AQA Jun 2016 Paper 4 Q2

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do not write outside the box hemiacetals and acetals are compounds formed by the reaction of aldehydes with alcohols such as the reaction of ethanal with ethanol ch cho ch ch oh h c oh och ch a hemiacetal a i use your knowledge of carbonyl mechanisms to suggest the name of the mechanism of this reaction mark a ii outline how an ethanol molecule reacts with an ethanal molecule in the first step of this mechanism include two curly arrows to show the movement of electron pairs marks b the reaction produces a racemic mixture of chiral molecules b i explain the meaning of the term racemic mixture mark b ii state the relationship between two chiral molecules with the same structural formula mark turn over wmp jun chem do not write outside the box c in the presence of an acid catalyst such as dry hydrogen chloride ethanal reacts with an excess of ethanol to form an acetal the overall reaction of ethanal with an excess of ethanol forms an equilibrium mixture as shown all reactants and products are liquids ch cho ch ch oh h c och ch och ch an acetal h o a mixture of mol of ethanal and mol of ethanol was left to reach equilibrium in the presence of dry hydrogen chloride at a given temperature the equilibrium mixture contained mol of the acetal c i calculate the amount in moles of ethanal and of ethanol in this equilibrium mixture marks amount of ethanal mol amount of ethanol mol space for working wmp jun chem do not write outside the box c ii in a different experiment using the same reaction as in part c an equilibrium mixture was established at a given temperature this mixture contained mol of ethanal mol of ethanol mol of the acetal and mol of water in a total volume of cm write an expression for the equilibrium constant kc for this reaction calculate a value for kc at this temperature give units with your answer marks kc calculation d draw the structure of the acetal c h o formed by the reaction of ethanal with ethane diol mark turn over wmp jun chem

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