better hope – brighter future

Rutherford'sscatterin

gexpe

rimen

t

Abeamofalphaparticlesaredirectedataverythingoldfoil Mostofthealpha particles

passedrightthrough.Afew(+)alphaparticleswere

deflectedbythepositivenucleus.

Atinynumberofparticlesreflectedbackfromthe

nucleus.

AQAGCSEAtomicstructureandperiodictablepart1

Atom

s,

elem

entsand

compo

unds

Atom Thesmallestpartofanelementthatcanexist

Havearadiusofaround0.1nanometresandhavenocharge(0).

Element Containsonlyonetypeofatom

Around100differentelementseachoneisrepresentedbyasymbole.g.O,

Na,Br.

Compound Twoormoreelementschemicallycombined

Compoundscanonlybeseparatedintoelementsbychemicalreactions.

Method Description Example

Filtration Separatinganinsolublesolidfromaliquid

Togetsandfromamixtureofsand,saltandwater.

Crystallisation Toseparateasolidfromasolution

Toobtainpurecrystalsofsodiumchloridefromsaltwater.

Simpledistillation Toseparateasolventfromasolution Togetpurewater fromsaltwater.

Fractionaldistillation

Separatingamixtureofliquidseachwithdifferentboilingpoints

Toseparatethedifferentcompoundsincrudeoil.

ChromatographySeparatingsubstancesthatmove

atdifferentratesthroughamedium

Toseparateout thedyesinfoodcolouring.

Mixtures Twoormoreelementsorcompoundsnotchemicallycombinedtogether

Canbeseparatedbyphysicalprocesses.

Thedevelopmentofthemodeloftheatom

Pre1900 Tiny solidspheres thatcouldnotbedivided

Before thediscoveryoftheelectron, JohnDaltonsaidthe

solidspheremadeupthedifferentelements.

1897‘plum

pudding’

Aballofpositivechargewithnegativeelectrons

embeddedinit

JJThompson‘sexperimentsshowedthatshowedthatanatom

mustcontainsmallnegativecharges(discoveryofelectrons).

1909nuclearmodel

Positivelychargenucleusatthecentresurrounded

negativeelectrons

ErnestRutherford'salpha particlescatteringexperimentshowed

thatthemasswasconcentratedatthecentreoftheatom.

1913Bohrmodel

Electronsorbitthenucleusatspecificdistances

Niels Bohrproposedthatelectronsorbitedinfixedshells;thiswassupportedbyexperimental

observations.

+--

--

--

--

+-

- - -

-- -

JamesChadwick

Providedtheevidencetoshowtheexistenceofneutronswithinthenucleus

Chemicalequations

Showchemicalreactions- needreactant(s)andproduct(s)energyalwaysinvolvesandenergychange

Lawofconservationofmassstatesthetotalmassofproducts=the

totalmassofreactants.

Wordequations

Uses wordstoshowreactionreactantsà products

magnesium+oxygenàmagnesiumoxide

Doesnotshowwhatishappeningtotheatomsorthe

numberofatoms.

Symbolequations

Uses symbolstoshowreactionreactantsà products

2Mg+O2à 2MgO

Showsthenumberof atomsandmoleculesinthereaction,these

needtobebalanced.

Relativeelectricalchargesofsubatomicparticles

NameofParticle

RelativeCharge

RelativeMass

Proton +1 1

Neutron 0 1

Electron -1 Verysmall

7Li3

Massnumber

Thesumoftheprotonsandneutronsinthenucleus

Atomicnumber

Thenumberofprotonsintheatom

Numberofelectrons=numberofprotons

Relativ

eatom

icm

ass

Isotopes

Atomsofthesameelementwiththesamenumberofprotonsanddifferentnumbersofneutrons

35Cl(75%)and37Cl(25%)Relativeabundance=

(%isotope1xmassisotope1)+(%isotope2xmassisotope2)÷ 100

e.g.(25x37)+(75x35)÷ 100=35.5

Centralnucleus Containsprotonsandneutrons

Electronshells Containselectrons

Electron

ic

structures

Electronicshell

Max numberofelectrons

1 2

2 8

3 8

4 2

better hope – brighter future

AQAGCSEAtomicstructureandperiodictablepart2

Metalsandnonmetals

Developm

ent

ofth

ePerio

dic

table

ThePeriodictable

Group0

Grou

p1

Grou

p7

Transitionmetals(Chemistryonly)

H

Li

Na

K

Rb

Cs

Fr

Be

Sc Ti

Mg

V Cr Mn Fe Co Ni Cu Zn Ga Ge Se BrCa Kr

Y Zr Nb Mo Tc Ru Pd Ag Cd In Sn SbSr TeRh

Ba Hf Ta W Re Os Ir Au Hg Tl Pb Bi PoLa AtPt

Ra Rf Db Sg Bh Hs Mt ? ?Ac ?

Al P

N O

S Cl

F Ne

Ar

Rn

I

Si

Xe

He

B C

As

1 2 3 4 5 6 7 0Elementsarrangedin

orderofatomicnumber

Elementswithsimilarpropertiesareincolumns

calledgroups

Elementsinthesame grouphavethesamenumberofoutershellelectronsandelementsinthesameperiod(row)havethesamenumberofelectronshells.

Metalstotheleftofthisline,nonmetalstotheright

NoblegasesAlkalimetals Halogens

Transitionmetals

Beforediscovery

ofprotons,

neutronsand

electron

s

Elementsarrangedinorderofatomicweight

Earlyperiodictableswereincomplete,someelementswereplacedin

inappropriategroupsifthestrictorderatomicweightswasfollowed.

Men

deleev

Leftgapsforelements thathadn’tbeendiscoveredyet

Elements withpropertiespredictedbyMendeleevwerediscoveredandfilledinthegaps.Knowledgeofisotopes

explainedwhyorderbasedonatomicweightswasnotalwayscorrect.Metals

TotheleftofthePeriodic

table

Formpositiveions.Conductors, highmeltingand

boilingpoints,ductile,malleable.

Nonmetals

TotherightofthePeriodic

table

Formnegativeions.Insulators,lowmeltingandboilingpoints.

Nob

legases

Unreactive,donotformmolecules

This isduetohavingfulloutershells ofelectrons.

Boilingpointsincreasedownthegroup

Increasingatomicnumber.

Alkalimetals

Veryreactivewithoxygen,waterand

chlorine

Only haveoneelectronintheiroutershell.Form+1ions.

Reactivityincreasesdown thegroup

Negativeouterelectronisfurtherawayfromthepositivenucleussois

moreeasilylost.

Withoxygen

Formsa metaloxide

Metal +oxygenàmetaloxide

e.g.4Na +O2 à2Na2O

Withwater

Formsametalhydroxideand

hydrogen

Metal+wateràmetalhydroxide+

hydrogen

e.g.2Na+2H2Oà2NaOH+H2

Withchlorine

Formsametalchloride

Metal+chlorineàmetalchloride

e.g.2Na+Cl2 à2NaCl

Halogens

Consistofmoleculesmadeofapairofatoms

Havesevenelectronsintheiroutershell.Form-1ions.

Melting andboilingpointsincreasedownthegroup(gasà liquidà

solid)Increasingatomicmassnumber.

Reactivitydecreases downthegroup Increasingprotonnumbermeansanelectron ismoreeasilygained

With

metals

Formsa metalhalide

Metal +halogenà metalhalide

e.g.Sodium+chlorineàsodiumchloride

e.g.NaClmetalatomloses

outershellelectronsandhalogengainsanoutershellelectron

With

hydrog

en

Formsahydrogenhalide

Hydrogen +halogenàhydrogenhalide

e.g.Hydrogen+bromineà hydrogenbromide

e.g.Cl2 +H2 à 2HCl

With

aqu

eous

solutio

nofa

halid

esalt Amorereactive

halogenwilldisplacethelessreactivehalogenfromthesalt

Chlorine+potassiumbromideà potassiumchloride+bromine

e.g.Cl2 +2KBrà2KCl+Br2

Comparedtogroup1

• Less reactive• Harder• Denser

• Highermeltingpoints

• Cu2+isblue

• Ni2+ispalegreen,usedinthemanufactureofmargarine

• Fe2+ isgreen,usedintheHaberprocess

• Fe3+isreddish-brown

• Mn2+ ispalepink

Typicalproperties

• Manyhavedifferent ionpossibilitieswithdifferent

charges• Usedascatalysts

• Formcolouredcompounds

better hope – brighter future

AQABONDING,

STRUCTUREANDTHEPROPERTIESOFMATTER1

Thethree

statesofm

atter

Ionic Particlesareoppositely

chargedions

Occursincompoundsformedfrommetalscombinedwith

nonmetals.

Covalent

Particlesareatomsthatsharepairs ofelectrons

Occursinmostnonmetallicelementsandincompoundsof

nonmetals.

Metallic Particles areatomswhich

sharedelocalisedelectrons

Occursinmetallicelementsandalloys.

Ionicbonding

Ioniccompounds

Metallic

bond

ing

Prop

ertie

sofion

ic

compo

unds

Chemical

bonds

Electronsaretransferredsothatallatomshaveanoblegas configuration(fullouter

shells).

Metalatomsloseelectronsandbecomepositivelychargedions Group1metalsform+1ions

Group2metalsform+2ions

Nonmetalsatomsgainelectronstobecomenegativelychargedions Group6nonmetalsform -2ions

Group7nonmetalsform-1ions

Dotandcross

diagram

Giantstructure

Na+ Cl-

Structure

• Heldtogether bystrongelectrostaticforcesof

attractionbetweenoppositelychargedions

• Forcesactinalldirectionsinthelattice

High meltingandboilingpoints

Largeamountsofenergyneeded tobreakthebonds.

Donotconduct electricitywhensolid

Ionsareheldinafixedpositioninthe latticeandcannotmove.

Doconductelectricitywhenmoltenordissolved

Latticebreaksapart andtheionsarefreetomove.

Giantstructureofatoms

arrangedinaregularpattern

Electronsintheoutershellofmetalatomsare

delocalisedandfreetomovethroughthewholestructure.Thissharingofelectronsleadstostrong

metallicbonds.

Prop

ertie

sof

metalsa

ndallo

ys

Metalsasconductors

Goodconductorsofelectricity

Delocalisedelectronscarryelectricalchargethroughthemetal.

Goodconductorsofthermalenergy

Energyistransferredbythedelocalised

electrons.

High meltingandboiling

points

This isduetothestrongmetallic

bonds.

Puremetalscan bebentandshaped

Atomsarearrangedinlayersthatcanslideovereach

other.

Alloys

Mixtureoftwoormoreelementsat

leastoneofwhichisametal

Harderthanpuremetalsbecauseatoms ofdifferentsizesdisruptthelayerssotheycannotslide

overeachother.

s solid

l liquid

g gas

Solid,liquid,gas

Meltingandfreezing happenatmeltingpoint,boilingand

condensinghappenatboilingpoint.

Theamountofenergyneededforastatechangedependsonthestrengthofforces between

particlesinthesubstance.

(HTonly)Limitationsofsimple model:• Therearenoforcesinthe

model• Allparticlesareshownas

spheres• Spheresaresolid

PuremetalAlloy

Na NaCl Clx

xx

xxxx

xx

xx

xxx[ [ ]] -+

(2,8,1) (2,8,7) (2,8) (2,8,8)

better hope – brighter future

AQABONDING,STRUCTUREANDTHEPROPERTIES

OFMATTER2

Diamond

Covalent

bond

ing

Usuallygasesorliquids Covalentbonds

inthemoleculearestrongbutforcesbetween

molecules(intermolecular)

areweak

Lowmeltingandboilingpoints.

Due tohavingweakintermolecularforcesthateasily

broken.

Donotconductelectricity.

Duetothemmoleculesnot

havinganoverallelectricalcharge.

Largermoleculeshavehighermeltingandboilingpoints.

Intermolecularforcesincreasewith

thesizeofthemolecules.

Polymers

Giantcovalen

tstructures

Diamond,graphite,silicon

dioxide

Veryhighmeltingpoints

Lotsofenergyneededtobreakstrong,covalent bonds.

Propertiesofsmallm

oleculesAtom

ssha

repairsofe

lectrons

Canbesmallmolecules

e.g.ammonia

Canbegiantcovalentstructures

e.g.polymers

Grapheneand

fullerenes

Graphite

Useofnanoparticles

Sizeofparticlesandtheirproperties(Chemistryonly)

Eachcarbonatomisbondedtofourothers

Veryhard. Rigidstructure.

Veryhighmeltingpoint. Strongcovalentbonds.

Doesnotconductelectricity. Nodelocalisedelectrons.

Eachcarbon atomisbondedtothreeothersforming

layersofhexagonalringswithnocovalentbonds

betweenthelayers

Slippery. Layerscanslideovereachother.

Veryhighmeltingpoint. Strongcovalentbonds.

Doesconductelectricity.

Delocalisedelectronsbetweenlayers.

Verylargemolecules

Solidsatroom

temperature

Atomsarelinkedbystrongcovalent

bonds.

Grap

hene

Single layerofgraphiteoneatomthick

Excellentconductor.

Containsdelocalisedelectrons.

Verystrong.

Containsstrongcovalentbonds.

Fullerene

s Buckminsterfullerene,C60

Firstfullerenetobediscovered.

Hexagonalringsofcarbonatomswithhollow

shapes.Canalsohaveringsoffive(pentagonal)or

seven(heptagonal)carbonatoms.

Carbon

nan

otub

es

Verythinandlong

cylindricalfullerenes

Veryconductive. Usedinelectronicsindustry.

Hightensilestrength. Reinforcingcompositematerials.

Largesurfaceareatovolumeratio.

Catalystsandlubricants.

Nan

opartic

les

Between1and100nanometres(nm)in

size

1nanometre(1nm)=1x10-9 metres

(0.000000001morabillionthofametre).

Healthcare,cosmetics,sun cream,catalysts,

deodorants,electronics.

Nanoparticlesmaybetoxictopeople.Theymaybeabletoenterthebrainfromthe

bloodstreamandcauseharm.

2Dwithbonds:+Showwhichatomsarebondedtogether- ItshowstheH-C-Hbondincorrectlyat90°

3Dballandstickmodel:+AttemptstoshowtheH-C-Hbondangleis109.5°

Dotandcross:+Showwhichatomtheelectronsinthebondscomefrom

- Allelectronsareidentical

better hope – brighter future

AQAGCSEQUANTITATIVECHEMISTRY1

Conservationofmass

andbalancedsymbol

equations

Conservationofmass

Noatomsarelostormadeduringa

chemicalreaction

Massoftheproducts equalsthemassofthereactants.

Relativeformula

mass(M

r )

Masschangeswhenareactantorproductisagas

Moles(HTonly)

Amountsof

substancesinequations(HTonly) U

singm

olesto

ba

lanceeq

uatio

ns

(HTon

ly)

Limitingreactants(HTonly)

Balanced

symbo

leq

uatio

ns

Representchemical

reactions andhavethesamenumberof

atomsofeachelementonboth

sidesoftheequation

H2 +Cl2 à 2HCl

Subscriptnumbers showthenumberofatomsoftheelementtoitsleft.

Normalscriptnumbersshowthenumberofmolecules.

SubscriptNormalscript

Mr

Thesum oftherelativeatomicmassesoftheatomsinthenumbersshownintheformula

ThesumoftheMrofthereactantsinthequantitiesshownequalsthesumoftheMr oftheproductsinthequantitiesshown.

2Mg+O2 à 2MgO

48g+32g=80g

80g=80g

Massappears toincreaseduringa

reaction

Oneofthereactantsisagas Magnesium+ oxygenàmagnesiumoxide

Massappears todecreaseduringa

reaction

Oneoftheproductsisagasandhas

escapedCalciumcarbonateà carbondioxide+ calciumoxide

Chemicalamountsaremeasuredinmoles

(mol)

Massofonemoleofasubstanceingrams=relativeformulamass

OnemoleofH2O=18g(1+1 +16)

OnemoleofMg=24g

Avogad

roconstant Onemoleofanysubstancewill

containthesamenumberofparticles,atoms,moleculesorions.

6.02x1023 permole

OnemoleofH2Owillcontain6.02x1023 moleculesOnemoleofNaCl willcontain6.02x1023 Na+ ions

Numberofmoles=mass(g) ormass(g)Ar Mr

Howmanymolesofsulfuric acidmoleculesaretherein4.7gofsulfuric acid(H2SO4)?

Giveyouranswerto1significantfigure.

4.7 =0.05mol98(MrofH2SO4)

Thereactantthat iscompletelyusedup

Limitstheamountofproductthatismade

Lessmolesofproductaremade.

Concentrationofsolutions

The balancingnumbersinasymbolequationcanbe

calculatedfromthemassesofreactantsandproducts

Convertthemassesingramstoamountsinmolesandconvertthenumberofmolestosimple

wholenumberratios.

Chem

icalequ

ationssh

owth

enu

mbe

rofm

oles

reactin

gan

dthenu

mbe

rofm

olesm

ade

Mg+2HClàMgCl2 +H2

Onemoleofmagnesiumreactswithtwomolesofhydrochloric

acidtomakeonemoleofmagnesiumchlorideandone

moleofhydrogen

Ifyouhavea60gof Mg,whatmassofHCl doyouneedtoconvertittoMgCl2?

Ar :Mg=24somassof1moleofMg=24gMr :HCl (1+35.5)somassof1moleofHCl =36.5g

So60gofMgis60/24=2.5moles

BalancedsymbolequationtellsusthatforeveryonemoleofMg,youneedtwomolesofHCl toreactwithit.

Soyouneed2.5x2=5molesofHCl

Youwillneed5x36.5gofHCl=182.5g

Measuredinmasspergivenvolumeof

solution(g/dm3)

Conc.=mass(g) .volume(dm3)

HTonlyGreatermass=higher

concentration.Greatervolume=lower

concentration.

Chemicalm

easurements

Wheneverameasurementistaken,thereisalwayssomeuncertainty

abouttheresultobtained

Candeterminewhetherthemean

valuefallswithintherangeofuncertainty

oftheresult

1. Calculate themean2. Calculatetherange

oftheresults3. Estimateof

uncertaintyinmeanwouldbehalftherange

Example:1. Meanvalueis46.5s

2. Range ofresultsis44sto49s=5s3. Timetakenwas46.5s±2.5s

better hope – brighter future

AQAQUANTITATIVECHEMISTRY2

Yield istheamountofproductobtained

Itisnotalwayspossibletoobtainthecalculatedamountofaproduct

Thereactionmaynotgotocompletionbecauseitisreversible.

Someoftheproductmaybelostwhenitisseparatedfromthereactionmixture.

Someofthereactantsmayreactinwaysdifferenttothe expectedreaction.

Percentageyield

Atomeconom

y

Usingconcentrationsofsolutionsinmol/dm3

(HTonly,chemistryonly)

Useofamountofsubstanceinrelationtovolumesofgases(HTonly,chemistryonly)

Percentageyieldiscomparingthe

amountofproductobtainedasa

percentageofthemaximum

theoreticalamount

%Yield=Massofproductmadex100Max.theoreticalmass

Apieceofsodiummetalisheatedinchlorinegas.Amaximumtheoreticalmassof10gforsodiumchloridewascalculated,buttheactualyieldwas

only8g.Calculatethepercentageyield.

Percentageyield=8/10x100 =80%

HT only:200gofcalciumcarbonateisheated.Itdecomposestomakecalciumoxideandcarbondioxide.Calculatethetheoreticalmassofcalciumoxidemade.

CaCO3 à CaO +CO2Mr ofCaCO3 =40+12+(16x3)=100Mr ofCaO =40+16=56100gofCaCO3 wouldmake56gofCaOSo200gwouldmake112g

Ameasureoftheamountofstartingmaterialsthatendupasusefulproducts

Atomeconomy=Relativeformulamassofdesiredproductfromequation x100Sumofrelativeformulamassofallreactantsfromequation

High atomeconomyisimportantorsustainable

developmentandeconomicreasons

Calculatetheatomeconomyformakinghydrogenbyreactingzincwithhydrochloricacid:

Zn+2HCl→ZnCl2 +H2

Mr ofH2 =1+1=2Mr ofZn +2HCl =65+1+1+35.5+35.5= 138

Atomeconomy= 2∕138 × 100= 2∕138 × 100=1.45%

Thismethodisunlikelytobechosenasithasalowatomeconomy.

Concentrationofasolutionistheamountofsoluteper

volumeofsolution

Concentration =amount(mol)(mol/dm3)volume(dm3)

Whatistheconcentrationofasolutionthathas35.0gofsolutein0.5dm3ofsolution?

35/0.5=70g/dm3

Titration

Ifthevolumesoftwosolutionsthatreactcompletelyareknownandtheconcentrationsofonesolutionisknown,the

concentrationoftheothersolutioncanbecalculated.

2NaOH(aq)+H2SO4(aq)→Na2S04(aq) +2H2O(l)

Ittakes12.20cm3 ofsulfuric acidtoneutralise24.00cm3ofsodiumhydroxidesolution,whichhasaconcentrationof

0.50mol/dm3.

Calculatetheconcentrationofthesulfuric acidinmol/dm3:

0.5mol/dm3 x(24/1000)dm3 =0.012mol ofNaOHTheequationshowsthat2mol ofNaOH reactswith1mol ofH2SO4,sothenumberofmolesin12.20cm3 ofsulfuric acidis

(0.012/2)=0.006mol ofsulfuric acid

Calculatetheconcentrationofsulfuric acidinmol/dm3

0.006mol x(1000/12.2)dm3=0.49mol/dm3

Calculatetheconcentrationofsulfuric aciding/dm3:

H2SO4=(2x1)+32+(4x16)=98g0.49x98g=48.2g/dm3

Equalamountsofmolesorgasesoccupy

thesamevolumeunderthesameconditionsof

temperatureandpressure

Thevolumeofonemoleofanygasatroomtemperatureandpressure(20°Cand1

atmosphericpressure)is24dm3

No.ofmolesofgas=vol ofgas(dm3)24dm3

Whatisthevolumeof11.6gofbutane(C4H10)gasatRTP?

Mr:(4x12)+(10x1)= 58

11.6/58= 0.20mol

Volume=0.20x24= 4.8dm3

6gofahydrocarbongashadavolumeof4.8dm3.Calculateitsmolecularmass.

1mole=24dm3,so4.8/24=0.2mol

Mr =6/0.2= 30

If6g=0.2mol,1mol equals30g

better hope – brighter future

AQAChemicalChanges1

Metaloxides

Reactivityofmetals

Metalsformpositiveionswhenthey

react

Thereactivityofametal isrelatedtoitstendencytoformpositiveions

Thereactivityseriesarrangesmetalsinorderoftheirreactivity(theirtendencytoformpositiveions).

Carbon andhydrogen

Carbon andhydrogenarenon-metalsbutare

includedinthereactivityseries

Thesetwonon-metalsareincludedinthereactivityseriesasthey canbeusedtoextractsomemetalsfromtheirores,dependingontheirreactivity.

Displacement

Amorereactive metalcandisplacealess

reactivemetalfromacompound.

Silvernitrate+Sodiumchlorideà

Sodium nitrate+Silverchloride

Metalsandoxygen

Metalsreactwithoxygentoformmetal

oxides

magnesium +oxygenàmagnesiumoxide2Mg+O2 à 2MgO

Reduction

Thisis whenoxygenisremovedfroma

compoundduringareaction

e.g.metaloxidesreactingwithhydrogen,extractinglowreactivitymetals

OxidationThisiswhenoxygenisgainedby acompound

duringareaction

e.g.metalsreactingwithoxygen,rustingofiron

Thereactivityseries

Extractionusingcarbon

Metalslessreactivethancarboncanbeextractedfromtheiroxidesby

reduction.

Forexample:zinc oxide+carbonà zinc+carbondioxide

Reactions withwater Reactionswithacid

Group1metalsReactions getmore

vigorousasyougodownthegroup

Reactionsgetmorevigorous asyougodown

thegroup

Group2metals Do notreactwithwaterObservable reactionsincludefizzingand

temperatureincreases

Zinc, ironandcopper Donotreactwithwater

Zinc andironreactslowlywithacid.Copperdoesnot

reactwithacid.

Extractionofmetalsandreduction

Reactionswithacids

metal+acidà metalsalt+hydrogen

magnesium +hydrochloricacidàmagnesiumchloride+hydrogen

zinc+sulfuricacidà zincsulfate+hydrogen

Ionichalfequations(HTonly)

Fordisplacementreactions

Ionic halfequationsshowwhathappenstoeachofthe

reactantsduringreactions

For example:The ionicequationforthereactionbetweenironandcopper(II)ionsis:

Fe+Cu2+à Fe2+ +Cu

The half-equationforiron(II)is:Feà Fe2+ +2e-

Thehalf-equationforcopper(II)ionsis:Cu2+ +2e-à Cu

Unreactivemetals,suchasgold,arefoundintheEarthasthemetalitself.Theycanbeminedfromtheground.

Oxidationandreductionintermsofelectrons(HTONLY)

OxidationIsLoss(ofelectrons)ReductionIsGain(ofelectrons)

Reactionsofacidsandmetals

Acidsreactwithsomemetalstoproducesaltsandhydrogen.

HTONLY:Reactionsbetweenmetalsandacidsareredoxreactionsasthemetaldonateselectronstothehydrogenions.Thisdisplaceshydrogenasagaswhilethemetalionsareleftinthesolution.

Neutralisationofacidsandsaltproduction

Neutralisation

Acidscanbe

neutralisedbyalkalisandbases

Analkali isasolublebasee.g.metalhydroxide.Abase isasubstancethatneutralises anacide.g.asolublemetalhydroxideorametaloxide.

Acidname Salt name

Hydrochloricacid Chloride

Sulfuric acid Sulfate

Nitricacid Nitrate

sodiumhydroxide+hydrochloricacidà sodiumchloride+water

calciumcarbonate+sulfuricacidà calciumsulfate,+carbondioxide+water

Reactionsofacids

better hope – brighter future

AQAChemicalChanges2

Solublesalts

Reactionsofacids

Solublesalts

Solublesaltscan bemadefromreactingacidswithsolidinsolublesubstances(e.g.metals,metaloxides,hydroxides

andcarbonates).

Productionofsolublesalts

Addthesolidtotheaciduntilnomoredissolves.Filteroffexcesssolidandthen

crystallise toproducesolidsalts.

ThepHscaleandneutralisation

Acids Acidsproducehydrogenions (H+)inaqueoussolutions.

Alkalis Aqueous solutionsofalkaliscontainhydroxideions(OH-).

YoucanuseuniversalindicatororapHprobetomeasuretheacidityoralkalinityofasolutionagainstthepHscale.

Inneutralisationreactions,hydrogenionsreactwithhydroxideionstoproducewater:

H+ +OH- à H2O

Titrations(Chemistry

only)

Titrationsareusedtoworkouttheprecisevolumesofacidandalkalisolutionsthatreactwitheachother.

Calculatingthechemicalquantitiesintitrationsinvolvingconcentrationsin

mol/dm3 and ing/dm3

(HTONLY):2NaOH(aq)+H2SO4(aq)→Na2S04(aq) +

2H2O(l)

Ittakes12.20cm3 ofsulfuric acidtoneutralise24.00cm3ofsodiumhydroxidesolution,which

hasaconcentrationof0.50mol/dm3.

Calculatetheconcentrationofthesulfuric aciding/dm3

0.5mol/dm3 x(24/1000)dm3 =0.012mol ofNaOH

Theequationshowsthat2mol ofNaOH reactswith1mol ofH2SO4,sothenumberofmolesin12.20cm3 ofsulfuric acidis(0.012/2)=

0.006mol ofsulfuric acid

Calculatetheconcentrationofsulfuric acidinmol/dm3

0.006mol x(1000/12.2)dm3=0.49mol/dm3

Calculatetheconcentrationofsulfuric aciding/dm3

H2SO4=(2x1)+32+(4x16)=98g0.49x98g=48.2g/dm3

1.Usethepipettetoadd25cm3 ofalkalitoaconicalflaskandaddafewdropsof indicator.

2.Fillthe burette withacidandnotethestartingvolume.Slowlyaddtheacidfromtheburettetothealkaliinthe

conicalflask,swirlingtomix.

3.Stopaddingtheacidwhentheend-pointisreached(theappropriatecolourchangeintheindicatorhappens).Notethefinalvolumereading.Repeatsteps1to3untilyouget

consistentreadings.

Strongandweakacids

(HTONLY)

Strongacids Completelyionisedinaqueoussolutionse.g.hydrochloric,nitric andsulfuricacids.

Weakacids Onlypartiallyionised inaqueoussolutionse.g.ethanoic acid,citricacid.

Hydrogen ionconcentration

AsthepHdecreasesbyone unit(becomingastrongeracid),thehydrogenion

concentrationincreasesbyafactorof10.

Electrolysis

Processofelectrolysis

Splittingupusing

electricity

Whenanioniccompoundismeltedordissolvedinwater,theionsarefreetomove.Thesearethenabletoconductelectricityandarecalledelectrolytes.

Passinganelectriccurrentthoughelectrolytescausestheionstomovetotheelectrodes.

Electrode AnodeCathode

The positiveelectrodeiscalledtheanode.Thenegativeelectrodeiscalledthecathode.

Where dotheionsgo?

CationsAnions

Cationsarepositiveionsandtheymovetothenegativecathode.

Anionsarenegativeionsandtheymove tothepositiveanode.

Highertier:Youcandisplaywhatishappeningateachelectrodeusinghalf-equations:Atthecathode:Pb2++2e- à PbAttheanode:2Br- à Br2 +2e-

Extractin

gmetalsu

sing

electrolysis

Metals canbeextractedfrommoltencompoundsusingelectrolysis.

Thisprocessisusedwhenthemetalistooreactivetobeextractedbyreductionwith

carbon.

Theprocessisexpensiveduetolargeamountsofenergyneededtoproducethe

electricalcurrent.Example:aluminiumisextractedinthis

way.Electrolysisofaqueoussolutions

Atthenegativeelectrode

Metalwillbeproducedontheelectrodeifitislessreactivethanhydrogen.

Hydrogenwillbeproducedifthemetalismorereactivethanhydrogen.

Atthepositiveelectrode

Oxygenisformedatpositiveelectrode.Ifyouhaveahalideion(Cl-,I-,Br-)thenyouwillgetchlorine,bromineoriodine

formedatthatelectrode.

Theionsdischargedwhenanaqueoussolutioniselectrolysedusinginertelectrodesdependontherelativereactivityoftheelementsinvolved.

+_

+-

-

--

-+

++

+

Moltenlead(II)bromide

BromideionsBr-LeadionsPb +

better hope – brighter future

AQAGCSEEnergychanges

Endothermic

Energyistakeninfromthesurroundingssothetemperatureofthe

surroundingsdecreases

• Thermaldecomposition• Sportsinjurypacks

Exothermic

Energyistransferredtothesurroundingssothetemperatureofthe

surroundingsincreases

• Combustion• Handwarmers• Neutralisation

Typesofreaction

Reactionprofiles

Theenergychangeofreactions(HTonly)

Cellsandbatteries(Chemistryonly)

Fuelcells(Chemistryonly)

Activ

ationen

ergy

Chemicalreactionsonlyhappen whenparticlescollidewithsufficient

energy

Theminimumamountof energythatcollidingparticlesmusthaveinordertoreactiscalledtheactivationenergy.

Endo

thermic

Productsareatahigherenergylevel thanthereactants.Asthereactantsformproducts,energy

istransferredfromthesurroundingstothereaction

mixture.Thetemperatureofthesurroundingsdecreasesbecauseenergyistakeninduringthe

reaction.

Exothe

rmic

Productsareatalowerenergylevelthanthereactants.Whenthereactantsformproducts,energyistransferredtothe

surroundings.Thetemperatureofthesurroundingsincreasesbecauseenergyisreleased

duringthereaction.

Reactionprofiles

Showtheoverallenergychangeofareaction

Breakingbondsinreactants Endothermicprocess

Makingbondsinproducts Exothermic process

Overallen

ergycha

nge

ofare

actio

n

ExothermicEnergyreleasedmakingnewbondsisgreaterthantheenergytaken inbreaking

existingbonds.

EndothermicEnergyneededtobreakexisting

bondsisgreaterthantheenergyreleasedmakingnew

bonds.

Hydrog

enfu

elcells Wordequation:

hydrogen+oxygenà water

Symbolequation:

2H2+O2 à 2H2O

Advantages:• Nopollutantsproduced• Canbearangeofsizes

Disadvantages:• Hydrogenishighlyflammable• Hydrogenisdifficulttostore

Ionicha

lfeq

uatio

ns Negativeelectrode:2H2 (g)+4OH- (aq)à 4H2O(l)+4e-

Positiveelectrode:O2 (g)+2H2O(l)+4e- à 4OH- (aq)

Non

-recha

rgeable

cells

Stopwhen oneofthereactantshasbeen

usedupAlkalinebatteries

Rechargeab

lecells Canberecharged

becausethechemicalreactionsarereversedwhenanexternalelectricalcurrentis

supplied

Rechargeablebatteries

Simplecell Makeasimplecell byconnecting twodifferentmetalsincontactwithan

electrolyte

Increasethevoltageby

increasingthereactivitydifference

betweenthetwometals.

Batteries Consistoftwoor more

cellsconnectedtogetherinseriestoprovideagreatervoltage.

Bond

ene

rgycalculation

CalculatetheoverallenergychangefortheforwardreactionN2 +3H2⇌2NH3

Bondenergies(inkJ/mol):H-H436,H-N391,N≡N945

Bondbreaking:945+(3x436)=945+1308=2253kJ/mol

Bondmaking: 6x391=2346kJ/mol

Overallenergychange=2253- 2346=-93kJ/mol

Thereforereactionisexothermicoverall.