1 Optical isomerism

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Oxford Textbook Pages : 401 - 407

CGP Revision Guide Pages : 160 - 161

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Show Specification Ref : 3.3.7

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Question 1 / 5

June 2011 QP – Unit 2 AQA Chemistry A-level_question_8 section b answer all questions in the spaces provided do not write outside the box a some scientists thought that the waste water from a waste disposal factory contained two sodium halides they tested a sample of the waste water they added three reagents one after the other to the same test tube containing the waste water the table below shows their results reagent added observations silver nitrate solution acidified with dilute nitric acid a cream precipitate formed dilute ammonia solution a yellow precipitate remained concentrated ammonia solution the yellow precipitate did not dissolve a i identify the yellow precipitate that did not dissolve in concentrated ammonia solution write the simplest ionic equation for the formation of this precipitate from silver ions and the correct halide ion identify the other sodium halide that must be present in this mixture of two sodium halides marks a ii give one reason why the silver nitrate solution was acidified before it was used in this test mark wmp jun chem do not write outside the box a iii the method that the scientists used could not detect one type of halide ion identify this halide ion give one reason for your answer marks b the scientists thought that the waste water also contained dissolved barium ions an aqueous solution of sodium sulfate can be used to test for the presence of dissolved barium ions write the simplest ionic equation for the reaction between barium ions and sulfate ions to form barium sulfate state what is observed in this reaction give a use for barium sulfate in medicine and explain why this use is possible given that solutions containing barium ions are poisonous marks question continues on the next page turn over wmp jun chem do not write outside the box the scientists also analysed the exhaust gases from an incinerator used to destroy waste poly ethene mass spectrometry showed that there was a trace gas with a precise mr in the exhaust gases from the incinerator the table below contains some precise relative atomic mass data atom precise relative atomic mass c h o use the data to show that the trace gas is ethene show your working suggest why both ethene and carbon monoxide might have been identified as the trace gas if the scientists had used relative atomic masses to a precision of only one decimal place write an equation for the incomplete combustion of ethene to form carbon monoxide and water only ethene is used to make poly ethene draw the displayed formula for the repeating unit of poly ethene name this type of polymer marks wmp jun chem c
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Question 2 / 5

June 2013 QP – Unit 2 AQA Chemistry A-level_question_1 section a answer all questions in the spaces provided do not write outside the box sulfuric acid is manufactured by the contact process a in this process sulfur dioxide reacts with oxygen the equation for the equilibrium that is established is so g o g so g h kj mol a i state and explain the effect of a decrease in temperature on the equilibrium yield of so effect of a decrease in temperature on yield explanation marks extra space a ii give two features of a reaction at equilibrium feature feature marks question continues on the next page turn over wmp jun chem b write an equation for the reaction of concentrated sulfuric acid with potassium bromide to form potassium hydrogensulfate and hydrogen bromide do not write outside the box mark c bromine is one of the products formed when concentrated sulfuric acid reacts with hydrogen bromide write an equation for this reaction state the role of sulfuric acid in this reaction equation role of sulfuric acid marks d concentrated sulfuric acid is used in a two stage process to convert methylpropene into methylpropan ol stage ch c ch h so ch c oso oh ch stage ch c oso oh ch h o ch c oh ch h so d i name and outline a mechanism for stage of this conversion name of mechanism mechanism marks wmp jun chem d ii deduce the type of reaction in stage of this conversion mark d iii state the overall role of sulfuric acid in this conversion mark do not write outside the box turn over for the next question turn over wmp jun chem
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Question 3 / 5

June 2014 QP – Unit 2 AQA Chemistry A-level_question_7 do not write outside the box table gives the names and structures of some structural isomers with the molecular formula c h table name of isomer structure isomer pent ene ch ch chch ch isomer cyclopentane isomer methylbut ene ch chch ch isomer methylbut ene ch c chch isomer methylbut ene h c c ch ch ch a isomer exists as e and z stereoisomers a i state the meaning of the term stereoisomers marks a ii draw the structure of the e stereoisomer of isomer mark wmp jun chem do not write outside the box b a chemical test can be used to distinguish between separate samples of isomer and isomer identify a suitable reagent for the test state what you would observe with isomer and with isomer marks reagent observation with isomer observation with isomer c use table a on the data sheet when answering this question isomer and isomer have similar structures c i state the infrared absorption range that shows that isomer and isomer contain the same functional group mark c ii state one way that the infrared spectrum of isomer is different from the infrared spectrum of isomer mark question continues on the next page turn over wmp jun chem do not write outside the box d two alcohols are formed by the hydration of isomer draw the displayed formula for the alcohol formed that is oxidised readily by acidified potassium dichromate vi mark e isomer reacts with hydrogen bromide to give two structurally isomeric bromoalkanes e i name and outline a mechanism for the reaction of isomer with hydrogen bromide to give bromo methylbutane as the major product marks ch c chch hbr ch cbrch ch name of mechanism mechanism wmp jun chem do not write outside the box e ii the minor product in this reaction mixture is bromo methylbutane explain why this bromoalkane is formed as a minor product marks f name and outline a mechanism for the following reaction to form isomer state the role of the hydroxide ion in this reaction marks ch cbrch ch koh h c c ch ch ch kbr h o name of mechanism mechanism role of hydroxide ion turn over wmp jun chem
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Question 4 / 5

January 2011 QP – Unit 4 AQA Chemistry A-level_question_5 do not write outside the box atenolol is an example of the type of medicine called a beta blocker these medicines are used to lower blood pressure by slowing the heart rate the structure of atenolol is shown below ch h n oh ch ch ch p ch ch ch q a give the name of each of the circled functional groups labelled j and k on the structure of atenolol shown above functional group labelled j functional group labelled k marks b the h n m r spectrum of atenolol was recorded one of the peaks in the h n m r spectrum is produced by the ch group labelled p in the structure of atenolol use table on the data sheet to suggest a range of values for this peak name the splitting pattern of this peak range of values name of splitting pattern marks c n m r spectra are recorded using samples in solution the h n m r spectrum was recorded using a solution of atenolol in cdcl c i suggest why cdcl and not chcl was used as the solvent mark c ii suggest why cdcl is a more effective solvent than ccl for polar molecules such as atenolol mark wmp jan chem do not write outside the box d the c n m r spectrum of atenolol was also recorded use the structure of atenolol given to deduce the total number of peaks in the c n m r spectrum of atenolol e mark part of the c n m r spectrum of atenolol is shown below use this spectrum and table on the data sheet where appropriate to answer the questions which follow ppm e i give the formula of the compound that is used as a standard and produces the peak at ppm in the spectrum mark e ii one of the peaks in the c n m r spectrum above is produced by the ch group labelled q in the structure of atenolol identify this peak in the spectrum by stating its value mark e iii there are three ch groups in the structure of atenolol one of these ch groups produces the peak at in the c n m r spectrum above draw a circle around this ch group in the structure of atenolol shown below ch ch oh ch ch ch ch ch h n question continues on the next page mark turn over wmp jan chem do not write outside the box f atenolol is produced industrially as a racemate an equimolar mixture of two enantiomers by reduction of a ketone both enantiomers are able to lower blood pressure however recent research has shown that one enantiomer is preferred in medicines f i suggest a reducing agent that could reduce a ketone to form atenolol mark f ii draw a circle around the asymmetric carbon atom in the structure of atenolol shown below ch ch oh ch ch ch ch ch h n mark f iii suggest how you could show that the atenolol produced by reduction of a ketone was a racemate and not a single enantiomer marks f iv suggest one advantage and one disadvantage of using a racemate rather than a single enantiomer in medicines advantage disadvantage marks wmp jan chem turn over for the next question do not write on this page answer in the spaces provided turn over wmp jan chem
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Question 5 / 5

June 2013 QP – Unit 4 AQA Chemistry A-level_question_5 do not write outside the box lactic acid ch ch oh cooh is formed in the human body during metabolism and exercise this acid is also formed by the fermentation of carbohydrates such as sucrose c h o a i give the iupac name for lactic acid mark a ii write an equation for the formation of lactic acid from sucrose and water mark b a molecule of lactic acid contains an asymmetric carbon atom the lactic acid in the body occurs as a single enantiomer a racemic mixture racemate of lactic acid can be formed in the following two stage synthesis ch c o stage hcn ch c cn oh stage ch c cooh oh b i name and outline a mechanism for stage name of mechanism mechanism marks wmp jun chem do not write outside the box b ii give the meaning of the term racemic mixture racemate mark b iii explain how you could distinguish between a racemic mixture racemate of lactic acid and one of the enantiomers of lactic acid marks c a mixture of lactic acid and its salt sodium lactate is used as an acidity regulator in some foods an acidity regulator makes sure that there is little variation in the ph of food c i write an equation for the reaction of lactic acid with sodium hydroxide mark c ii the acid dissociation constant ka for lactic acid has the value mol dm at k calculate the ph of an equimolar solution of lactic acid and sodium lactate marks question continues on the next page turn over wmp jun chem do not write outside the box c iii suggest an alternative name for the term acidity regulator explain how a mixture of lactic acid and sodium lactate can act as a regulator when natural processes increase the acidity in some foods name explanation marks extra space d the cup shown is made from pla poly lactic acid pla is the condensation polymer formed from lactic acid the polymer is described as biodegradable and compostable compostable material breaks down slowly in contact with the moist air in a garden bin this produces compost that can be used to improve soil the manufacturers stress that pla cups differ from traditional plastic cups that are neither biodegradable nor compostable d i draw a section of pla that shows two repeating units marks wmp jun chem do not write outside the box d ii name the type of condensation polymer in pla mark d iii an intermediate in the production of pla is a cyclic compound c h o that is formed from two pla molecules draw the structure of this cyclic compound d iv traditional non biodegradable plastic cups can be made from poly phenylethene commonly known as polystyrene draw the repeating unit of poly phenylethene mark mark d v the manufacturers of pla claim that the material will break down to compost in just weeks suggest one reason why pla in landfill may take longer than weeks to break down mark turn over wmp jun chem
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