromopropane

Electrophillic addition is a type of addition reaction in which an elctrophile is attracted to an e-rich centre/atom, where it accepts a pair of e's to form a new covalent bond

Carbocation is an organic ion in which a C atom has a positive charge.

A curly arrow is a symbol used in reaction mechanisms to show the movement of an e pair in the breaking/formation of a covalent bond.

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Alkenes and Bromine

At room temp. producing a di-subsituted halogenoalkane. It is used as a test for unsaturation.

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Industrial importance of alkenes

Unsaturated compounds are important starting materiels for many industrial processes. Ethene is used to make: 1,2-dichloroethane-degreaser/paint remover, ethane-1,2-diol-antifreeze/polyesters, ethanoic acid-vinegar/organic synthesis.

A polymer is a long molecular chain made from monomer units.

A monomer is a small molecule that combines with many other monomers to form a polymer.

Addition polymerisation is the process in which unsaturated alkene molecuels add on to a growing polymer chain on at a time, to form a very long saturated molecular chain.

An addition polymer is a very long molecular chain, formed by repeated addition reactions of many unsaturated alkene molecules.

Radical polymeristaion-temp 200.c/leads to branching of polymer chain

The Zeiglar-Natta process-special catalysts e.g TiCl3 and Al(C2H5)2Cl/60'C

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Polymer chemistry/dealing with our waste

A repeat unit is a specific arrangement of atoms that occurs in the structure over and over again. Repeat units are included in brackets, outside of which is the symbol n.

Biodegradable materiel is a material that is broken down naturally in the enviroment by living organisms.

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Making and using alcohol

Ethanol can be made by two processes: the hydration of ethene and fermentation of sugars

Hydration fo ethene: made in presence of acid catalyst H3PO4/300'C/60 atm pressure- H2C=CH2(g) + H2O(g) > CH3CH2OH(l)- the reaction is reversible so conversion of ethene is incomplete.

Fermentation: Carbohydrates(sugar/starch) are converted into ethanol and CO2. It is done at low temp./presence of yeast/catalysed by an enzyme in yeast called zymase/25'C-37'C/anearobic. C6H12O6(aq) > 2CH3CH2OH(aq) + 2CO2(g)

Alcohol is sued for drinking, fuel, methylated spirits.

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Properties of using alcohol

Volatility is that ease that a liquid truns into a gas. Volatility increases as boiling point decerases. The presence of H bonds in alcohol results in alcohols having a lower volatility than alkanes of similar mass.

Alcohols dissolve in water because H bonds form between the polar -O-H groups of the alcohol and water molecules.

Solubility decreases as chain lenght increases: a larger part of alcohol molecule is made up of non-polar hydrocarbon chain and the hydrocarbon chain doesn't form any H bondds with water.

Primary alcohol is one in which -O-H group is attatched to a C atom with no alkyl groups or only bonded to one.e.g Methanol and Butan-1-ol

Secondary alcohol is in which the -oh group is attatched to C atom bonded with two alkyl groups e.g Propan-2-ol

Tertiary alcohol is in which a -O group is attatched to a C atom bonded to three alkyl groups .e.g. 2-methylbutan-2-ol

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combustion and oxidation of alcohols

In plentiful supply of O alcohols burn completely to form CO2 and H20. C2H5OH(l) + 3O2(g) > 2CO2(g) + 3H2O(l)

Primary and secondary alcohols can be oxidised using an ocidising agent e.g. acidified dichromate ions H+/Cr2O7^2- . It is made from pottasium dichromate K2Cr2O7 and sulphuric acid.

Primary alcohol : propan-1-ol + O > Propanol

Reflux is the continual boiling and condensing o a reaction mixture to ensure that teh reaction takes place wihtout the contents of the flask boiling dry.

Secondary alcohols: Butan-2-ol + O > Butanone

Tertiary alcohols are resistant to oxidation. The oxidising agent remains orange in colour.

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EStreifcation/dehydration of alcohols

Esterification is the reaction of an alcohol with a corboxylic acid to produce an ester and water. Acid catylst is concentrated sulfuric acid .e.g CH3CH2COOH (propanoic acid) + Ch3OH(Methanol) > CH3CH2COOCH3 (Methyl propanoate). In the reaction the OH bond is broken and water is frormed.

Esters are used as adhesives and solvents in chemical industry. the one resposible for the smell of orange is octyl ethanoate and pentyl ethanoate for banana.♥

Dehydration is an elimaination reaction in whihc water is removed form a saturated molecule to make an unsaturated molcule. In an elimaintion reaction 1 molecule > 2 moleucles

Alcohol can be dehydrated to form an alkene is the presence of an acid cataylst .

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They are compounds in which an H atom is replaced by at least one of the H atoms in an alkane chain.

They are used as refrigerants, aerosol propellents, degreasing agents and sry-cleaning solvents.

There general formula is CnH2n+1X, X is the halogen atom.

Reactivity: they containa polar C-X bond. Halogen atoms are more elctronegative so the bonded e pair is more attracted towards it. the reuslt is a polar bond. The electronegativity of halogens deceraeses down a group.

When halogenoalkanes react wiht an aq. solution of hot hydroxide ions the nucleophilic subsituion reaction takes place whihc produces an alcohol. Aqueos NaOH is mostly used in a reaction called hydrolysis. e.g. CH3CH2CH2Cl(aq) 1-chloropropane + OH-(aq) > CH3CH2CH2OH(aq) propan-1-ol + Cl-(aq)

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Reactions of halogenoalkanes

Nucleophilic subsitution is a type of subsitution reaction in whihc a nucleophile is attracted to an e defecient centre/atom, where it donates a pair of e to form a new covalent bond.

Rate of hydrolisis of different halogenoalkanes can be determined by : heating halogenoalkane with aq. silver nitrate with athanol added, water in the mixture acts a nucleophile. As hydrolysis takes place halide ions form. The aq silver nitrate reacts with any halide ions present forming a presepitate of teh silver halide. Rate is found by calculating time taken for precepitate to occur. Chloroalkane make s a white preceptite and for further one cream and yellow.

These affect hydrolysis: polarity- most polar so fastest reaction. Bond enthalpy- weakest bond gives fasted reactionn.

Hydrolysis rate increases downwards group 7.

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Halogenoalkanes and the enviroment/ % yield/atom e

Trouble of CFC's is that when they reach the stratosphere thye break down in the presence of ultravoilet radiation to form chlorine radicals whihc are thought to break down the ozone layer whihc allows harmfull uv rays to reach the lower atmosphere and increase chance of skin cancers. So the alternative are hydrofluorocarbons.

% yield= Actual amount in mol of product/ theoratical amount in mol of product x 100

A limiting reagent is the substance in a chemical reaction that runs out first.

Atom economy= Molecular mass of desired product/sum of molecular masses of all products x 100

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Mass spectrometry/reaction mechanisnms

Uses are: to identify unknown compounds, determine abundance of each isotope in an element, gain information about structure/ chemical properties of molecules.

The way its works:!) sample enters via the sample inlet 2) sample molecule is cooverted to ions by ionisation source 3)ions are propelled into a mass analyser 4) Ions are seperated according to there mass to charge ratio 5) Ions are detected.

Mass spectrometry is also used to determine the isoptopes present in an element. the mass charge ration is shown as m/z.

Molecular ion, M+ s the positive ion formed in mass spectrometry when a molecule loses an electron.

A radical is a species with an unpaired e-.

An electrohpile is an e pair acceptor. anucleophile is an e pair donor.

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Enthalpy/enthalpy profile diagrams

Enthalpy, H, is the heat content that is stored in a chemical system.

Exothermic refers to a reaction in whihc the enthalply of the products is smaller then the enthalpy of the reactants, resulting in heat loss to the surtroundings.(^H-ve) .e.g CH4(g) + 2O2(g) > CO2(g) + 2H2O(l) ^H=-890Kj mol-1

Endothermic refers to a reaction in whihc the enthalpy of the products is greater then the enthalpy of the reactants, resulting in heat being taken in from the surroundings.(^H+ve) .e.g CaCO3(s) > CaO(s) +CO2(g) ^H=+178Kj mol-1

An enthalpy profile diagram is a diagram for the reaction to compare the enthalpy of the reactants with the one of the products.

Actiavtion energy is the minimum energy required to start a reaction by the breaking of bonds.

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Standard enthalpy changes

Standard conditions are a pressure of 100 kPa a stated temperature, usually 25C and a concentration of 1 mol dm3.

Standard state is the physical state of a substance under the standard conditions of 100 k Pa and 25.

The standard enthalyp change of a reaction is the enthalpy change that accompanies a reaction in the molar quantites expressed in a chemical equation under standard conditions, all reactants and products being in their standard states.

The standard enthalpy change of combustion is the enthalpy change that takes place when 1 mole of a substance completely reacts with O under standard conditions, all reactants and products being in thier standard states.

The standard enthalpy change of formation of a compound is the enthalpy change that takes place when 1 mole of a compound is formed from its consituent elements in thier standard states under standard conditions.

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Determiantion of enthalpy chages/bond enthalpies

Specific heat capcity, c,.is the energy reqiored to raise the temperature of 1 g of a substane by 1 C.

Q(heat capacity)=mc^T

Bond enthalpy is the enthalpy change that takes place when breaking by homolytic fission 1 mol of a given bond in the molecules of a gaseous species.

Average bond enthalpy is the average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bong in the molecules of a gaseous species.

Hess' Law states that if a reaction can take place by more then 1 route and the initial and final conditions are the same then the total enthalpy change is the same for each route.

An enthalpy cycle is a diagram showing alternative routes between reactants and products which allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess' Law.

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Rates of reaction-collision theory/catalysts

The rate of reaction is the change in concentration of a reactant or a product in a given time.

Rate= change in concentration/time=mol dm3/s = mol dm-3s-1

Factors affecting it are : temperature, pressure, concentration, SA and catalyst.

Collision theory states that when two molecules collide a reaction might take palce if certain conditions are met and the molecules must have sufficeint energy to overcome the activation energy of the reaction and th molecules must also colide in the correct orientation.

Heterogenous catalysis is catalysis of a reaction in which teh catalyst has a differnt physical state form reactants. Homegenous catalysis are VV.

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Boltzmann distribution/chemical equilibrium

The Boltzmann distribution is the distribution of energies of molecules at a particular temperature,often shown as a graph.

Dynamic equilibrium is the equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction.

Le Chateller's principle states that when a system in dynamic equilibrium s subjected to a change, the position of equilibrium will shift to minimise the change.

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The greenhouse effect-global warming

It is not totally bad, it keeps the earths temperature constant. Earth recieves most of energy in form of electromagnetic radiation from the sun. The radiation passes throught the gases to the earths surface and some of the solar energy is absorbed and some released back to the amosphere as longer wave infrared radiation.

The greenhouse effect is the process in whihc the absorption and subsequent emission of infrared radiation by atmospheric gases warms the lower atmosphere and planets surfaces.

The gases: H2O vapour, CO2=volcanic erruptions/respiration/burning/decay,methane=prodution of fossil fuels,product of rotting waste,release from animals.

The gases e.g CO2 absorb infrared radiation causing the molecules to vibrate and some of the energy is released in the form of radiation which is then absorbed by another greenhouse gas or earths surface.

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The greenhouse effect-global warming

It is not totally bad, it keeps the earths temperature constant. Earth recieves most of energy in form of electromagnetic radiation from the sun. The radiation passes throught the gases to the earths surface and some of the solar energy is absorbed and some released back to the amosphere as longer wave infrared radiation.

The greenhouse effect is the process in whihc the absorption and subsequent emission of infrared radiation by atmospheric gases warms the lower atmosphere and planets surfaces.

The gases: H2O vapour, CO2=volcanic erruptions/respiration/burning/decay,methane=prodution of fossil fuels,product of rotting waste,release from animals.

The gases e.g CO2 absorb infrared radiation causing the molecules to vibrate and some of the energy is released in the form of radiation which is then absorbed by another greenhouse gas or earths surface.

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The ozone layer

Ozone=O3. It filters out shorter wavelenghts then ultravoilet raditaion which ould be very dangerous

Bad: Ozone near earths surfaces in trophosphere is an air pollutant with harmfull effects on repiratory systems.

Good; ozone is upper atmosphere in the stratosphere protects living organisms bypreventing harmfull ultraviolet light from reaching the eaths surfaces.

Formation: O2 + (radiation<240nm)= 2)..................O2 + O> O3 + heat

Removal of ozone: O3 + O > 2O2

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Ozone depletion

Ozone depletion potential ODP is the relative amount of breakdown to the ozone layer caused by the substance. It is compared with the ODP of trichloroflouromethane CFCl3.

Initiation stage:CFCl3 > Cl. + .CFCl2

Propogation step 1: Cl. + O3 > ClO. + O2

Propogation step 2: ClO. + O > Cl. + O2 so overall : O3 + O >2O2

For Nitrogen oxide NO. : P! ; .NO + O3 > .NO2 + O2 an P2; .NO2 + O > .NO + O2

so overall O3 + O > .2O2

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Controlling air pollution

Main pollutants: CO, Oxides of nitrogen, unburnt hydrocarbonsCO: poisonous gas emitted by incomplete combustion of hyrocarbons. It binds to heamoglobin so reducing O supplied to tissues. Poisoning symptoms are disurbed vision/tiredness.

NOx: fuel burned in presence of O when air is drawn into the cylinder with fuel forms it .e.g NO/NO2. It forms low level of ozone, contribues to acid rain=nitric acid, respiratory irritants.

Unburnt hydrocarbons: Volatile organic compounds are released in wehicle exhaust gases from unburnt fuels. Two are Benzene and Buta-1,3-diene are known as human carcinogens.Unburnt hydrocarbons and NO2 form low level ozone(energy provided by sunlight) leading to ozone formation involves radicals.

Oxidaitation catalysts: 2CO(g) + O2(g) > 2CO2(g)......C12H26(l) + 18.5O2(g) > 12CO2(g) + 13H2O(l).............2NO(g) + 2CO(g) > N2(g) + 2CO2(g)

Absorption is the process that occurs when a gas, liquid/solute is held to the surfce of S/l.

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Green Chemistry

Sustainability means the development of processes that prevent the depletion of natural resources.

This is done by using 12 principles: Prevention, Atom economy, less hazardous chemical synthesis, designing safer chemicals, safer solvents and auxilieries, design fo energy effeciency, use of renewable feedstocks, reduce deriatives, catalysis, desging for degradation, real time analyisis for pollution prevention and inherently safer chemistry.

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Relative mass of an electron is 1/1836 or 1/1840 not 1/2000.



Sorry to complain but there is MANY spelling mistakes!!!!



sorry about the spelling mistakes and ermmm about the reltaive atomic mass well i'm simply writing what the book says...Mayeb your specification is different.



This is really good :) I hope you do well in your exam



thankyou!! x



what board is this from?

thanksss x

Kazveen Aamer


thsi is extreamly helpful =) thank youu **



The board is OCR and thanks **



Is this ocr b salters? x

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