IB Chemistry Organic Chemistry Written

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Two reactions of an alkene, B, are shown below. (i) State the name of A and write an equation for its complete combustion. Explain why the incomplete combustion of A is dangerous.
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butane; C4H10(g) + O2(g) ? 4CO2(g) + 5H2O(l);
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(ii) Outline a test to distinguish between A and B, stating the result in each case.
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add Br2 (water); valid test needed to score further marks. A – no effect; B – would decolorise Br2 (do not accept discolour);
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(iii) Write an equation for the conversion of B to C. State the type of reaction taking place and draw the structure of C.
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CH3CH==CHCH3 + HBr ? CH3CHBrCH2CH3; 3 [1] for HBr in balanced equation, [1] for structure of product. addition;
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For the two compounds HCOOCH2CH3 and HCOOCHCH2: I II (i) State and explain which of the two compounds can react readily with bromine.
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(i) II reacts with Br2 II is an alkene/has unsaturated R group/CC present, I contains only saturated R groups;
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(ii) Compound II can form polymers. State the type of polymerization compound II undergoes, and draw the structure of the repeating unit of the polymer.
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(ii) addition polymerization;
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The compound C2H4 can be used as a starting material for the preparation of many substances. (a) Name the compound C2H4 and draw its structural formula.
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ethene
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(b) In the scheme below, state the type of reaction and identify the reagent needed for each reaction. A B C2H4 ? CH3CH2OH ? CH3COOH
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(b) A addition/hydration; H2O/water/steam; B oxidation; acidified K2Cr2O7 Accept acidified KMnO4.
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(c) C2H4 can be converted into one of the compounds below in a single step reaction. C2H3Cl C2H4Cl2 Draw the structural formula for each of these compounds and identify the compound which can be formed directly from C2H4.
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The compound formed directly may be circled or indicated by some 3 other means. Accept any other structure showing a Cl atom on each C atom.
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(d) One of the two compounds in (c) has an isomer. Draw the structural formula of the isomer and explain why it can not be formed directly from C2H4.
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addition across a double bond occurs at both C atoms/OWTTE; 2 If 1,1-dichloroethane is given in (c) accept 1,2-dichloroethane as the isomer as ECF but Award [1] max;
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(e) C2H4 can also react to form a polymer. Name this type of polymer and draw the structural formula of a section of this polymer consisting of three repeating units.
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(e) addition polymer; 2
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(f) Polymers can also be formed in a different type of reaction. Identify this type of reaction and name two different types of such polymers.
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(f) condensation polymer; polyesters; polyamides; 3
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The plastic PVC, poly(chloroethene), is made from the monomer chloroethene, C2H3Cl, by a polymerization reaction. (i) Draw the structural formula of chloroethene.
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CH2CHCl/CH2 = CHCl/;
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(ii) State the type of polymerization reaction that occurs to make poly(chloroethene) and identify the structural feature needed in the monomer.
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(ii) addition (polymerization); (carbon-carbon) double bond/unsaturation/OWTTE;
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(iii) Draw the structure of the repeating unit of poly(chloroethene).
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(iv) Explain why monomers are often gases or volatile liquids, whereas polymers are solids.
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(iv) monomers have smaller molecules/surface area than polymers; with weaker intermolecular/Van der Waals’ forces; 2 Accept opposite argument for polymers.
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The hydrolysis of 2-iodo-2-methylpropane by 0.10 mol dm-3 KOH(aq) to form 2-methylpropan-2-ol is an example of nucleophilic substitution. Give equations to illustrate the SN1 mechanism for this reaction.
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(CH3)3CI ? (CH3)3C+ + I?; (CH3)C+ + OH? ? (CH3)3COH; 2 Do not allow SN 2 reaction.
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The molecular formula c4h9br represents four structural isomers, all of which can undergo nucleophilic substitution reactions with aqueous sodium hydroxide. An equation to represent all these reactions is C4H9Br + NaOH ? C4H9OH + NaBr (a) Explain what is meant by the term nucleophilic substitution.
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(a) replacement of atom/group (in a molecule)/OWTTE; Do not accept substitution. by a species with a lone pair of electrons/species attracted to an electron-deficient carbon atom;
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(b) The main mechanism for a tertiary halogenoalkane is SN1. Give the equations for this substitution reaction of the tertiary isomer of C4H9Br. Show the structures of the organic reactant and product and use curly arrows to show the movement of electron pairs.
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correct structure of (CH3)3CBr; curly arrow showing C?Br bond fission; correct structure of (CH3)3C+; curly arrow showing attack by OH? on correct C atom; correct structure of (CH3)3COH; 4 Award [1] each for any four.
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(c) The main mechanism for a primary halogenoalkane is SN2. Give the mechanistic equation for this substitution reaction of the straight-chain primary isomer of C4H9Br, showing the structures of the organic reactant and product, and using curly arrows to show the movement of electron pairs.
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correct structure of CH3CH2CH2CH2Br; curly arrow showing C?Br bond fission; correct structure of transition state showing charge and all bonds; curly arrow showing attack by OH? on correct C atom; correct structure of CH3CH2CH2CH2OH;
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(d) Give a structural formula for the secondary isomer and for the other primary isomer. State the name of each isomer.
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(d) secondary CH3CHBrCH2CH3; 2-bromobutane; other primary (CH3)2CHCH2Br; 1-bromo-2-methylpropane;
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Write equations to show the mechanisms of the following reactions. In each case, show the structure of the intermediate and organic product, and use curly arrows to show the movement of electron pairs. (i) the reaction between KOH and CH3CH2CH2CH2Cl.
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(i) (SN2 mechanism) 3 Intermediate structure showing overall negative charge and partial bonds. Accept negative charge to be indicated as delocalised between the HO-CH2-Cl. ? HO ? CH2CH2CH2CH3 + Cl?;
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(ii) the reaction between KOH and (CH3)3CCl.
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(SN1 mechanism)
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Some alcohols are oxidized by heating with acidified potassium dichromate(VI). If oxidation does occur, identify the possible oxidation products formed by each of the alcohols below. Indicate if no oxidation occurs. Butan-1-ol
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butanal; butanoic acid;
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Butan-2-ol
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butanone;
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2-methylpropan-2-ol
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no oxidation
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Chlorine and ethane react together to form chloroethane. (a) State the condition needed for the reaction to occur.
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(a) UV light/sunlight (present); 1
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(b) Write equations to represent initiation, propagation and termination steps in the reaction.
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(b) Throughout accept radical with or without • initiation reaction(s): Cl2 ? 2Cl•; 1 propagation reactions: Cl• + CH3CH3 ? CH3CH2• + HCl; CH3CH2• + Cl2 ? CH3CH2Cl + Cl•;
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CH3COCH3 is the first member of the ketone homologous series. Draw the full structural formula of the next member of this homologous series and predict how its melting point compares with that of CH3COCH3.
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(i) Write an equation for the reaction between but-2-ene and bromine, showing the structure of the organic product.
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(i) C4H8 + Br2 ? C4H8Br2; Equation scores [1]. CH3CHBrCHBrCH3; 2 Accept more detailed formula.
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(ii) State the type of reaction occurring.
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addition
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CH3COCH3 can be prepared in the laboratory from an alcohol. State the name of this alcohol, the type of reaction occurring and the reagents and conditions needed for the reaction.
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propan-2-ol; Accept 2-propanol. oxidation/redox; (potassium/sodium) dichromate(VI)/potassium manganate(VII); Accept just dichromate, permanganate, KMnO4 , Mn, K2Cr2O7, Cr2 (sulfuric) acid; heat under reflux;

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