RDC 9729_02 H2 Chemistry Practice 1 QP

1 CHEMISTRY 9729/02Paper2StructuredQuestions 2hoursCandidatesansweronQuestionPaper READTHESEINSTRUCTIONSFIRSTAnswer ALLquestions.Themaximummarksawardedperquestionisindicatedinthesquarebracketsattheendofeachquestion. Donot turnover thebooklet until youaretoldtodoso.Thisdocumentconsistsof 26printedpages,includingthisCoverPage,and1blankpage.

2 QUESTION1Squaricacidisadiproticorganicacid.Figure1.1showstheskeletalformulaofsquaricacid. Figure1.1 (a)(i)Suggestwhattheterm‘diproticorganicacid’means. ……………………………………………………………………………………………………………… …………………………………………………………………………………………………………….[1] (ii)Statethebondanglebetweentwoadjacentcarbonatoms.Explainyouranswer. ……………………………………………………………………………………………………………….. .………………………………………………………………………………………………………………. ..……………………………………………………………………………………………………………… …………………………………………………………………………………………………………….[2] (b)(i)Squaricacidisnotaperfectsquarebecauseoftheunequalbondlengthsbetweenanytwoadjacentcarbonatoms.Explainwhythisoccurs. .………………………………………………………………………………………………………………. ..……………………………………………………………………………………………………………… …………………………………………………………………………………………………………….[1]

3 (ii)Figure1.2showstheresonancestabilisationofthedivalentsquarateanion.Draw,onFig1.2,curlyarrowsandlonepairstoshowhowthisresonancestabilisationisachieved,fromlefttoright. Figure1.2 [1] (iii)Hence, consideringboth(i)and(ii), explainwhythedivalentsquarateanionisaperfectsquare. .………………………………………………………………………………………………………………. ..……………………………………………………………………………………………………………… …………………………………………………………………………………………………………….[1] (c)ComparethepHof1molofsquaricacid1molofethanoicacid,ofequalconcentration.Explaintworeasons. ……………………………………………………………………………………………………………….. .………………………………………………………………………………………………………………. ..……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………….. .………………………………………………………………………………………………………………. ..……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………….. .………………………………………………………………………………………………………………. ..……………………………………………………………………………………………………………… …………………………………………………………………………………………………………….[2]

4 Thedivalent squarateanionisanexampleof theoxocarbonanion,whichisanegativeionconsistingsolelyofcarbonandoxygenatoms,andthereforehavingthegeneralformulaCx Oy n− forsomeintegersx,y,andn.(d)(i)Suggeststructuresforthefollowingoxocarbonanions:● dicarbonate(C2 O5 2− )● ethylenetetracarboxylate(C6 O8 4− ),and● benzenehexolate(C6 O6 6− ). [2] Everyoxocarbonanioncanbematchedinprincipletotheelectricallyneutral variant Cx Oy ,knownastheneutralisedspecies. (ii) By using one of the oxocarbon anions in (i), explainwhether ‘neutralising’ anoxocarbonanionisanoxidationorreductionreaction.Hence,explainwhyasarule,theneutralisedspeciesismoreunstablethantheircorrespondingoxocarbonanion. ..……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………….. .………………………………………………………………………………………………………………. ..……………………………………………………………………………………………………………… …………………………………………………………………………………………………………….[2]

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6 (iii)Eachoxocarbonanioncanalsoformacorre