Organic Chemistry: Halogenoalkanes, Alcohols and SpectraEdexcel International A Level Chemistry: Topic test

1. 1
   Chloroethane is converted into ethylamine by heating it with ammonia dissolved in ethanol in a sealed tube under pressure: CH₃CH₂Cl + 2NH₃ → CH₃CH₂NH₂ + NH₄Cl.

   (a)

   What is the role of ammonia in the first step of this reaction?

   [1 mark]

   • AA nucleophile, because it donates a lone pair of electrons to a carbon atom
   • BAn electrophile, because it accepts a pair of electrons from carbon
   • CA free radical, because it forms a bond using one unpaired electron
   • DAn oxidising agent, because it removes electrons from chlorine

   (b)

   Why is the carbon atom of the C–Cl bond attacked by ammonia?

   [1 mark]

   • AChlorine is less electronegative than carbon, so the carbon atom carries a partial negative charge
   • BThe C–Cl bond is non-polar, so it is attacked by free radicals
   • CChlorine is more electronegative than carbon, so the carbon atom carries a partial positive charge
   • DThe hydrogen atoms on the carbon withdraw electrons from the C–Cl bond

   (c)

   Describe the first step of the mechanism of this reaction, in terms of the movement of electron pairs, and name the type of mechanism.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemist studies the halogenoalkane 1-iodo-2-methylpropane, (CH₃)₂CHCH₂I.

   (a)

   How is this halogenoalkane classified?

   [1 mark]

   • ASecondary, because the carbon chain contains a branch
   • BPrimary, because the carbon atom bonded to iodine is attached to only one other carbon atom
   • CTertiary, because it contains a CH(CH₃)₂ group
   • DIt cannot be classified because the molecule is branched

   (b)

   The halogenoalkane is heated with ethanolic potassium hydroxide. What is the organic product?

   [1 mark]

   • A2-methylpropan-1-ol, formed by substitution
   • BBut-1-ene, formed by elimination
   • C2-methylpropanenitrile, formed by substitution
   • D2-methylpropene, formed by elimination

   (c)

   Explain how the role of the hydroxide ion differs when 1-iodo-2-methylpropane reacts with aqueous potassium hydroxide and with ethanolic potassium hydroxide.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The rates of hydrolysis of the 1-halopropanes, CH₃CH₂CH₂X, are compared by warming each with aqueous sodium hydroxide, then acidifying with dilute nitric acid and adding aqueous silver nitrate to test for halide ions. Mean bond enthalpies in kJ mol⁻¹: C–F 467, C–Cl 346, C–Br 290, C–I 228. Relative atomic mass: Ag = 107.9, Br = 79.9.

   (a)

   Explain the trend in the rate of hydrolysis of the four 1-halopropanes in terms of bond enthalpy.

   [3 marks]

   (b)

   In one test 0.0040 mol of 1-bromopropane is fully hydrolysed. Write the ionic equation for the reaction of the halide ion in the silver nitrate test, calculate the mass of precipitate formed, and state the colours of the precipitates from 1-bromopropane and 1-iodopropane.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student has two unlabelled colourless liquids, pentan-2-ol and 2-methylbutan-2-ol, both with molecular formula C₅H₁₂O. She identifies them with chemical tests and then confirms the organic product of one test by spectroscopy. Infrared data: O–H (alcohols) 3230–3550 cm⁻¹; C=O 1680–1750 cm⁻¹; C–H 2850–3100 cm⁻¹. Relative atomic masses: H = 1.0, C = 12.0, O = 16.0.

   (a)

   Describe how acidified potassium dichromate(VI) can be used to distinguish the two alcohols. Give the observations, name the organic product formed with one of them, and write an equation for its formation using [O] to represent the oxidising agent.

   [6 marks]

   (b)

   Explain how infrared and mass spectra would show that pentan-2-ol had been converted into pentan-2-one, CH₃COCH₂CH₂CH₃. Include the molecular ion peak of each compound and the m/z values of two fragment ions from pentan-2-one, with their formulae.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A chemist investigates reactions of propan-1-ol, CH₃CH₂CH₂OH, which can be converted into a chloroalkane by phosphorus(V) chloride, and into an alkene by heating with concentrated phosphoric acid.

   (a)

   What is observed when solid phosphorus(V) chloride is added to dry propan-1-ol?

   [1 mark]

   • AThe solution turns from orange to green
   • BBrown fumes of bromine
   • CA white precipitate of silver chloride
   • DSteamy white fumes of hydrogen chloride

   (b)

   Which equation represents the reaction of propan-1-ol with phosphorus(V) chloride?

   [1 mark]

   • ACH₃CH₂CH₂OH + PCl₅ → CH₃CH₂CH₂Cl + POCl₃ + HCl
   • BCH₃CH₂CH₂OH + PCl₅ → CH₃CH=CH₂ + POCl₃ + 2HCl
   • CCH₃CH₂CH₂OH + PCl₅ → CH₃CH₂CH₂Cl + PCl₃ + H₂O
   • DCH₃CH₂CH₂OH + 2PCl₅ → CH₃CH₂CH₂Cl + POCl₃ + HCl

   (c)

   Propan-1-ol is heated with concentrated phosphoric acid to form propene. Write an equation for the reaction and name the type of reaction.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A compound R has molecular formula C₄H₈O. Its mass spectrum has a molecular ion peak at m/z 72 and fragment peaks at m/z 57, 43 and 29. Its infrared spectrum has a strong, sharp absorption at 1715 cm⁻¹ and no broad absorption between 2500 and 3550 cm⁻¹.

   (a)

   What does the infrared spectrum of R show?

   [1 mark]

   • AAn O–H bond in a carboxylic acid is present
   • BA C=C bond is present
   • CA C=O bond is present and there is no O–H bond
   • DAn N–H bond is present

   (b)

   The peak at m/z 57 is formed from the molecular ion. Which fragment has been lost?

   [1 mark]

   • AA CH₂ group, of relative mass 14
   • BA CH₃ group, of relative mass 15
   • CAn OH group, of relative mass 17
   • DAn oxygen atom, of relative mass 16

   (c)

   Explain how the molecular ion is formed in a mass spectrometer and why the fragment peaks seen in the spectrum arise from ions rather than from all of the pieces formed when the molecular ion breaks up.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A student oxidises 8.80 g of pentan-1-ol (Mr = 88.0) by adding it dropwise to warm acidified potassium dichromate(VI) and distilling off the product as it forms. The product is pentanal (Mr = 86.0). Boiling temperatures: pentan-1-ol 138 °C, pentanal 103 °C, pentanoic acid 186 °C.

   (a)

   Explain why the student distils the pentanal as it forms, rather than heating the mixture under reflux.

   [3 marks]

   (b)

   The student collects 5.16 g of pure pentanal. Calculate the percentage yield and suggest one reason why it is less than 100%.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A chemist converts propan-1-ol into three different organic products. Product X is formed by heating it under reflux with excess acidified potassium dichromate(VI). Product Y is formed by heating it with concentrated phosphoric acid. Product Z is formed by warming it with potassium bromide and 50% concentrated sulfuric acid. Infrared data: C=C 1620–1669 cm⁻¹; C=O 1680–1750 cm⁻¹; O–H (carboxylic acids) 2500–3300 cm⁻¹. Relative atomic masses: H = 1.0, C = 12.0, O = 16.0.

   (a)

   Identify X, Y and Z. For each, write an equation (using [O] for the oxidising agent where needed) and name the type of reaction.

   [6 marks]

   (b)

   Explain how infrared spectroscopy, the molecular ion peaks in the mass spectra and a simple chemical test could each be used to distinguish X from Y.

   [6 marks]

   Total for question 8: 12 marks

End of questions