14. Hydrocarbons
A section of Chemistry, 9701
Listing 10 of 313 questions
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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The following scheme outlines the production of some compounds from ethene. Br H2C CH2 I Br HO2C CO2H H2N NH2 A B C (C4H4N2) E F D II III SOCl2 KCN, heat in ethanol excess of NH3, heat in ethanol under pressure Suggest the reagent and conditions for reaction I. Describe the mechanism of reaction I by means of a diagram. Include all whole, partial and induced charges, and represent the movements of electron pairs by curly arrows. Suggest the identities of compounds B, C and E, and draw their structures in the boxes opposite. Suggest reagents and conditions for reaction II, reaction III. During reaction II the nitrogen atoms are lost from the organic molecule. Suggest the identity of the nitrogen-containing ion produced during this reaction. Compounds E and F react together to give a polymer and an inorganic product. Draw one repeat unit of this polymer. Identify the inorganic product. A 0.100 mol dm–3 solution of compound D has a pH of 2.60. Calculate the [H+] in this solution. Hence calculate the value of Ka of compound D.
9701_w10_qp_43
THEORY
2010
Paper 4, Variant 3
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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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Questions Discovered
313