14. Hydrocarbons
A section of Chemistry, 9701
Listing 10 of 313 questions
Crude oil is a complex mixture of hydrocarbon molecules. The hydrocarbon molecules in crude oil are separated by fractional distillation. Fractional distillation is used because the different hydrocarbon molecules in crude oil have different boiling points. Explain why the hydrocarbon molecules in crude oil have different boiling points. Some of the hydrocarbon molecules obtained from crude oil are processed further by cracking. Suggest why some hydrocarbon molecules are processed further by cracking. Cracking one mole of dodecane, C12H26, produces two moles of ethene and one mole of another hydrocarbon molecule. Write the equation for this cracking reaction. The ethene can be used in the production of poly. Give the full name of the process used to produce polyfrom ethene. Give two reasons why polyshould be reused or recycled rather than just thrown away. Part of a polymer chain, produced by the same type of process as poly, is shown. CH2 CH3 C COOCH3 CH2 CH3 C COOCH3 CH2 CH3 C COOCH3 Give the displayed formula of the monomer used to produce this polymer.  
9701_s18_qp_21
THEORY
2018
Paper 2, Variant 1
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There are many different types of aliphatic and aromatic hydrocarbons. Name a naturally occurring source of aliphatic and aromatic hydrocarbons and outline how different hydrocarbons are separated from this source. name of source outline of separation of hydrocarbons  When alkanes are heated to high temperatures, in the absence of air, the molecules can break into smaller molecules. Identify the type of reaction occurring. Write an equation which describes the reaction occurring when heptane, C7H16, is heated in the absence of air, to form hexane, butane and ethene only. The equation for the complete combustion of ethene is shown. C2H4 + 3O2 2CO2 + 2H2O Calculate the volume, in dm3, of carbon dioxide formed in the complete combustion of 1.00 g of ethene at room temperature and pressure.  volume of CO2 = dm3 The table compares the reactivity of alkanes and alkenes with chlorine. alkanes alkenes name of the type of reaction with chlorine substitution addition and substitution name of the type of reacting species free radical electrophile and free radical During the first stage in the substitution reaction chlorine forms chlorine free radicals. Explain what is meant by the term free radical. Name and explain the type of bond breaking which occurs to form chlorine free radicals. Name the stage of the reaction mechanism which occurs when a methane molecule reacts with a chlorine free radical. Complete the equation for the reaction which occurs when a methane molecule reacts with a chlorine free radical. C H H H + + •Cl H  Carbon atoms can form σ and π bonds within hydrocarbon molecules. Explain the following statement with reference to σ and π bonds. Alkenes react with electrophiles but alkanes do not. 
9701_s19_qp_22
THEORY
2019
Paper 2, Variant 2
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Three alkenes, X, Y and Z, have the same molecular formula. Describe what is seen when aqueousbromine is added to X. X, Y and Z are reacted separately with hot, concentrated, acidified manganate(ions until no further reaction occurs. The carbon-containing products are shown in the table. alkene carbon-containing products X CO2 + (CH3)2CO Y CO2 + CH3CH2CO2H Z CH3CO2H Draw the structures of X, Y and Z. X Y Z  Deduce the molecular formula of X, Y and Z. The structures of V and W are shown. CH3(CH2)2CH2OH (CH3)3COH V W Name the class of compound that V and W each belong to. V W  V and W both react with sodium metal. Write an equation for the reaction of V with sodium metal. Name a reagent used to distinguish V from W. Describe any observations. reagent observations with V observations with W  
9701_s19_qp_23
THEORY
2019
Paper 2, Variant 3
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Benzene can be converted into cyclohexane. For this reaction name the type of reaction and identify the reagent and conditions needed. type of reaction reagent and conditions  State the bond angles in benzene and cyclohexane. bond angle in benzene bond angle in cyclohexane Explain your answers.  When benzene reacts with SO3, benzenesulfonic acid is produced. SO3H benzenesulfonic acid + SO3 The mechanism of this reaction is similar to that of the nitration of benzene. Concentrated H2SO4 is used in an initial step to generate the SO3H+ electrophile as shown. SO3 + H2SO4 SO3H+ + HSO4 – Draw a mechanism for the reaction of benzene with SO3H+ ions. Include all necessary curly arrows and charges. SO3H benzenesulfonic acid SO3H+  Write an equation to show how the H2SO4 catalyst is reformed. 3-dodecylbenzenesulfonic acid can be prepared from benzenesulfonic acid. 3-dodecylbenzenesulfonic acid SO3H SO3H C12H25 benzenesulfonic acid Suggest the reagents and conditions and name the mechanism for this reaction. reagents and conditions mechanism  When concentrated sulfuricacid is added to water, dissociation takes place in two stages. stage 1 H2SO4 H+ + HSO4 – stage 2 HSO4 – H+ + SO4 2– Ka2 = 1.0 × 10–2 mol dm–3 Ka2 is the acid dissociation constant for stage 2. Write the expression for the acid dissociation constant Ka2. Ka2 =  H2SO4 is considered a strong acid whereas HSO4 – is considered a weak acid. Suggest how the magnitude of the acid dissociation constant for stage1 compares to Ka2. Benzoic acid, C6H5CO2H, is a weak acid. A solution of 0.0250 mol dm–3 benzoic acid has a pH of 2.90. Calculate the Ka of benzoic acid.  Ka = mol dm–3  
9701_s19_qp_41
THEORY
2019
Paper 4, Variant 1
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By reference to the formation of σ and π bonds, describe and explain the shape of a benzene molecule, C6H6. 2,3-dimethylphenylamine can be prepared from 1,2-dimethylbenzene in two steps as shown. 1,2-dimethylbenzene CH3 CH3 M CH3 CH3 NO2 2,3-dimethylphenylamine CH3 CH3 NH2 HNO3 / H2SO4 step 1 step 2 Step1 is catalysed by H2SO4. Write an equation to show how H2SO4 generates the electrophile during step1. Draw the mechanism of the reaction between this electrophile and 1,2-dimethylbenzene to form M. Include all relevant curly arrows and charges. intermediate CH3 CH3 M CH3 CH3 NO2  Write an equation to show how the H2SO4 catalyst is reformed. For step2, suggest the reagents and conditions and name the type of reaction. ● reagents and conditions ● type of reaction  The drug mefenamic acid can be made using 2,3-dimethylphenylamine in an excess of 2‑chlorobenzoic acid. 2,3-dimethylphenylamine CH3 CH3 2-chlorobenzoic acid mefenamic acid CO2H CO2H Cl + + HCl NH2 CH3 CH3 N H Deduce the molecular formula of mefenamic acid. Name the functional groups, apart from the benzene ring, in mefenamic acid. Calculate the maximum mass of mefenamic acid that could be formed from 5.00 g of 2,3‑dimethylphenylamine in this reaction. Give your answer to three significant figures.  mass of mefenamic acid = g The position of substitution in the electrophilic substitution of arenes can be explained based on the stability of the intermediate cations formed in the first step. The example given involves the bromination of methylbenzene. methylbenzene CH3 CH3 + CH3 3-position 2-position 4-position Br H Br H CH3 + + Br H Use this information and your knowledge about the stability of cations to suggest why the CH3 group directs incoming electrophiles to the 2- and 4-positions in preference to the 3-position. 
9701_s19_qp_42
THEORY
2019
Paper 4, Variant 2
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Benzene can be converted into cyclohexane. For this reaction name the type of reaction and identify the reagent and conditions needed. type of reaction reagent and conditions  State the bond angles in benzene and cyclohexane. bond angle in benzene bond angle in cyclohexane Explain your answers.  When benzene reacts with SO3, benzenesulfonic acid is produced. SO3H benzenesulfonic acid + SO3 The mechanism of this reaction is similar to that of the nitration of benzene. Concentrated H2SO4 is used in an initial step to generate the SO3H+ electrophile as shown. SO3 + H2SO4 SO3H+ + HSO4 – Draw a mechanism for the reaction of benzene with SO3H+ ions. Include all necessary curly arrows and charges. SO3H benzenesulfonic acid SO3H+  Write an equation to show how the H2SO4 catalyst is reformed. 3-dodecylbenzenesulfonic acid can be prepared from benzenesulfonic acid. 3-dodecylbenzenesulfonic acid SO3H SO3H C12H25 benzenesulfonic acid Suggest the reagents and conditions and name the mechanism for this reaction. reagents and conditions mechanism  When concentrated sulfuricacid is added to water, dissociation takes place in two stages. stage 1 H2SO4 H+ + HSO4 – stage 2 HSO4 – H+ + SO4 2– Ka2 = 1.0 × 10–2 mol dm–3 Ka2 is the acid dissociation constant for stage 2. Write the expression for the acid dissociation constant Ka2. Ka2 =  H2SO4 is considered a strong acid whereas HSO4 – is considered a weak acid. Suggest how the magnitude of the acid dissociation constant for stage1 compares to Ka2. Benzoic acid, C6H5CO2H, is a weak acid. A solution of 0.0250 mol dm–3 benzoic acid has a pH of 2.90. Calculate the Ka of benzoic acid.  Ka = mol dm–3  
9701_s19_qp_43
THEORY
2019
Paper 4, Variant 3
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