H2 Chem Practical (1)

EXPERIMENTALPROCEDURES Titration 1.SF,DP ○ Burette–2d.p. ■ Allnumbersshouldeitherendwith.00or.05–notewhenuarefakingyourdata ○ Pipette–1d.p. ○ Temperature–1dp(halfof0.2degcel) ○ Mr–1dp,nounits 2.Notes ○ Remembertowriteunitsforcalculations–writeatthestartofthepaper+signs(theyseemtostressnegative/positivesignalotforqns,includingchangeintemp/gradientqns,somakesuretoinclsignsaswell) ○ Don’tstressifstuckatmolecalculations,readquestion,readprovidedinfo,understandaimofexperiment ○ Ifuusesolidtomakeastandardsolution,rememberthatinurcalculations,useurmeasuredmassofsolidandnotthemassuweresupposedtoadd. ○ Calculating%uncertainty: ■ Absoluteuncertainty=(½smallestdivision)x(numberofreadings) ■ Burettevolumerequires2readings,so±0.05x2.Masschange/lossalsorequires2readings.Pipetteonlyrequires1readingso0.1x1. ■ Inyourworkingandfinalanswer,remembertoadd±. ■ Egqn:whichpieceofapparatuscausesthegreatestpercentageerrorinyourexperiment?→askingforutocalculateandcompare%uncertainties. ● Enthalpy=mc(changeinT)/amountofLR:whencalculating%ucofchangeinT,needtox2tothe½ofsmallestdivision. ○ %error(difference):

2 ■ noneed± ■ 3sf ○ Ifqngivesumassofacompoundthathaswaterofcrystallisation,theMrthatudividebymustincludemassofwaterofcrystallisation! ○ Ifaskedtocalculatenumberofmolesofelectrons,leaveaswholenumber,cuzoxidationstatesonlyexistaswholenumbers. ○ Memoriseindicatorsandtheircolours(foruniversalindicator,checkthecolourofthepaperagainstthechartofpHvaluesgivenandstatethepHvalue)–methylorangeforacidic||thymolblueandphenolphthaleinforalkaline ○ Ifurnotsurewhatgastotestfor,lookattheeqnatthestartofthepractical→givesyoutheproductstotestfor ○ Whenqnsays‘calculate___change’,makesureyourfinalanswerhasa+/-signtoindicatewhetherthevalueincreasedordecreased. ○ Ifquestionsasksaboutwhythissolutionisacidic,explainintermsofcharge/sizeratio,highcharge/size,letsitpolariseandweakensO-HbondinH2O,causingittoundergohydrolysistogive[complexion],makingitanacidicsolution ○ Forplanningqns,rmbtodrawyourtable ○ Ifaskedtheroleofxyzinaparticularreaction,it’smostlyeitheracatalystoranacid/baseoraR.A/O.A.. ○ Tworeadingsfromaninstrumentmeanstheoveralluncertaintyis2xtheuncertaintyoftheinstrument ○ Ifyoupouroutasolidfromabottleandtheqnasksyoutoweighthebottleafterpouring,inyourtable,youmustplotas“massofemptybottle+RESIDUE”–thisisbecausethereisboundtoberesidueafterpouringasolidout. ○ Youquenchamixturebyeitherdilutingthesolutioninalargeamountofsolvent(likewater)orremovingthecatalystsothatreactionstopshappening. ○ Tabulationofdataandgraphingisahugechunkofmarksforprac,somakesureyoudon’tloseanysillymarksthere.

3 ○ Forinitialratesmethod,youhavetouserateagainstconcgraphtodeterminetheorder(ifthelineisastraightlinepassingthroughtheorigin,thisisfirstorder).Forcontinuousmethod,youwoulduseaconcagainsttimegraph(ifcurvehasaconstanthalflifeoft1/2,thenitisfirstorder). ○ BeSUPERCLEARaboutyourapparatusinyourplanningqn-eg.250cm^3conicalflask,100cm^3measuringcylinder,etc.Don’tlosesillymarksoverthis:( Theyaskedthelasteqnbefore,somaybei