OCR A LEVEL CHEMISTRY aromatic compounds ALL QUESTIONS

1 This question is about the chemistry of compounds containing phosphorus.


When phosphorus(V) chloride, PCl5, and ammonium chloride are heated together, the compound P3N3Cl6 is
formed, together with HCl gas.


P3N3Cl6 has a cyclic structure, like the Kekulé structure of benzene.



i. Write an equation for the reaction of PCl5 and ammonium chloride to form P3N3Cl6.


[1]

ii. Calculate the percentage by mass of P in P3N3Cl6.


Give your answer to 2 decimal places.




percentage by mass of P = ................... % [2]


iii. Suggest one example of evidence that could show that P3N3Cl6 has a Kekulé structure rather than a
delocalised structure.




[1]

iv. In a molecule of P3N3Cl6 all the N and Cl atoms are bonded to P atoms.
Suggest a possible structure for a molecule of P3N3Cl6.




[2]




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, 2 This question is about the analysis of organic compounds.


Compounds F, G, H and I are structural isomers.


A student carries out test-tube tests on the compounds.
The student records the observations after carrying out each test.
These are shown in Table 5.1.


In Table 5.1, 2,4-dintrophenylhydrazine has been abbreviated to 2,4–DNP.


Table 5.1



Compound Test
2,4-DNP Acidified Bromine water Tollens' reagent
dichromate(VI)
reflux
F Orange solution Green solution Colourless solution Colourless solution
G Orange solution Green solution Orange solution Colourless solution
H Orange precipitate Orange solution Orange solution Colourless solution
I Orange precipitate Green solution Orange solution Silver mirror



i. Write the formula of the species causing the colours after refluxing with acidified dichromate(VI).


Green solution


Orange solution [2]




ii. The student is provided with further information about compounds F–I.


• They all have the molecular formula C5H10O.
• One of the compounds is alicyclic.
• The other compounds are unbranched.


Use this further information and the student’s observations in Table 5.1 to answer the following.


• How do the observations provide evidence for the possible functional groups in compounds F–I?
• Suggest a possible structure for each of the compounds F–I.
Show your reasoning.




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, Extra answer space if required.




[6]




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, 3 Oil of wintergreen is a liquid used in medicine to relieve muscle pain.


Compound H is a component in oil of wintergreen and can be synthesised from compound G, as shown below.
The boiling point and density of compound H are stated.




A student prepares a sample of compound H by the method below.


Step 1 Reflux 8.97 g of compound G for 30 minutes with an excess of methanol in the presence of a small
amount of sulfuric acid as a catalyst.
Step 2 Add an excess of aqueous sodium carbonate, Na2CO3(aq). Two layers are obtained.
Step 3 Purify the impure compound H that forms from the resulting mixture.


The student follows this method and obtains 5.32 g of pure compound H.




i. In Step 2, Na2CO3(aq) removes the sulfuric acid catalyst and any unreacted compound G from the mixture.


Write equations for this removal.


Removal of sulfuric acid




Removal of unreacted compound G




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