A Level Official Exam Material
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Unit 1: Structure, Bonding and Introduction to Organic Chemistry
Topic 4: Introductory Organic Chemistry and Alkanes
For both AS and A Level students
Q1. An electrophile
A accepts a pair of electrons
B always has a negative charge
C always has a positive charge
D donates a pair of electrons
(Total for question = 1 mark)
Q2. What is the total number of structural isomers with the molecular formula C6H14?
A 4
B 5
C 6
D 7
(Total for question = 1 mark)
Q3. Members of the homologous series of alkanes have the same
A boiling temperature
B density
C empirical formula
D general formula
(Total for question = 1 mark)
Q4. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
A substance is labelled with the hazard symbol shown.
What is the meaning of this symbol?
A gloves must be worn
B corrosive
C do not store with flammable substances
D oxidising
(Total for question = 1 mark)
Q5. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
When C20H42 is cracked, each molecule produces one molecule of ethene, one molecule of butane and two molecules of hydrocarbon E.
What is the molecular formula of E?
A C7H13
B C7H14
C C14H26
D C14H28
Use this space for any rough working.
Anything you write in this space will gain no credit.
(Total for question = 1 mark)
Q6. During a cracking reaction, each molecule of an alkane with formula C10H22 formed only two molecules of ethene and one molecule of hydrocarbon A.
What is the molecular formula of A? (1)
A C6H10
B C6H14
C C8H16
D C8H18
(Total for question = 1 mark)
Q7. The alkanes are a homologous series of saturated hydrocarbons.
(a) Draw the displayed formulae of the three alkanes with molecular formula C5H12. (3)
(b) Give the systematic name of compound P. (1)
Systematic name .............................................................................................................................................
(c) The table shows the boiling temperatures of the first four straight-chain alkanes.
Predict the molecular formula and boiling temperature of the straight-chain alkane that has five carbon atoms in its molecules. (2)
Molecular formula .........................................................................
Boiling temperature ....................................................................
(d) Alkanes undergo incomplete combustion when they burn in a limited supply of air.
(i) Write the equation for the incomplete combustion of propane, C3H8, to form carbon, carbon monoxide, carbon dioxide and water. State symbols are not required. (1)
(ii) Explain the toxicity of carbon monoxide. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. (e)
Propane reacts with chlorine in the presence of ultraviolet radiation.
The reaction starts when some chlorine molecules are split into free radicals.
A mixture of products is formed.
(i) Write the two propagating steps to show how C3H7Cl is formed.
Curly arrows are not required. (2)
(ii) Identify the different C3H7Cl molecules that are produced in this reaction. (1) ............................................................................................................................................. .............................................................................................................................................
(iii) Give a reason why a mixture of C3H7Cl molecules is formed. (1) ............................................................................................................................................. .............................................................................................................................................
(iv) Give a reason why some hexane is formed in this reaction. (1) ............................................................................................................................................. .............................................................................................................................................
(v) A small amount of a product with molar mass 113 g mol−1 is formed.
Deduce the structure and name of a possible product with this molar mass. (2)
Structure .............................................................................................................................................
Name .............................................................................................................................................
(Total for question = 16 marks)
Q8. Heptane, C7H16, is one of the compounds present in crude oil.
(a) When heptane is reformed, the products include 2,2,3-trimethylbutane and cycloheptane.
(i) Give a reason why petrol should not contain a high proportion of heptane. (1) ............................................................................................................................................. .............................................................................................................................................
(ii) Draw the skeletal formula of 2,2,3-trimethylbutane. (1)
(iii) Write the equation for reforming heptane into cycloheptane.
Use molecular formulae. State symbols are not required. (1)
(iv) When petrol is burned in a car engine, oxides of nitrogen are formed.
Explain how these compounds result in damage to trees. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(b) Heptane reacts with chlorine in sunlight.
(i) Chlorine radicals are formed in the first step in the mechanism. Cl2 → 2Cl• Name this step in the mechanism. (1) .............................................................................................................................................
(ii) Give the two propagation steps for the formation of chloroheptane.
Use molecular formulae. Curly arrows are not required. (2)
(iii) Give the termination step which forms a hydrocarbon. (1)
(iv) Explain how some dichloroheptane, C7H14Cl2 , also forms during this reaction.
You may include equation(s) in your answer. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(Total for question = 11 marks)
Q9. Heptane, C7H16, is an alkane found in crude oil.
(a) Heptane can undergo incomplete combustion.
(i) Give a reason why incomplete combustion sometimes occurs. (1) ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(ii) Write the equation for the incomplete combustion of heptane, forming carbon monoxide and water as the only products. State symbols are not required. (1)
(b) Heptane is reformed into branched-chain and cyclic hydrocarbons that are used in petrol.
(i) Draw the skeletal formulae of a branched-chain alkane and a cycloalkane, each containing seven carbon atoms. (2)
(ii) Write the equation for the reforming of heptane into a cycloalkane.
Use molecular formulae. (1) (iii) Give a reason for adding cycloalkanes to petrol. (1)
............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(c) Heptane, C7H16 , reacts with chlorine in the presence of ultraviolet radiation.
(i) State the type and mechanism of this reaction. (2)
.............................................................................................................................................
(ii) Give the mechanism for the reaction to produce C7H15Cl, C14H30 and HCl as the only products.
Include the name of each of the steps in your mechanism.
Curly half-arrows are not required. (7)
(Total for question = 15 marks)
Q10. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
Petrol, bioethanol and hydrogen are fuels.
All three of these fuels
A burn to produce greenhouse gases
B are overall carbon neutral
C are overall sustainable D biodegrade rapidly
(Total for question = 1 mark)
Q11. Which of these fuels is obtained from fermented sugar cane? (1)
A ethanol
B hydrogen
C petrol
D propane
(Total for question = 1 mark)
Q12. Curly arrows are used in reaction mechanisms
The curly arrow shown represents the movement of (1)
A an electron from a bond to an atom, forming free radicals
B an electron from a bond to an atom, forming ions
C a pair of electrons from a bond to an atom, forming free radicals
D a pair of electrons from a bond to an atom, forming ions
(Total for question = 1 mark)
Q13. This question is about cycloalkanes. (a)
When alkanes from crude oil are reformed, the products include cycloalkanes.
Write the equation for reforming hexane into cyclohexane using skeletal formulae for the organic compounds. (2)
Q14. This question is about fuels and polymers.
Used coffee grounds have been suggested as a carbon-neutral fuel to replace some fossil fuels. (a)
(i) Explain why coffee grounds might be considered a carbon-neutral fuel. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(ii) Explain how the use of fossil fuels causes climate change. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(b) Long chain alkanes are not normally used as fuels as they produce soot.
(i) Name another pollutant formed by incomplete combustion of alkanes. (1) .............................................................................................................................................
(ii) Write the equation for the complete combustion of octane.
State symbols are not required. (2)
(c) Long chain alkanes are converted into smaller, more useful molecules including alkenes.
(i) Name this process. (1)
.............................................................................................................................................
(Total for question = 8 marks)
Q15. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
What is the empirical formula of butane?
A C4H10
B C2H5
C CH2.5
D CnH2n + 2
(Total for question = 1 mark)
Q16. Which of these is not a chemical reaction? (1)
A cracking
B fractional distillation
C polymerisation
D reforming
(Total for question = 1 mark)
Q17. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross . Cyclopentane undergoes free radical substitution with bromine.
(a) Which of these is an overall equation for this reaction? (1)
A C5H8 + Br2 → C5H8Br2
B C5H10 + Br2 → C5H10Br2
C C5H10 + Br2 → C5H8Br2 + H2
D C5H10 + Br2 → C5H9Br + HBr
(b) Which statement is not correct about this reaction system? (1)
A only the initiation step involves homolytic bond fission
B only some bromine is converted to free radicals in the initiation step
C propagation forms more product than termination
D further substitution reactions are likely to occur
Q9. In the reaction of methane with chlorine, ultraviolet light causes
A homolytic fission of the Cl—Cl bond in chlorine molecules.
B heterolytic fission of the Cl—Cl bond in chlorine molecules.
C homolytic fission of the C—H bond in methane molecules.
D heterolytic fission of the C—H bond in methane molecules.
(Total for question = 1 mark)
Q10. The ionic equation for the reaction between hydrochloric acid and aqueous sodium hydroxide is
A H+ (aq) + OH− (aq) → H2O(l)
B Cl− (aq) + Na+ (aq) → NaCl(aq)
C H+ (aq) + Cl− (aq) + Na+ (aq) + OH− (aq) → Cl− (aq) + Na+ (aq) + H2O(l)
D H+ (aq) + Cl− (aq) + Na+ (aq) + OH− (aq) → NaCl(aq) + H2O(l)
(Total for question = 1 mark)
Q11. In the United Kingdom, the limit for gaseous hydrocarbons in vehicle exhaust gases is 200 ppm.
What is the maximum volume of gaseous hydrocarbons allowed in 10 mol of exhaust gases, at room temperature and pressure?
[Molar volume = 24 dm3 mol–1 ]
A 24 cm3
B 48 cm3
C 96 cm3
D 480 cm3
(Total for question = 1 mark)
Q12. How many straight chain isomers have the molecular formula C3H5Cl?
A 3
B 4
C 5
D 6
(Total for question = 1 mark)
Q13. This question is about alkanes and their use as fuels.
Crude oil is a mixture of alkanes which can be processed in various ways.
(a) Fractional distillation is the method used to separate crude oil into fractions containing similar sized alkanes
(i) On what physical property does the separation of alkanes using fractional distillation depend? (1) ............................................................................................................................................. .............................................................................................................................................
(ii) Suggest the name of an alkane that would be present in the fraction labelled A. (1) .............................................................................................................................................
(iii) State why fractions in addition to B are also processed to produce petrol. (1) ............................................................................................................................................. .............................................................................................................................................
(b) Substances obtained from crude oil can be processed by cracking to obtain alkanes and alkenes.
(i) Industrial catalysts are used for the cracking process.
What other condition is required? (1) .............................................................................................................................................
(ii) The kerosene fraction contains the hydrocarbon, C12H26, which can be cracked to produce octane and ethene only. Write the equation for this cracking reaction.
State symbols are not required. (2)
(c) Substances obtained from crude oil can be processed by reforming to produce branched-chain alkanes from straight-chain alkanes.
(i) State the advantage of using petrol containing branched-chain alkanes. (1) ............................................................................................................................................. .............................................................................................................................................
(ii) Using skeletal formulae, write an equation for the reforming of hexane into an alkane with a single branch as the only product.
Name your product.
State symbols are not required. (3)
Q14. Crude oil is a source of alkanes.
(a) Name the process by which the hydrocarbons in crude oil are separated. (1) .............................................................................................................................................
(b) The alkane X is composed of straight-chain molecules, each with nine carbon atoms.
(i) Give the molecular formula of X. (1) .............................................................................................................................................
(ii) Y is a branched-chain isomer of X. Y has eight carbon atoms in a straight-chain with one methyl group as a side-chain. Draw the skeletal formula of one possible structure for Y.
Give the name of the structure that you have drawn. (2)
Skeletal formula:
Name: .............................................................................................................................................
(c) A reaction called cracking occurs when the alkane pentadecane, C15H32, is heated in the presence of a catalyst.
(i) Give an equation to show the cracking of one molecule of C15H32 to form one molecule of ethene and a molecule of one other product.
State symbols are not required. (1)
(ii) In practice, cracking pentadecane forms a large number of products.
Suggest why this is so. (1)
............................................................................................................................................. .............................................................................................................................................
Q15. 100 cm3 of methane, CH4, is completely burned in 400 cm3 of oxygen.
What is the final volume of the gas mixture, in cm3 , when all volumes are measured at room temperature and pressure?
A 100
B 200
C 300
D 400
(Total for question = 1 mark)
Q16. When ethane reacts with chlorine, a mixture of products forms.
Which product is the best evidence for a free radical mechanism?
A HCl
B C4H10
C C2H5Cl
D C2H4Cl2
(Total for question = 1 mark)
If you need the markscheme, including the examiners' reports for each question, and more exam and teaching materials on this topic, contact me through the contact page