AQA AS Chemistry

Topic Questions

3.2 Alkanes

11 mark

A fraction of distilled crude oil contains molecules with between 15 and 19 carbon atoms. This fraction is cracked by strong heating.

Why is this fraction cracked?

 

To produce alkenes

To produce smaller molecules which are in higher demand

To insert oxygen atoms into the hydrocarbons

A

B

 

C

 

D

   

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21 mark

The hydrocarbon C17H36 can be cracked.

Which compound is the least likely to be produced in this reaction?

  • C16H34

  • C8H16

  • C4H8

  • C3H8

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31 mark

In the presence of ultraviolet light, ethane and chlorine react to give a mixture of products.

Which compound could be present in the mixture of products?

  • CH3CH2CH2CH2CH3

  • CH3CH2CH2CH3

  • CH3CH2CH2Cl

  • CH3Cl

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41 mark

Which hydrocarbon would not be collected in the inverted tube by heating pentane, CH3(CH2)3CH3, in the apparatus shown?

q4-easy-3-2-alkanes

  • CH3(CH2)8CH3

  • CH3CH2CH=CH2

  • CH3CH3

  • CH4

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51 mark

Ultraviolet light initiates the following reaction.

alkane + chlorine → chloroalkane + hydrogen chloride

What happens to chlorine in this photochemical reaction?

  • heterolytic fission to give an electrophile

  • homolytic fission to give an electrophile

  • heterolytic fission to give a positive and negative ion

  • homolytic fission to give free radicals

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61 mark

Which of the following products are possible from the incomplete combustion of alkanes?

 

Carbon

Carbon monoxide

Hydrogen 

A

 

B

 

C

 

D

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71 mark

The combustion of fossil fuels results in the release of pollutant gases.

Which row correctly describes the environmental problems associated with the pollutant gases?

 

Sulfur dioxide

Nitrogen oxides

Carbon particulates

A

Acid rain

Global warming

Global warming

B

Global warming

Acid rain

Global dimming

C

Acid rain

Acid rain

Global dimming

D

Global warming

Global dimming

Acid rain

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81 mark

Fractional distillation is used to separate the hydrocarbon mixture of crude oil by boiling point.

Which is the correct description of the fractional distillation process?

  • Fractional distillation is a physical process that breaks the hydrocarbon covalent bonds

  • Fractional distillation is a chemical process that breaks the hydrocarbon covalent bonds

  • Fractional distillation is a physical process that overcomes the intermolecular forces between hydrocarbon molecules

  • Fractional distillation is a chemical process that overcomes the intermolecular forces between hydrocarbon molecules

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91 mark

Which equation is correct for the complete combustion of heptane?

  • 2C7H16 + 22O2 → 14CO2 + 16H2O

  • 2C7H16 + 15O2 → 14CO + 16H2O

  • 2C7H14 + 21O2 → 14CO2 + 14H2O

  • 2C6H14 + 19O2 → 12CO2 + 14H2O

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101 mark

Ethane reacts with bromine in the presence of ultraviolet light to form bromoethane and hydrogen bromide.

C2H6 + Br2 → C2H5Br + HBr

Which equation represents the desired termination step for this reaction?

  • C2H5 + Br2 → C2H5Br + Br

  • C2H5 + Br → C2H5Br

  • Br2 → 2Br

  • 2C2H5 → C4H10

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11 mark

The petrol additive tetraethyl-lead(IV), Pb(C2H5)4, is now banned in many countries. 

When it is completely burned in air, lead(II) oxide, CO2 and H2O are formed.

How many moles of oxygen are required to burn one mole of Pb(C2H5)4?

  • 9.5

  • 11

  • 13.5

  • 27

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21 mark

Nitric oxide, NO, reacts with octane in the catalytic converter of a car to create three non-toxic products.

What are the whole number coefficients in the balanced equation for this reaction?

  • 34 : 17

  • 50 : 25

  • 2 : 1

  • 24 : 12

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31 mark

The cracking of eicosane, C20H42, produces a hydrocarbon that is in very high demand for transportation and also three consecutive members of the same homologous series of hydrocarbons.

What are the correct products of cracking for the given reaction?

  • Butene, octane, pentene, propene

  • Butane, butene, hexene, octane

  • Ethane, hexene, heptene, pentene

  • Ethene, hexane, heptene, pentene

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41 mark

Unburnt hydrocarbons from fuels can be oxidised to carbon dioxide and water in the catalytic converter of a car.

What is the correct coefficient to balance the oxidising agent, [O], in this reaction?

CnH2n+2   +    _[O]    →    nCO2    +     (n+1)H2O

  • n+2

  • 2n+2

  • 2n+1

  • 3n+1

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51 mark

Which statement about cracking is correct?

  • Thermal cracking occurs at high temperatures in the presence of zeolites to produce a high percentage of alkenes

  • Thermal cracking occurs at high temperatures and high pressures to mainly produce motor fuels and aromatic hydrocarbons

  • Catalytic cracking occurs at high temperatures in the presence of zeolites to mainly produce motor fuels and aromatic hydrocarbons

  • Catalytic cracking occurs at high temperatures and high pressures to produce a high percentage of alkenes

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61 mark

Ethane reacts with bromine in the presence of ultraviolet light to form dibromoethane and hydrogen bromide.

The reaction proceeds via free radical substitution involving initiation, propagation and termination steps.

What is the minimum number of free radical mechanism steps to produce dibromoethane?

  • 5

  • 6

  • 7

  • 8

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71 mark

Ethane reacts with chlorine in the presence of ultraviolet light to form trichloroethane and hydrogen chloride.

The reaction proceeds via free radical substitution involving initiation, propagation and termination steps.

Which propagation equation is involved in the free radical reaction to form trichloroethane?

  • C2H6 + Cl → C2H6 + HCl 

  • C2H3Cl2 + Cl → C2H3Cl3 + H

  • C2H5 + Cl2 → C2H5Cl  + Cl

  • C2H4Cl + Cl2 → C2H4Cl2 + Cl

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81 mark

Ethane reacts with bromine in the presence of ultraviolet light to form tribromoethane and hydrogen bromide.

The reaction proceeds via free radical substitution involving initiation, propagation and termination steps.

Which equation represents a possible termination step in this reaction?

  • 2C2H4  → C4H8

  • C2H4Br + C2H5 → C4H9Br

  • C2H4 + C2H3Br → C4H7Br

  • C2H3Br2 + C2H3Br → C4H6Br3

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91 mark

Heptane and octane can be separated in the school laboratory.

Which statement about the separation of a mixture of heptane and octane is correct?

  • Fractional distillation is used because the mixture is vapourised and the temperature gradient in the fractionation column allows the mixture to separate by boiling point

  • Octane will distil first as the strength of the van der Waals forces is weaker resulting in a lower boiling point

  • Heptane will distil first as the strength of the van der Waals forces is weaker resulting in a lower boiling point

  • Simple distillation is used because the mixture is vapourised and the temperature gradient in the fractionation column allows the mixture to separate by boiling point

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101 mark

The cracking of hexadecane, C16H34, can produce heptane, cyclohexane and propene.

Which of the following is the correct information for the cracking described?

 

Type of cracking

Temperature / K

Pressure / kPa

Catalyst

A

Catalytic

1000

100

Zeolite

B

Catalytic

700

250

Aluminosilicate

C

Thermal 

1500

7000

Aluminium oxide

D

Thermal 

700

250

Silicon dioxide

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11 mark

Which equation represents a valid propagation step in the free radical reaction between ethane and bromine?

  • C2H6 + Br → C2H5Br + H

  • C2H5 + Br → C2H5Br 

  • C2H5Br + Br → C2H4Br + HBr

  • C2H5Br + H → C2H5 + HBr

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21 mark

Nitrogen oxide, NO, reacts with octane in the catalytic converter of a car to create non-toxic products.

Which equation correctly represents this reaction?

  • C8H18 + 17NO → 8CO + 8.5N2 + 9H2O

  • C8H18 + 25NO → 8CO2 + 12.5N2 + 9H2O

  • C8H16 + 16NO → 8CO + 8N2 + 8H2O

  • C8H16 + 24NO → 8CO2 + 12N2 + 8H2O

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31 mark

Isooctane, shown below, can be added to fuels for improved performance.

q3-medium-mcq-alkanes







Which is the correct equation for the complete combustion of isooctane?

  • C8H18 + 8½O2 → 8CO + 9H2O

  • C8H18 + 12½O2 → 8CO2 + 9H2O

  • C7H16 + 11O2 → 7CO2 + 8H2O

  • C8H18 + 13O2 → 8CO2 + 9H2O

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41 mark

Sulfur dioxide, SO2, is a pollutant that can be produced during the combustion of impurities in hydrocarbon based fuels.

Which of the statements is correct?

  • Sulfur dioxide does not dissolve in water

  • Sulfur dioxide is responsible for global dimming

  • Sulfur dioxide is an acidic gas

  • Sulfur dioxide can be removed from flue gases by reacting them with magnesium carbonate

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51 mark

Which of these organic compounds would undergo free radical substitution?

 

ethane

fluoroethane

ethene

ethanal

A

B

 

C

   

D

   

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61 mark

Which is the correct balanced symbol equation for the cracking of eicosane, C20H42?

  • C20H42 + 30½O2 → 20CO2 + 21H2O

  • C20H42 → C8H16 + C6H12 + 2C3H6

  • C20H42 → C8H16 + 2C5H10 + C2H6

  • C20H42 → C7H16 + C6H14 + C4H10 + C3H8

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71 mark

Low demand, long chain hydrocarbons can be cracked into high demand, shorter chain hydrocarbons. This can be done by thermal or catalytic cracking.

Which of the statements about catalytic cracking is correct?

  • Catalytic cracking occurs at temperatures between 750 and 1200K

  • Catalytic cracking occurs in the presence of oxygen

  • Catalytic cracking occurs at pressures 7000 kPa

  • Catalytic cracking produces branched alkanes, cycloalkanes, aromatic compounds and alkenes

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81 mark

Bitumen, diesel, liquified petroleum gases (LPG) and petrol are four of the fractions obtained by the fractional distillation of crude oil.

Which is the correct order of these fractions from lowest to highest boiling point?

  • Liquified petroleum gases (LPG), petrol, diesel, bitumen

  • Bitumen, diesel, liquified petroleum gases (LPG), petrol

  • Liquified petroleum gases (LPG), petrol, bitumen, diesel

  • Bitumen, diesel, petrol, liquified petroleum gases (LPG)

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91 mark

Which of the following statements about the cracking of hydrocarbons is correct?

  • Thermal cracking occurs at high temperature, high pressure and in the presence of a zeolite catalyst

  • Catalytic cracking involves the formation of free radical intermediates

  • Thermal and catalytic cracking are used to convert low demand long chain hydrocarbons into high supply short chain hydrocarbons

  • Catalytic cracking is used to produce mainly motor fuels and aromatic hydrocarbons

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101 mark

Which statement about crude oil fractional distillation is not correct?

  • The fractional distillation column has a negative temperature gradient

  • Each fraction contains a mixture of hydrocarbons

  • Gaseous fractions are formed by overcoming intermolecular forces

  • More volatile fractions are found at the bottom of the fractional distillation column

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