ZNOTES.ORGUPDATED TO 2019-21 SYLLABUSCAIE A2 LEVELCHEMISTRY(9701)SUMMARIZED NOTES ON THE PRACTICAL SYLLABUSCAIE A2 LEVEL CHEMISTRY(9701)Mean1.Planning1.1.Defining the Problem (4 Marks)Median:middle result when results in ascending orderMode:most common value.Percentage Gain/Loss:the independent variable in the experimentthe dependent variable in the experimentActual Loss GainPercentage Gain/Loss×100the quantities to be controlled-kept constantOriginal AmountFormulate the aim in terms of a prediction or ahypothesis,and express this in words or in the form of a2.2.Evaluation (4 Marks)predicted graphThe hypothesis is usually a short statement showing theIdentify anomalous values in provided data and suggestrelationship (e.g.proportional)between two variables.appropriate means of dealing with such anomaliesExplain your hypothesis using scientific knowledgeSuggest possible explanations for anomalous readingsThe rate of reaction collision theoryIdentify the extent to which provided readings have been·Enthalpy of solution=ionic radii△Hhyd and△Hiatadequately replicated,and describe the adequacy of the·Group2=radirange of data providedUse provided information to assess the extent to which1.2.Methods(8 Marks)selected variables have been effectively controlledDescribe the methods to be used to vary the independent2.3.Conclusion (2 Marks)variable,and the means that you propose to ensure thatyou have measured its values accuratelyDraw conclusions from an investigation,providing aDescribe how you will measure the dependent variabledetailed description of the key features of the data andDescribe how you will control each of the other variablesanalyses,and considering whether experimental dataExplain how you will use any control experiments to verifysupports the condusion reachedthat it is the independent variable that is affecting theMake detailed scientific explanations of the data,dependent variable and now some other factorDescribe the arrangement of apparatus and the steps inMake further predictions,ask informed and relevantthe procedure to be followedquestions,and suggest improvementsSuggest appropriate volumes and conc.of reagentsAssess the risks of your proposed methods2.4.TablesDescribe precautions that should be taken to keep risksto a minimumLabel each column with:Draw up tables for data that you might wish to recorda description (e.g.concentration of acid in water)Describe how the data might be used in order to reach a·a unit(eg./mol dm-3)conclusionan expression to calculate the data (e.g.Bx 0.1/20)Make sure values calculated is to s.f./d.p.required in the2.Analysis,Conclusions andquestionEvaluation2.5.GraphsIndependent variable plotted on the x-axis and the2.1.Dealing with Data (6 Marks)dependent on the y-axisAppropriate scale;1 large box=1,2,4 or 5.Identify the calculations and means of presentation ofThe graph must cover at least half the grid in bothdata that are necessary to be able to draw concusionsdirectionsfrom provided dataIf experiment/relationship shows origin(0,0)is a validUse calculations to enable simplification or explanation ofpoint,scaling must include origin line should include itdataas it is a definite point not subject to experimental errorsUse tables graphs to draw attention to the key points inWhen referring to an anomalous result,clearly define thequantitative data,induding the variability of datapoint before stating the reasonWhen calculating gradient,show construction lines andCalculations may include:hypotenuse must be greater than half the lineWWW.ZNOTES.ORGCAIE A2 LEVEL CHEMISTRY (9701)3.Details and MethodsWhen collecting gas over water:potential suck back soremove delivery tube from water when heating stopsSolution boils over/sprays:use gloves,eye protection3.1.General InformationCorrosive nature of reagents:use glovesUse a burette/pipette to measure volumes as they have3.4.Anomalous Points on the Graphlow errorsUsing a 3 d.p.balance rather than a 2 d.p.balanceA particular measurement is done before or after thereduces errormoment it should be donePercentage errors very high with very smallvolumes/massesoxidation/reductionHeating crystals strongly;use a crucible placed on a pipe·decompositionclay triangle·reactionAllow crucible to cool on heat mat before placing onLoss of water/chemicalbalance to measure the massAcompound has decomposedUse sandpaper to clean the surface of metal e.g.A solution has not been saturatedmagnesium ribbon (remove oxide layer)Not all the water in the solution has been evaporatedMaximum temperature difficult to determine so instead,Crystals not adequately dried(propanone or water)take readings at regular intervalsSolid blown out of the tube by not heating gentlyThe temperature of the solution is not uniform so stir thesolution throughout the experiment3.5.Removing MoistureNo need to measure mass/volume of reagents in excessFlush out oxygen from a system using an inert gas(used·From surface:in reduction experiment of metal oxides)Wash surface with a stream of propanoneTo collect water vapor as a liquid,collect in a beakerPropanone dissolves the water-repeat several timesplaced in an ice bath (Liebig condenser)Gently heat the surface to evaporate propanone fromUse a divided flask to keep reagents separate-shake tosurfacebegin reaction start time immediately;no gas escapesFrom vapours:pass vapour through beaker containing aIf syringe gives incorrect value,could be because it gotdesiccantstuck during the experimentAnhydrous sulphuric acidIf the percentage difference between the measuredAnhydrous calcium chloridetrue value·Silica gelMore than max apparatus eror,experimenter'sCan use soda lime:absorbs both water vapour andtechnique needs modificationcarbon dioxideLess than max apparatus error,due to an error inapparatus or simply random error3.6.Forming Specific Conc.SolutionsTo improve the accuracy of pH against volume curve,usedata logger interface and computer to plot the graphFrom a given parent solution3.2.Volumes of Apparatuse.g.250cm3 of 0.1 mol dm3 using a 2.0 mol dm3 solutionAlways mention the volume of apparatus being used◆Common volumes:2.0×x=250×0.1·Test tube-16cm3Gas syringe:100cm3 up to 500cm3t=12.5cm3·Glass beaker-250cm3Add 12.5cm3 of parent solution to a volumetric flaskPolystyrene cup=150cm3(250cm3)using a buretteCalculate quantities and show volume would not exceedthe apparatus usedFrom a solid3.3.Potential Risks and Solutionse.g.250cm3 of 0.5 mol dm3 solution of a crystal Mr =50gOxygen:is an oxidant so remove any oxidisable materialNitrogen dioxide:is poisonous so carry out anMols=0.5×0.25=0.125experiment in a fume cupboardWWW.ZNOTES.ORG