14.1. Alkanes
A subsection of Chemistry, 9701, through 14. Hydrocarbons
Listing 10 of 122 questions
Alkanes are generally considered to be unreactive compounds, showing an inertness to common reagents such as NaOH, H2SO4, and K2Cr2O7. Suggest a reason why these reagents do not attack an alkane such as CH4. When a mixture of chlorine and ethane gas is exposed to strong sunlight, an explosion can occur due to the fast exothermic reaction. Under more controlled conditions, however, the following reaction occurs. C2H6 + Cl2 C2H5Cl + HCl What is the name of this type of reaction? Use equations to describe the mechanism of this reaction, naming the steps involved. This reaction can produce organic by-products, in addition to C2H5Cl. Draw the structural formulae of three possible organic by-products. Two of your by-products should contain 4 carbon atoms per molecule. Briefly describe how each by-product could be formed. structural formula of by-product formed by It is found by experiment that, during this type of reaction, primary, secondary and tertiary hydrogen atoms are replaced by chlorine atoms at different rates, as shown in the following table. reaction relative rate RCH3 RCH2Cl R2CH2 R2CHCl R3CH R3CCl Using this information, and considering the number of hydrogen atoms of each type (primary, secondary or tertiary) within the molecule, predict the relative ratio of the two possible products J and K from the chlorination of 2-methylpropane. Explain your answer. H3C CH3 CH3 CH H3C CH3 CH3 + C Cl H3C CH3 CH2 CH 2-methylpropane J K Cl ratio J / K = explanation: In the boxes below draw the skeletal formulae of four different structural isomers of C5H11Cl that could be obtained from the chlorination of 2-methylbutane. Indicate any chiral centres in your structures by an asterisk (*). C5H11Cl + HCl + Cl2 2-methylbutane
9701_w11_qp_43
THEORY
2011
Paper 4, Variant 3
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Crude oil is a mixture of many hydrocarbons ranging in size from 1 to 40 carbon atoms per molecule. The alkanes in crude oil can be separated because they have different boiling points. The table below shows the boiling points of some alkanes. alkane boiling point / °C Mr butane pentane hexane 2-methylbutane dimethylpropane 2,3-dimethylbutane What is the correct explanation for the difference in the boiling points of the three isomers with Mr = 72?
9701_w15_qp_11
MCQ
2015
Paper 1, Variant 1
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Crude oil is a mixture of many hydrocarbons ranging in size from 1 to 40 carbon atoms per molecule. The alkanes in crude oil can be separated because they have different boiling points. The table below shows the boiling points of some alkanes. alkane boiling point / °C Mr butane pentane hexane 2-methylbutane dimethylpropane 2,3-dimethylbutane What is the correct explanation for the difference in the boiling points of the three isomers with Mr = 72?
9701_w15_qp_13
MCQ
2015
Paper 1, Variant 3
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In each section of this question choose the answer or answers from the options listed. Six particles are listed. H• H+ Cl • Cl – •CH3 +CH3 Identify two particles produced during the reaction of methane and chlorine in the presence of UVlight. Identify the two particles produced by the heterolytic fission of a bond in chloromethane. Seven reaction types are listed. addition substitution oxidation elimination hydrolysis condensation reduction Name the type of reaction involved when Tollens’ reagent is used to identify an aldehyde. Name the type of reaction involved in the test for a carbonyl group using 2,4-DNPH. Name the type of reaction involved in the reaction of a ketone with NaBH4. Name the type of reaction involved in the reaction of an aldehyde with HCN.
9701_w16_qp_22
THEORY
2016
Paper 2, Variant 2
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An alkene, a carboxylic acid and a ketone, all of similar volatility, are mixed together. The mixture is then analysed by gas chromatography. The gas chromatogram produced is shown. absorption time / mins J K L The separation of the three compounds depends on their relative solubilities in the liquid stationary phase. The liquid stationary phase is an alkane. Complete the table to suggest which compound in the mixture is responsible for each peak J, K and L. Explain your answer by reference to the intermolecular forces of each compound. peak organic compound explanation J K L  A student calculates the areas underneath the three peaks in the chromatogram. peak J K L area / mm2 The area underneath each peak is proportional to the mass of the respective compound. Calculate the percentage by mass in the original mixture of the compound responsible for peak K.  % of mixture responsible for peak K = Chlorobenzene can be prepared from benzene as shown. Cl 2 Cl Al Cl 3 Aluminium chloride, Al Cl 3, catalyses this reaction. Write an equation to show how Al Cl 3 generates the electrophile needed in this reaction. Draw the mechanism of the reaction between this electrophile and benzene to form chlorobenzene. Include all relevant curly arrows and charges.  Write an equation to show how the catalyst is regenerated. Catalysts can be heterogeneous or homogeneous. Explain what is meant by a homogeneous catalyst. Complete the table by placing one tick () in each row to indicate the mode of action of the catalyst in each reaction. heterogeneous homogeneous Rh in the removal of NO2 from exhaust gases of cars Fe3+ in the I – / S2O8 2– reaction  
9701_w18_qp_42
THEORY
2018
Paper 4, Variant 2
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Questions Discovered
122