AQA Jun 2010 Paper 2 Q2

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do not write outside the box a a student carried out an experiment to study the rates of hydrolysis of some haloalkanes in the experiment two different haloalkanes were placed in separate test tubes containing silver nitrate solution the haloalkanes reacted with the water in the silver nitrate solution the student timed how long it took for the first appearance of the silver halide precipitate in each tube at a constant temperature this time was used to provide a measure of the initial rate of reaction the student obtained the following results time to form a precipitate s bromobutane iodobutane a i state the meaning of the term hydrolysis mark a ii state the colour of the precipitate formed when iodide ions react with silver nitrate and write the simplest ionic equation for this reaction colour of precipitate simplest ionic equation marks a iii use your knowledge of the reactions of halide ions with silver nitrate to suggest why the student did not include fluorobutane in this experiment marks wmp jun chem do not write outside the box b the student used the following enthalpy data to try to account for the different initial rates of hydrolysis of the haloalkanes used in part a the student deduced that the rate of hydrolysis of a haloalkane is influenced by the strength of the carbon halogen bond in the haloalkane bond enthalpy kj mol c br c i state how the experimental evidence enabled the student to make this deduction mark c the student had read that the reaction of water with haloalkanes was similar to the reaction of aqueous sodium hydroxide with haloalkanes and was an example of a nucleophilic substitution reaction c i state the meaning of the term nucleophile mark c ii when a hydroxide ion collides with a molecule of bromobutane the following reaction occurs ch ch ch ch br oh ch ch ch ch oh br outline the nucleophilic substitution mechanism for this reaction question continues on the next page marks turn over wmp jun chem do not write outside the box d the reaction of hydroxide ions with bromo methylpropane may occur by a different mechanism from the one in part c this different mechanism involves the formation of a carbocation d i complete the following equation by drawing the structure of the carbocation formed when the c br bond in bromo methylpropane is broken ch ch c br ch br mark d ii suggest one reason why this reaction occurs by a mechanism involving a carbocation but the reaction in part c ii does not mark wmp jun chem

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