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ASChemistryEdexcelExam Questions3. Organic Chemistry3.2 Alkanes

Alkanes (Edexcel AS Chemistry)

Exam Questions

28 mins4 questions
Easy
Medium
1a4 marks

Some alkanes are used as fuels for transport. Crude oil, which is a mixture of hydrocarbons, is the major source of these alkanes. Crude oil is processed by fractional distillation, cracking and reforming.

Fractional distillation produces fractions which contain molecules of a similar boiling temperature. Molecules containing six carbon atoms are found in both the petrol fraction and the higher boiling kerosene fraction.

i)
Identify, by name or structural formula, the unbranched alkane with six carbon atoms found in kerosene.

(1)

ii)
Explain why isomers of the alkane in (a)(i) have lower boiling temperatures and so are found in the petrol fraction.

(3)

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1b3 marks

During cracking, carbon to carbon bonds are broken.

Explain the two major reasons for cracking hydrocarbons.

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1c1 mark

Which of the following changes to the proportions of organic molecules within a fraction results from the reforming process?

      Proportion of branched chain alkanes Proportion of cyclic hydrocarbons
  ☐ A decrease decrease
  ☐ B decrease increase
  ☐ C increase decrease
  ☐ D increase increase

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2a1 mark

This question is about alkanes.

The reaction of ethane and chlorine in UV radiation produces chloroethane.

C2H6 + Cl2 → C2H5Cl + HCl

This reaction is classified as

  ☐ A addition
  ☐ B elimination
  ☐ C initiation
  ☐ D substitution

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2b1 mark

The black smoke produced from the incomplete combustion of alkane fuels is

  ☐ A carbon particulates
  ☐ B oxides of nitrogen
  ☐ C oxides of sulfur
  ☐ D unburnt hydrocarbons

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2c1 mark

A reaction of hexane is shown below.

q1c-9cho-al-2-june-2018-qp-edexcel-a-level-chem

This is best described as

  ☐ A elimination
  ☐ B hydrogenation
  ☐ C isomerisation
  ☐ D reforming

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2d1 mark

The skeletal formula of decalin is

q1d-9cho-al-2-june-2018-qp-edexcel-a-level-chem

The molecular formula of decalin is

  ☐ A C10H22
  ☐ B C10H20
  ☐ C C10H18
  ☐ D C10H16

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3a2 marks

This question concerns the combustion of fossil fuels in power stations.

One type of power station uses the combustion of methane gas to generate power.

Write an equation for the incomplete combustion of methane gas to form carbon monoxide and water only. State symbols are not required.

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3b4 marks

One of the problems associated with the combustion of some fossil fuels is the production of acidic gases, including the oxides of nitrogen and sulfur.

i)
Explain how oxides of sulfur and nitrogen can be formed from the combustion of fossil fuels.
(2)


ii)
Some power stations use a process of flue gas desulfurisation (FGD) to remove sulfur oxides from the gaseous combustion products.
One such process, known as wet scrubbing, uses a mixture of calcium carbonate and water to react with sulfur dioxide.

Two relevant equations are

SO2 (g) + CaCO3 (s) → CaSO3(s) + CO2 (g)

  CaSO3 (s) + 2H2O (l) + 1⁄2O2 (g) → CaSO4·2H2O (s)

Explain why this process is an incomplete solution to the problem of burning fossil fuels.
Use the equations provided to illustrate your answer.

(2)

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3c1 mark

Draw a dot‐and‐cross diagram for sulfur dioxide, showing outer electrons only.

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1a1 mark

This question is about alkanes and their reactions. 

What is the IUPAC name for this alkane? 

q2a-9cho-al-2-june-2019-qp-edexcel-a-level-chem
  ☐ A 4-ethyloctane  
  ☐ B 5-ethyloctane  
  ☐ C 3-propylheptane 
  ☐ D 5-propylheptane 

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1b1 mark

What is the name of the process that could be used to produce propane, C3H8, from decane, C10H22? 

  ☐ A substitution 
  ☐ B reforming  
  ☐ C fractional distillation 
  ☐ D cracking  

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1c
Sme Calculator7 marks

A student researched the reaction of propane with bromine and found that the reaction could be used to make 1-bromopropane.  

text C end text subscript 3 straight H subscript 8 space left parenthesis straight g right parenthesis space plus space Br subscript 2 space left parenthesis straight l right parenthesis space rightwards arrow space straight C subscript 3 straight H subscript 7 Br space left parenthesis straight l right parenthesis space plus space HBr space left parenthesis straight g right parenthesis space
 
i)
The first step of the reaction involves 
(1)
  ☐ A heterolytic bond fission to form free radicals  
  ☐ B heterolytic bond fission to form ions  
  ☐ C homolytic bond fission to form free radicals  
  ☐ D homolytic bond fission to form ions 

ii)

Calculate the atom economy by mass for the formation of 1-bromopropane in the reaction in (c).  

(2)

iii)
A source from the internet gave the percentage yield for this reaction as 31.0%. 
The best explanation for the low percentage yield of 1-bromopropane in this reaction is 

(1)

  ☐ A bromine is very unreactive 
  ☐ B a gaseous reactant always gives a low yield 
  ☐ C the reaction is very slow 
  ☐ D the reaction produces a mixture of organic products 

iv)
Calculate the volume of propane, in dm3, measured at room temperature and pressure, that is needed to produce 14.7 g of 1-bromopropane, assuming a percentage yield of 31.0%.
Give your answer to an appropriate number of significant figures.

[Molar gas volume at r.t.p. = 24.0 dm3 mol-1] 

(3)

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