OCR A Jun 2010 Paper 2 Q1

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Answer all the questions. The alkanes are an homologous series of hydrocarbons. The table shows information about some straight chain alkanes. alkane molecular formula boiling point / C methane ethane propane butane CH4 C2H6 C3H8 C4H10 1648942 1 (a) (i) What is meant by an homologous series?[1] (ii) Explain why the boiling points increase down the alkane homologous series.[2]OCR 2010<br />
 (b) Alkynes are another homologous series of hydrocarbons. The table gives the molecular formulae of the first five straight chain alkynes. alkyne molecular formula ethyne propyne but-1-yne hex-1-yne C2H2 C3H4 C4H6 C5H8 C6H10 (i) Suggest the name of a straight chain alkyne with the molecular formula C5H8.[1] (ii) Deduce the general formula for an alkyne.[1] (iii) The alkynes contain the C C functional group. Suggest the displayed formula for propyne. (iv) Hex-1-yne has many cyclic structural isomers. Draw the skeletal structure of one of these cyclic structural isomers. [1] [1]OCR 2010 Turn over<br />
 (c) Ethyne is commonly called acetylene. It is used in an oxy-acetylene flame which is hot enough to cut through steel. Ethyne completely combusts as shown in the equation below. 2 O O2 Calculate the enthalpy change of combustion of ethyne using the average bond enthalpies in the table below. bond CH C C O=O C=O OH average bond enthalpy / kJ mol1 +415 +837 +498 +805 +464 enthalpy change of combustion =kJ mol1 [3]OCR 2010<br />
 (d) Ethyne is formed when water reacts with calcium carbide, CaC2. CaC2(s) + 2H2O(l) Ca(OH)2(s) + C2H2(g) The standard enthalpy change of this reaction can be determined indirectly using standard enthalpy changes of formation. (i) What is meant by the term standard enthalpy change of formation, Hf You should state the standard conditions in your answer. O ?[3] (ii) Standard enthalpy changes of formation are shown in the table below. substance CaC2(s) H2O(l) Ca(OH)2(s) C2H2(g) standard enthalpy change O / kJ mol1 of formation, Hf60 286 987 +227 Calculate the standard enthalpy change of the reaction: CaC2(s) + 2H2O(l) Ca(OH)2(s) + C2H2(g) standard enthalpy change of reaction = . kJ mol1 [3]OCR 2010 Turn over<br />
 (e) A factory makes ethyne gas from calcium carbide, CaC2. One of the waste products is calcium hydroxide. CaC2 + 2H2O Ca(OH)2 + C2H2 Each day 1.00106 grams of calcium carbide are used and 3.60105 dm3 of ethyne gas, measured at room temperature and pressure, is manufactured. (i) Calculate the atom economy for this process using the relative formula masses in the table below. compound relative formula mass CaC2 H2O Ca(OH)2 C2H2 64.1 18.0 74.1 26.0 (ii) Calculate the amount, in moles, of CaC2 used each day. atom economy =% [2] (iii) Calculate the amount, in moles, of C2H2 made each day. amount of CaC2 = mol [1] (iv) Calculate the percentage yield of C2H2. amount of C2H2 = mol [1]OCR 2010 percentage yield = . % [1]<br />
 (v) Comment on the percentage yield and the atom economy of this process in terms of sustainability.[2] [Total: 23]OCR 2010 Turn over<br />

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