1 Chromatography

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Oxford Textbook Pages : 496 - 499

CGP Revision Guide Pages : 198 - 201

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Show Specification Ref : 3.3.16

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Question 1 / 4

January 2011 QP – Unit 4 AQA Chemistry A-level_question_4 do not write outside the box a name compound y hoch ch cooh mark b under suitable conditions molecules of y can react with each other to form a polymer b i draw a section of the polymer showing two repeating units mark b ii name the type of polymerisation involved mark c c i when y is heated an elimination reaction occurs in which one molecule of y loses one molecule of water the organic product formed by this reaction has an absorption at cm in its infrared spectrum identify the bond that causes the absorption at cm in its infrared spectrum mark c ii write the displayed formula for the organic product of this elimination reaction c iii the organic product from part c ii can also be polymerised draw the repeating unit of the polymer formed from this organic product mark mark wmp jan chem do not write outside the box d at room temperature aminobutanoic acid exists as a solid draw the structure of the species present in the solid form e the amino acid glutamic acid is shown below mark draw the structure of the organic species formed when glutamic acid reacts with each of the following e i an excess of sodium hydroxide e ii an excess of methanol in the presence of concentrated sulfuric acid e iii ethanoyl chloride question continues on the next page mark mark mark turn over wmp jan chem do not write outside the box f a tripeptide was heated with hydrochloric acid and a mixture of amino acids was formed this mixture was separated by column chromatography outline briefly why chromatography is able to separate a mixture of compounds practical details are not required 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 2 / 4

June 2010 QP – Unit 4 AQA Chemistry A-level_question_4 do not write outside the box in some food products containing pork were withdrawn from sale because tests showed that they contained amounts of compounds called dioxins many times greater than the recommended safe levels dioxins can be formed during the combustion of chlorine containing compounds in waste incinerators dioxins are very unreactive compounds and can therefore remain in the environment and enter the food chain many dioxins are polychlorinated compounds such as tetrachlorodibenzodioxin tcdd shown below cl cl cl cl in a study of the properties of dioxins tcdd and other similar compounds were synthesised the mixture of chlorinated compounds was then separated before each compound was identified by mass spectrometry a fractional distillation is not a suitable method to separate the mixture of chlorinated compounds before identification by mass spectrometry suggest how the mixture could be separated mark b the molecular formula of tcdd is c h o cl chlorine exists as two isotopes cl and cl deduce the number of molecular ion peaks in the mass spectrum of tcdd and calculate the m z value of the most abundant molecular ion peak number of molecular ion peaks m z value of the most abundant molecular ion peak marks c suggest one operating condition in an incinerator that would minimise the formation of dioxins mark wmp jun chem do not write outside the box d tcdd can also be analysed using c n m r d i give the formula of the compound used as the standard when recording a c spectrum mark d ii deduce the number of peaks in the c n m r spectrum of tcdd mark turn over for the next question turn over wmp jun chem
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Question 3 / 4

June 2012 QP – Unit 4 AQA Chemistry A-level_question_7 do not write outside the box a a chemist discovered four unlabelled bottles of liquid each of which contained a different pure organic compound the compounds were known to be propan ol propanal propanoic acid and chloropropane describe four different test tube reactions one for each compound that could be used to identify the four organic compounds your answer should include the name of the organic compound the reagent s used and the expected observation for each test marks extra space wmp jun chem do not write outside the box b a fifth bottle was discovered labelled propan ol the chemist showed using infrared spectroscopy that the propan ol was contaminated with propanone the chemist separated the two compounds using column chromatography the column contained silica gel a polar stationary phase the contaminated propan ol was dissolved in hexane and poured into the column pure hexane was added slowly to the top of the column samples of the eluent the solution leaving the bottom of the column were collected suggest the chemical process that would cause a sample of propan ol to become contaminated with propanone state how the infrared spectrum showed the presence of propanone suggest why propanone was present in samples of the eluent collected first those with shorter retention times whereas samples containing propan ol were collected later marks extra space turn over for the next question turn over wmp jun chem
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Question 4 / 4

June 2014 QP – Unit 4 AQA Chemistry A-level_question_6 do not write outside the box lysine and alanine are two amino acids ch h n ch c cooh h c cooh nh lysine nh alanine a give the iupac name of lysine mark b b i draw structures to show the product formed in each case when lysine reacts with an excess of aqueous hcl b ii an excess of aqueous naoh b iii methanol in the presence of a small amount of concentrated h so mark mark mark wmp jun chem do not write outside the box c the mass spectrum of alanine gives a major peak at m z write an equation for the fragmentation of the molecular ion of alanine to give an ion that produces this peak in your answer draw the displayed formula for this fragment ion marks d draw a dipeptide formed from one molecule of lysine and one molecule of alanine mark e the dipeptide in question d is hydrolysed in acid conditions and the mixture produced is analysed by column chromatography the column is packed with a resin which acts as a polar stationary phase suggest why lysine leaves the column after alanine marks turn over wmp jun chem
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