Introductory Organic Chemistry and AlkanesEdexcel International A Level Chemistry: Topic test

1. 1
   A technician cleans laboratory glassware with propanone, CH₃COCH₃. Propanone is highly flammable and its vapour irritates the eyes. Large bottles of it are kept in the preparation room.

   (a)

   Which statement correctly distinguishes a hazard from a risk?

   [1 mark]

   • AA hazard is the likelihood that harm will occur; a risk is the potential of a substance to cause harm
   • BA hazard is the potential of a substance to cause harm; a risk is the likelihood that the harm will occur
   • CA hazard applies only to organic compounds; a risk applies only to inorganic compounds
   • DA hazard can be reduced by good practice; a risk is fixed for a substance

   (b)

   Which change reduces the risk from using propanone without changing its hazard?

   [1 mark]

   • AReplacing it with a more flammable solvent
   • BWarming it to make it evaporate faster
   • CPouring it from a larger container
   • DUsing a smaller volume in a fume cupboard, away from naked flames

   (c)

   Suggest two ways in which the risk from the propanone could be reduced, and explain why a risk assessment is carried out before it is used.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student studies three changes. Reaction 1: but-2-ene reacts with hydrogen in the presence of a nickel catalyst to form butane. Reaction 2: many molecules of chloroethene join together to form poly(chloroethene), PVC. Reaction 3: a chlorine molecule absorbs ultraviolet light and splits into two chlorine atoms.

   (a)

   Which type of reaction is Reaction 2?

   [1 mark]

   • APolymerisation
   • BSubstitution
   • COxidation
   • DReduction

   (b)

   Which statement describes the bond fission in Reaction 3?

   [1 mark]

   • AHeterolytic fission, producing a Cl⁺ ion and a Cl⁻ ion
   • BHeterolytic fission, producing two free radicals
   • CHomolytic fission, producing two free radicals
   • DHomolytic fission, producing two ions

   (c)

   Define the term free radical and the term electrophile.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Liquefied petroleum gas (LPG) used for heating contains butane, C₄H₁₀, and its branched isomer. Cycloalkanes with the molecular formula C₄H₈ also exist.

   (a)

   State the general formula of the alkanes, explain what is meant by saturated, and explain what is meant by structural isomers.

   [3 marks]

   (b)

   Give the name and the structural formula of the branched isomer of butane. Name the two cycloalkanes with the molecular formula C₄H₈, and explain why their molecular formula does not fit the general formula of the alkanes.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Crude oil contains many long-chain alkanes for which there is little demand as fuels. Refineries convert them into shorter molecules and into branched or cyclic molecules. Hexane, C₆H₁₄, can be converted into cyclohexane, C₆H₁₂, which can then be used as a starting material for other reactions.

   (a)

   Describe what happens in cracking and in reforming, give a balanced equation for each, using the cracking of dodecane, C₁₂H₂₆, to an alkane and ethene, and the reforming of hexane to cyclohexane, and explain why each process is carried out.

   [6 marks]

   (b)

   Cyclohexane reacts with bromine in ultraviolet light to form bromocyclohexane, C₆H₁₁Br, and hydrogen bromide. Describe the mechanism of this reaction, naming it and giving the equations for each step, and explain why the reaction is of limited use for making bromocyclohexane.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   Compound Z has the structural formula CH₃CH(CH₃)CH₂CH(CH₃)CH₃.

   (a)

   What is the IUPAC name of compound Z?

   [1 mark]

   • A3,5-dimethylpentane
   • B2,4-dimethylhexane
   • C2,4-dimethylpentane
   • Dheptane

   (b)

   Which compound is a structural isomer of compound Z?

   [1 mark]

   • A3-ethylpentane
   • B2,4-dimethylhexane
   • Ccycloheptane
   • D2,3-dimethylbutane

   (c)

   Explain what is meant by a homologous series, and state one way in which the members of the alkane homologous series are similar or change gradually.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   Container ships burn heavy fuel oil, which contains sulfur compounds as impurities. The exhaust gases contain carbon dioxide, sulfur dioxide, oxides of nitrogen, carbon monoxide and carbon particulates.

   (a)

   Which pollutant is formed from the sulfur impurities in the fuel and is acidic?

   [1 mark]

   • ACarbon monoxide
   • BCarbon particulates
   • COxides of nitrogen
   • DSulfur dioxide

   (b)

   How do oxides of nitrogen form in the ship's engine?

   [1 mark]

   • AAlkanes in the fuel react with nitrogen at room temperature
   • BNitrogen and oxygen from the air react at the high temperatures in the engine
   • CIncomplete combustion of the carbon in the fuel
   • DSulfur dioxide reacts with the alkanes in the fuel

   (c)

   The company considers using hydrogen as a fuel. Explain why hydrogen is described as carbon neutral when it is burned, but may not be carbon neutral overall.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A camping lighter contains butane, C₄H₁₀ (molar mass 58.0 g mol⁻¹). Relative atomic masses: C = 12.0, H = 1.0, O = 16.0.

   (a)

   Write a balanced equation for the complete combustion of butane. State the conditions under which carbon monoxide forms instead, and write a balanced equation for the formation of carbon monoxide and water from butane.

   [3 marks]

   (b)

   A lighter burns 2.90 g of butane completely. Calculate the mass of carbon dioxide formed.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A student plans to crack liquid paraffin, a mixture of long-chain alkanes. The vapour is passed over hot aluminium oxide pellets in a heated tube, and the gas produced is collected over water in an inverted test tube.

   (a)

   Using this practical as an example, distinguish between a hazard and a risk, suggest three ways of reducing the risk, and explain why a risk assessment is needed.

   [6 marks]

   (b)

   The gas collected decolourises bromine water and burns with a sooty flame. Name the type of reaction with bromine water and explain what the first observation shows. Explain why carbon particulates and carbon monoxide are formed when a hydrocarbon burns with limited oxygen, and why carbon monoxide is toxic.

   [6 marks]

   Total for question 8: 12 marks

End of questions