14.1. Alkanes
A subsection of Chemistry, 9701, through 14. Hydrocarbons
Listing 10 of 122 questions
Octadecane, C18H38, is a long chain hydrocarbon which is present in crude oil. Such long chain hydrocarbons are ‘cracked’ to produce alkanes and alkenes which have smaller molecules. Give two different conditions under which long chain molecules may be cracked. Octadecane, C18H38, can be cracked to form hexane and an alkene. Write a balanced equation for this reaction. Alkenes are important industrially because the C=C bond makes them very reactive. Ethene reacts with bromine to give 1,2-dibromoethane. What type of reaction is this? Outline the mechanism of this reaction, giving the structure of the intermediate. Show clearly any relevant dipoles, charges and lone pairs of electrons. = C C H H H H C C H H H H Br Br Br Br The unsaturated hydrocarbon Z is obtained by cracking hexane and is important in the chemical industry. The standard enthalpy change of combustion of Z is –2059 kJ mol–1. Define the term standard enthalpy change of combustion. When 0.47 g of Z were completely burnt in air, the heat produced raised the temperature of 200 g of water by 27.5 °C. Calculate the amount of heat released in this experiment. Use the data above and your answer to to calculate the relative molecular mass of Z. Deduce the molecular formula of Z. The unsaturated hydrocarbon Z can be polymerised. Draw the structure of the polymer of Z showing two repeat units.
9701_w06_qp_2
THEORY
2006
Paper 2, Variant 0
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Ketene, C2H2O, is a member of a class of unsaturated organic compounds that is widely used in pharmaceutical research for the synthesis of organic compounds. CH2=C=O ketene Suggest values for the H-C-H and C=C=O bond angles in ketene. H-C-H …………………………………… C=C=O …………………………………… By considering the structure of the molecule, suggest why the name ketene is used. Ketene burns completely in air to form carbon dioxide and water. Write a balanced equation for this reaction. Use your equation to calculate the volume of CO2, in dm3, measured at room temperature and pressure, which will be formed when 3.5g of ketene are burned in an excess of air. Give your answer to two significant figures. volume of CO2 = dm3 Define the term standard enthalpy change of formation. Use the data below to calculate the standard enthalpy change of formation of ketene. ∆H o/kJ mol–1 standard enthalpy change of formation of CO2 –395 standard enthalpy change of combustion of H2 –286 standard enthalpy change of combustion of CH2=C=O –1028 Ketene can be converted directly into ethanoic acid, CH3CO2H, by reaction with a compound A. Suggest the identity of A. ………………
9701_w08_qp_2
THEORY
2008
Paper 2, Variant 0
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Use The viscosity of engine oil can be improved by the addition of certain medium chain- length polymers. A portion of the chain of one such polymer is shown below. –CH2CH(CH2CH2CH3)CH2CH(CH2CH2CH3)CH2– On average, the molecules of the medium-chain polymer contain 40 carbon atoms. Suggest the structure of the monomer. How many monomer units are incorporated into the average molecule of the polymer? Used car engine oil can be recycled for use as a fuel by the processes of distillation and cracking. Assuming a typical molecule of engine oil has the formula C40H82, suggest an equation for a cracking reaction that could produce diesel fuel with the formula C16H34 and other hydrocarbons only. What conditions are needed for this cracking reaction? Considering only the bonds broken and the bonds formed during the reaction, use the Data Booklet to calculate the enthalpy change for the reaction you wrote in . Comment on how the conditions you described in relate to the enthalpy change you calculated in .
9701_w08_qp_4
THEORY
2008
Paper 4, Variant 0
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Crude oil is a naturally occurring flammable liquid which consists of a complex mixture of hydrocarbons. In order to separate the hydrocarbons the crude oil is subjected to fractional distillation. Explain what is meant by the following terms. hydrocarbon fractional distillation Undecane, C11H24, is a long chain hydrocarbon which is present in crude oil. Such long chain hydrocarbons are ‘cracked’ to produce alkanes and alkenes which have smaller molecules. Give the conditions for two different processes by which long chain molecules may be cracked. process 1 process 2 Undecane, C11H24, can be cracked to form pentane, C5H12, and an alkene. Construct a balanced equation for this reaction. Pentane, C5H12, exhibits structural isomerism. Draw the three structural isomers of pentane. isomer B isomer C isomer D The three isomers of pentane have different boiling points. Which of your isomers has the highest boiling point? isomer Suggest an explanation for your answer. The unsaturated hydrocarbon, E, is obtained by cracking hexane and is important in the chemical industry. The standard enthalpy change of combustion of E is –2059 kJ mol–1. Define the term standard enthalpy change of combustion. When 0.47 g of E was completely burnt in air, the heat produced raised the temperature of 200 g of water by 27.5 °C. Assume no heat losses occurred during this experiment. Use relevant data from the Data Booklet to calculate the amount of heat released in this experiment. Use the data above and your answer to to calculate the relative molecular mass, Mr, of E. Deduce the molecular formula of E.
9701_w10_qp_21
THEORY
2010
Paper 2, Variant 1
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Crude oil is a naturally occurring flammable liquid which consists of a complex mixture of hydrocarbons. In order to separate the hydrocarbons the crude oil is subjected to fractional distillation. Explain what is meant by the following terms. hydrocarbon fractional distillation Undecane, C11H24, is a long chain hydrocarbon which is present in crude oil. Such long chain hydrocarbons are ‘cracked’ to produce alkanes and alkenes which have smaller molecules. Give the conditions for two different processes by which long chain molecules may be cracked. process 1 process 2 Undecane, C11H24, can be cracked to form pentane, C5H12, and an alkene. Construct a balanced equation for this reaction. Pentane, C5H12, exhibits structural isomerism. Draw the three structural isomers of pentane. isomer B isomer C isomer D The three isomers of pentane have different boiling points. Which of your isomers has the highest boiling point? isomer Suggest an explanation for your answer. The unsaturated hydrocarbon, E, is obtained by cracking hexane and is important in the chemical industry. The standard enthalpy change of combustion of E is –2059 kJ mol–1. Define the term standard enthalpy change of combustion. When 0.47 g of E was completely burnt in air, the heat produced raised the temperature of 200 g of water by 27.5 °C. Assume no heat losses occurred during this experiment. Use relevant data from the Data Booklet to calculate the amount of heat released in this experiment. Use the data above and your answer to to calculate the relative molecular mass, Mr, of E. Deduce the molecular formula of E.
9701_w10_qp_22
THEORY
2010
Paper 2, Variant 2
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Questions Discovered
122