14.1. Alkanes
A subsection of Chemistry, 9701, through 14. Hydrocarbons
Listing 10 of 122 questions
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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Hexane, C6H14, is a colourless liquid. Two test-tubes contain equal amounts of hexane. 1 cm3 of bromine, Br2, is added to both test‑tubes. One test-tube is kept in the dark and the other is exposed to sunlight. The table describes the appearance of each test-tube after one hour. test-tube conditions observations in the dark no change, mixture remains orange in sunlight colour of mixture fades to pale yellow The test-tube in the dark is kept cool and is not exposed to ultraviolet light. Explain the observations for the test-tube kept in the dark. In sunlight, bromine reacts with hexane by a mechanism which occurs via a series of steps. State the name of the mechanism of the reaction that occurs. Give an equation which shows a propagation step in this reaction in which hexane produces •C6H13. Give an equation which shows a propagation step in this reaction that produces 1-bromohexane. Give an equation which shows a termination step in this reaction that produces 1-bromohexane. A and B are different straight chain alkenes with molecular formula, C6H12. A does not show stereoisomerism. A reacts with potassiummanganate(to form hexane-1,2-diol. Draw the structural formula of A.  State the conditions needed for this reaction of A. B reacts with hydrogen gas in the presence of a platinum catalyst to produce hexane. Name the type of reaction occurring. In terms of σ and π bonds, describe any similarities and differences in the type of carbon‑carbon bonds in B and the type of carbon‑carbon bonds in hexane. 
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THEORY
2020
Paper 2, Variant 3
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Naphtha is a mixture which contains only hydrocarbon molecules. What is meant by the term hydrocarbon? Name the raw material that is used to produce a sample of naphtha. CompoundV is found in naphtha. It has a molecular formula C10H22. When V is heated at high pressure in the absence of air, an equal number of moles of ethene, propene and W are made. W is a compound made of straight chain, saturated molecules. Name the process that describes this reaction. Deduce the structure of W. Draw its structure below.  Propene is separated from the mixture and heated in air in the presence of a catalyst. Propene is oxidised to X, which contains two functional groups. Effervescence is seen when Na2CO3is added to X. Identify the functional group present in X which is responsible for this observation. Identify a reagent which could be used to show that X contains a C=C. Include relevant observations. X reacts with another reagent to form Y. Molecules of Y react together to form addition polymerZ. The diagram shows the repeat unit of polymerZ. O O– Na+ repeat unit of polymer Z Draw the structural formula of monomerY.  Polymer Z is useful because it absorbs large amounts of water. However, there are problems associated with the disposal of products containing polymer Z. Combustion is not an appropriate method to dispose of pure Z because the process releases harmful gases. Some of these gases contribute to the enhanced greenhouse effect. Identify a gas released during the combustion of Z which contributes to the enhanced greenhouse effect. Identify another gas which could be produced during the combustion of pure Z. Describe a consequence, other than the enhanced greenhouse effect, of its release into the atmosphere. gas consequence  
9701_s21_qp_21
THEORY
2021
Paper 2, Variant 1
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V is a colourless liquid. V HO O V reacts with an excess of LiAl H4 to form W. Draw the structure of W in the box. W Identify the role of LiAl H4 in the reaction with V. V reacts to form Z in a single reaction, as shown in . V HO O Z HO O OH OH Suggest the reagent and conditions needed to form Z from V. Deduce the empirical formula of Z. Complete Table 4.1 to show the number of sp2 and sp3 hybridised carbon atoms that are present in a molecule of V. Table 4.1 type of hybridisation sp2 sp3 number of carbon atoms in V Q contains the elements carbon, hydrogen and oxygen only. It is a saturated molecule with no branching in its carbon backbone. Q contains only one functional group. The relative molecular mass of Q is 88. No effervescence is seen when Na2CO3 is added to Q. Effervescence is seen when sodium is added to Q. Q reacts with alkaline I2to form a yellow precipitate. Draw the structure of Q in the box. Q
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THEORY
2023
Paper 2, Variant 1
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Questions Discovered
122