Edexcel Jun 2015 (IAL) Paper 2 Q23 (with explained solutions) |

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Edexcel Jun 2015 (IAL) Paper 2 Q23

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SECTION C Answer ALL the questions. Write your answers in the spaces provided. 23 Some organic molecules, either on their own or as part of a mixture, contribute to some very unpleasant odours. The molecule shown below, commonly called isovaleric acid, is responsible for the smell of sweaty feet. OH Isovaleric acid can be used to produce esters that have important industrial uses in the pharmaceutical industry, as sedatives and tranquilizers, and in the food industry, as flavouring and fragrance additives. The molecule with the systematic name (5(cid:302))-androst-16-en-3-one, labelled X in this question, is found in human sweat and urine. However, in other situations, these molecules can induce a very different effect. For example, X is present in commercial products used by pig farmers to determine when sows are ready for mating. (a) What is the systematic name for isovaleric acid? (1)(b) What is the molecular formula of isovaleric acid? (1)18 *P44882A01824*<br />
(c) Isovaleric acid has three structural isomers which are also carboxylic acids. One of these acids is drawn in the first box below. In the empty boxes below, draw the structures, using skeletal formulae, of the other two carboxylic acid structural isomers of isovaleric acid. OH valeric acid *(d) At room temperature, valeric acid is a liquid. It is sparingly soluble in water and very soluble in ethanol. Describe simple experiments you could carry out to show the different solubilities of valeric acid in these two solvents. No measurements are required, but you should state how you would make your experiments valid. State the expected observations from your experiments. (2) (3)*P44882A01924* 19 Turn over<br />
(e) Isoamyl alcohol is the alcohol from which isovaleric acid can be produced directly. This alcohol forms intermolecular hydrogen bonding. Using the simplified representation ROH, draw a hydrogen bond between two alcohol molecules and clearly indicate the bond angle about the hydrogen involved in the hydrogen bond. (f) There are also London forces between molecules of isoamyl alcohol. *(i) Describe how London forces are formed. (2) (2)(ii) The straight-chain structural isomer of isoamyl alcohol has a boiling temperature of 138C. Suggest whether the boiling temperature for isoamyl alcohol will be higher than, lower than or the same as the straight-chain isomer. Justify your choice. (3)20 *P44882A02024*<br />
(g) The molecule identified as X in the introduction to question 23, can be formed from the alcohol Y shown below. HO(cid:99) (i) The oxidation of an alcohol of this type with acidified sodium dichromate(VI) could involve either reflux or distillation. Explain why either could be used in this case. (1)(ii) An alternative reagent for the oxidation of an alcohol is acidified potassium manganate(VII), KMnO4. However, this is likely to produce other products because X contains another functional group that could react with this reagent. Name this other functional group in X and suggest the type of molecule formed in its reaction with acidified potassium manganate(VII), KMnO4. (2) Functional group that reactsType of molecule formed*P44882A02124* 21 Turn over<br />
*(h) Isovaleric acid and alcohol Y could react together to produce a compound with a pleasant aroma, but this can be masked by even a small residue of the starting molecules. Generally, spectroscopic methods are much more reliable than sense of smell in detecting the presence of molecules. The infrared absorption ranges associated with some functional groups are given below. OH stretching in alcohols OH stretching in carboxylic acids C=O stretching in aldehydes C=O stretching in ketones C=O stretching in carboxylic acids, alkyl CH stretching in alkane CH stretching in alkene 37503200 cm1 33002500 cm1 17401720 cm1 17001680 cm1 17251700 cm1 29622853 cm1 30953010 cm1 By quoting appropriate data, describe how both infrared spectroscopy and mass spectrometry could be used to determine the presence of isovaleric acid. The skeletal formula of isovaleric acid is shown below. OH (4)(Total for Question 23 = 21 marks) TOTAL FOR SECTION C = 21 MARKS TOTAL FOR PAPER = 80 MARKS 22 *P44882A02224*<br />

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Acceptable Answers Reject 2-methylbutanoic acid Mark 3(-)methylbutanoic acid ALLOW 3(-)methylbutyric acid Acceptable Answers C5H10O2 ALLOW atoms in any order if numbers are correct for each atom eg H10O2C5/ C5O2H10/ H10O2C5/ O2C5H10 ALLOW Additional formulae as well as correct answer Section C Question Number 23(a) Question Number 23(b) Question Number 23(c) Reject Just C4H9COOH Mark Acceptable Answers Reject O OH (1) O OH Mark Bonds may go in other directions eg methyl group upwards O OH (1)<br />
Acceptable Answers Question Number 23*(d) MP1 Reject Mark precipitate Equal/specified volumes/masses/amounts of solvent (1) MP2 Equal volumes of valeric acid and shake/stir/ mix (and allow to stand) OR Add valeric acid a drop at a time/from a burette to the solvents (1) MP3 (Two) layers with water and a (single) layer with ethanol OR Immiscible with water mixes with ethanol OR Cloudy with water and clear with ethanol OR Measure depth of mixture/smaller rise for ethanol (1)<br />
Reject Mark Question Number 23(e) Acceptable Answers Drawing of hydrogen bond between correct atoms and in a straight line Ignore extra molecules Ignore dipoles and omission of lone pair of electrons Ignore R-OH bond angle ALLOW Any alcohol (1) Bond angle 180 around the correct H atom and consequential on MP1 (1) NOTE If two water molecules/R-OH and a water molecule are correctly drawn with a linear hydrogen bond and 180 correctly labelled then award (1) Acceptable Answers Reject Mark Instantaneous dipole OR temporary asymmetric electron distribution (1) Induced dipole/charge in adjacent/another molecule/atom/particle (1) Question Number 23(f)*(i)<br />
Acceptable Answers (Boiling temperature will be) lower/ straight chain is higher (1) Remaining marks are dependent on MP1 MP2 and MP3 Branching reduces/ less(ens)/weakens the London/dispersion/ Van der Waals/vdW forces (1) (because it has) less surface area (in contact)/ molecules cant align/molecules cant get as close (1) OR Straight chain stronger/ more/ increases London/etc forces (1) (because it has) greater surface area (in contact) /molecules can align better/molecules can get as closer/pack more closely (1) IGNORE References to energy Reject Mark Acceptable Answers (The alcohol) can only be oxidized to the ketone OR cannot be further oxidized OR cannot be oxidized to a carboxylic acid OR Further oxidation would have to break a C-C bond IGNORE Its a secondary alcohol/Its not a primary alcohol/ Same product formed Question Number 23(f)(ii) MP1 Reject Mark Question Number 23(g)(i)<br />
Mark Reject Just double bond Alcohol Acceptable Answers Question Number 23(g)(ii) Alkene/carbon-carbon double bond ALLOW C=C (1) (Type of molecule) (1,2-) diol ALLOW (1,2-) dialcohol (1)<br />
3095-3010 3750-3200 1700-1680 Up to 2 marks for IR points Penalise the omission of bonds once only IR MP1 3300-2500 (cm-1) OH/OH (stretch in a carboxylic acid) (1) IR MP2 1725-1700 (cm-1) C=O (stretch in a carboxylic acid) (1) Ignore 29622853 (cm-1) C-H (stretch in an alkane) Up to 3 marks for Mass Spec points Only penalise negative charges or lack of positive charge once Molecular ion/parent ion peak /C5H10O2 C5H9O2 COOH+ at 45 (1) C4H9 C4H7O2 OH+ at 17 (1) CH3 + at 15 (1) +/CH3CHCH2CO2H+ at 87 (1) +/CH3CH(CH3)CH2 + at 57 (1) + at 101 (1) + at 102 (1) Acceptable Answers Reject Mark Question Number 23(h) TOTAL FOR SECTION C (QUESTION 23) = 21 MARKS TOTAL FOR PAPER = 80 MARKS<br />

Question 18 19 20 21 22 23

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