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Organic Families (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

Exam Questions

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1a2 marks

The alkanes are a family of saturated hydrocarbons. Their reactions include combustion, cracking and substitution.

 
i)
What is meant by the term hydrocarbon?
 
[1]
 
ii)
What is meant by the term saturated?
 
[1]

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1b3 marks
i)
What is the general formula for the homologous series of alkanes?
 
[1]
 
ii)
Calculate the mass of one mole of an alkane with 14 carbon atoms.
 
[2]

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1c4 marks

Cracking is used to obtain short-chain alkanes, alkenes and hydrogen from long-chain alkanes.

 
i)
Give a use for each of the three products listed above.
 
short-chain alkanes ..................................................
 
alkenes ..................................................
 
hydrogen ..................................................
 
[3]
 
ii)
Write an equation for the cracking of decane, C10H22, which produces two different alkenes and hydrogen as the only products.
 
[1]

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2a2 marks

Alkenes are unsaturated hydrocarbons.

i)
State the general formula of alkenes.

[1]

ii)
State the general formula of alkenes.

[1]

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2b2 marks

What is meant by the term unsaturated hydrocarbon?

unsaturated

hydrocarbon 

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2c3 marks

Describe a test that would distinguish between saturated and unsaturated hydrocarbons.

Reagent: 

Observation (saturated hydrocarbon):

Observation (unsaturated hydrocarbon):

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2d4 marks

Extended tier only

Addition polymers can be made from alkenes. The diagram shows part of an addition polymer.

polymer-polybutene

i)
Draw a circle on the diagram to show one repeat unit in this polymer.

[1]

ii)
Give the structure and the name of the monomer used to make this polymer.

[2]

iii)
Give the structure of an isomer of the alkene in (e)(ii).

[1]

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3a4 marks

Natural gas, which is mainly methane, is a fossil fuel.

 
i)
What is meant by the term fuel?
 
[1]
 
ii)
Name two other fossil fuels.
 
[2]
 
iii)
Name a solid fuel which is not a fossil fuel.
 
[1]

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3b4 marks
Fossil fuels are formed by the anaerobic decomposition of organic matter. Anaerobic means in the absence of oxygen.
 
i)
The organic matter contains hydrogen and carbon. Suggest the products that would be formed if the decomposition occurred in the presence of oxygen.
 
[2]
 
ii)
What are the two main disadvantages in the widespread use of fossil fuels?
 
[2]

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4a2 marks

A major source of energy is the combustion of fossil fuels.

i)
Name a solid fossil fuel.
 
[1]
 
ii)
Name a gaseous fossil fuel.
 
[1]

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4b5 marks
Petroleum is separated into more useful fractions by fractional distillation.
 

i)
Name two liquid fuels obtained from petroleum.
 
........................................ and ........................................
 
[2]
 
ii)
Name two other useful products obtained from petroleum that are not used as fuels.
 
........................................ and ........................................
 
[2]
 
iii)
Give another mixture of liquids that is separated on an industrial scale by fractional distillation.
 
[1]

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5a1 mark

Large hydrocarbons can be cracked to form smaller hydrocarbons.
Complete the chemical equation for cracking tridecane, C13H28, to form an alkene and one other hydrocarbon.

C13H28 → C3H6 + ..............

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5b1 mark

Ethene is an alkene.

Draw the structure of ethene showing all of the atoms and all of the bonds.

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6a1 mark

The properties of five alkenes at room temperature are shown in the table.

alkene number of carbon atoms in a molecule state at room temperature density
in g / cm3		 boiling point
/ °C
ethene 2 gas 0.0012 –104
propene 3 gas 0.0018 –47
butene 4 gas 0.0024  
pentene 5 liquid 0.64 30
hexene 6 liquid 0.67 63

Answer these questions using only the information in the table.

Describe the general trend in the density of the alkenes.
 

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6b1 mark
Predict the boiling point of butene.
 

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1a
Sme Calculator2 marks

The alkenes are a series of unsaturated hydrocarbons. They have the general molecular formula CnH2n.

Deduce the molecular formula of an alkene which has a relative molecular mass of 126.

Show your working.

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1b4 marks

This question is concerned with some of the addition reactions of but-1-ene.

 
i)
Name the product formed when but-1-ene reacts with water.
 
[1]
 
ii)
Complete the equation.
 
CH3–CH2–CH=CH2 + Br2 → .....................................................................
 
[2]
 
iii)
Deduce the formula of the compound which reacts with but-1-ene to form 1-iodobutane.
 
[1] 

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2a
Sme Calculator6 marks

The alcohols form a homologous series.

i)
Give three characteristics which all members of a homologous series share.
[3]
ii)
Give the name of the third member of this series.
[1]
iii)
Deduce the molecular formula of the alcohol whose Mr = 158. Show your working.
[2]

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2b6 marks

The alcohols form a homologous series. The first member of this series is methanol, CH3OH.

i)
Give the general formula of the alcohols.

[1]

ii)
The mass of one mole of an alcohol is 116 g. What is its formula?
Show your reasoning.

[2]

ii)
Draw a diagram showing the arrangement of the outer (valency) electrons in one molecule of methanol.

Use x to represent an electron from a carbon atom.
Use o to represent an electron from a hydrogen atom.
Use ● to represent an electron from an oxygen atom.

[3]

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3a5 marks

Alcohols can be made from petroleum by the following sequence of reactions.

alkanes from petroleum → alkene → alcohol

Describe the manufacture of ethanol from hexane, C6H14. Include in your description an equation and type of reaction for each step.

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3b2 marks

One use of ethanol is in alcoholic drinks.

Give two other uses of ethanol.

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4a3 marks

Alkanes and alkenes are both series of hydrocarbons.

i)
Explain the term hydrocarbon.

[1]
ii)
What is the difference between these two series of hydrocarbons?

[2]

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4b1 mark

Extended tier only

Alkenes and simpler alkanes are made from long-chain alkanes by cracking.

Complete the following equation for the cracking of the alkane C20H42.

C20H42  → 2C4H8 + 2C2H4 + ...............

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4c7 marks

Extended tier only

Alkenes such as butene and ethene are more reactive than alkanes.


Alkenes are used in the petrochemical industry to make a range of products, which includes polymers and alcohols.

i)
Dibromoethane is used as a pesticide. Complete the equation for its preparation from ethene.

ethene-bromination

[1]

ii)
The structural formula of a poly(alkene) is given below.
Deduce the structural formula of its monomer.
polybut-2-ene-q-image
[2]

iii)
How is butanol made from butene, CH3 –CH2 –CH=CH2?

Include an equation in your answer.

[2]
iv)
Cracking changes alkanes into alkenes. How could an alkene be converted into an alkane?

Include an equation in your answer.
[2]

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4d4 marks

Extended tier only

20 cm3 of a hydrocarbon was burnt in 175 cm3 of oxygen. After cooling, the volume of the remaining gases was

125 cm3. The addition of aqueous sodium hydroxide removed carbon dioxide leaving 25 cm3 of unreacted oxygen.

Volume of oxygen used = .......... cm3
[1]

Volume of carbon dioxide formed = .......... cm3
[1]

Deduce the formula of the hydrocarbon and the balanced equation for the reaction.
[2]

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5a2 marks

Describe how alkenes, such as but-1-ene, can be made from alkanes.

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5b3 marks

Extended tier only

Name the product formed when but-1-ene reacts with:

 
bromine, ......................................................................................................................
[1]
 
hydrogen, ....................................................................................................................
[1]
 
steam. .........................................................................................................................
[1]

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6a3 marks

The alcohols form a homologous series. Two characteristics of a homologous series are that the physical properties of the members vary in a predictable way and they have similar chemical properties.

Complete the table.

name formula mass of one mole / g boiling point / oC
methanol CH3 –OH 32 64
ethanol CH3 –CH2 –OH 46 78
propan-1-ol CH3 –CH2 –CH2 –OH 60 98
butan-1-ol CH3 –CH2 –CH2 –CH2 –OH 74 118
pentan-1-ol     138
hexan-1-ol CH3 –CH2 –CH2 –CH2 –CH2 –CH2 –OH 102  

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6b2 marks

Give two other characteristics of a homologous series.

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6c3 marks

Draw a diagram showing the arrangement of the valency electrons in one molecule of the covalent compound methanol.

Use x to represent an electron from a carbon atom.
Use ● to represent an electron from an oxygen atom.
Use o to represent an electron from a hydrogen atom.

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7a4 marks

The alkenes are a homologous series of unsaturated hydrocarbons.

The table below gives the names, formulae and boiling points of the first members of the series.

Name Formula Boiling point  / oC
 ethene C2H4 -103.7
 propene C3H6 -47.6
 butene C4H8 -6.3
 pentene C5H10 30
 hexene    

i)
Complete the table by giving the formula of hexene and by predicting its boiling point.

[2]

ii)
Deduce the formula of the alkene which has a relative molecular mass of 168.
Show your working.

[2]

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7b3 marks

Describe a test that will distinguish between the two isomers, but-2-ene and cyclobutane.

test ..............................................................................................................................................................................

result with but-2-ene  ..........................................................................................................................................

result with cyclobutane  ......................................................................................................................................

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7c3 marks

Extended tier only

Alkenes undergo addition reactions.

i)
What class of organic compound is formed when an alkene reacts with water?
[1]

ii)
Draw the structure of the polymer formed from but-2-ene.

[2]

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8a7 marks

Extended tier only

Two homologous series of hydrocarbons are the alkanes and the alkenes.

One general characteristic of a homologous series is that the physical properties vary in a predictable way.

i)
State three other general characteristics of a homologous series.

[3]

ii)
How can the molecular formula of a hydrocarbon show whether it is an alkane or an alkene?

[2]

iii)
How do alkanes and alkenes differ in their molecular structures?
[2]

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8b5 marks

Cracking is the thermal decomposition of alkanes into smaller hydrocarbons and possibly hydrogen.

i)
State two conditions required for the cracking of an alkane.

[2]

ii)
One type of cracking produces an alkane and an alkene.

Complete an equation for the cracking of heptane into an alkane and an alkene.

C7H16 → ................ + ................ 

[1]

iii)
Complete an equation for the cracking of heptane into hydrogen and two other products.

C7H16  →................ + ................ + H2

[1]

iv)
Suggest one reason why cracking is important.
 [1]

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8c2 marks

Extended tier only

Hydrocarbons burn in excess oxygen to form carbon dioxide and water. 20 cm3 of a gaseous hydrocarbon burned in an excess of oxygen, 200 cm3. After cooling, the volume of the residual gas at r.t.p. was 150 cm3, 50 cm3 of which was
oxygen.

i)
Determine the volume of the oxygen used.
[1]

ii)
Determine the volume of the carbon dioxide formed.
[1]

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92 marks

Alkenes are more reactive than alkanes and are used to make a range of organic chemicals. Propene, CH3–CH=CH2, is made by cracking. Give the structural formula of the addition product when propene reacts with the following.

 
i)
water
 
[1]
 
ii)
bromine
 
[1]

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10a3 marks

Alkenes can be made from alkanes by cracking.

i)
Explain the term cracking.

[2]

ii)
One mole of an alkane, when cracked, produced one mole of hexane, C6H14, and two moles of ethene.

What is the molecular formula of the original alkane?

[1]

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10b5 marks

Extended tier only

Alkenes are used in polymerisation reactions and addition reactions.

i)
Draw the structural formula of the product formed by the addition polymerisation of but-2-ene. Its formula is given below.

sfVPdcYZ_but-2-ene

[3]

ii)
Give the name and structural formula of the addition product formed from ethene and bromine.

name ...................................................................................................................................
structural formula

[2]

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10c2 marks

Alkenes are more reactive than alkanes and are used to make a range of organic chemicals. Propene, CH3–CH=CH2, is made by cracking. Give the structural formula of the addition product when propene reacts with the following.

 

i)
water

[1]

 

ii)
bromine

[1]

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12 marks

Extended tier only

Alkenes polymerise to form addition polymers.

Draw the structural formula of poly(cyanoethene), include at least two monomer units.

The structural formula of the monomer, cyanoethene, is given below.

polycyanoethane

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2a2 marks

Complete the following equations for the addition reactions of propene:

i)
CH3–CH=CH2 + Br2 → ....................................
[1]
ii)
CH3–CH=CH2 + H2O → ....................................
[1]

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2b2 marks

Draw the repeat unit of poly(propene).

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2c4 marks

Extended tier only

0.01 moles of an alkene needed 2.4 g of oxygen for complete combustion. 2.2 g of carbon dioxide were formed.

i)
Determine the following mole ratio.
 
moles of alkene : moles of O2 : moles of CO2
 
From this ratio determine the formula of the alkene.
[3]
ii)
Write an equation for the complete combustion of this alkene.

[1]

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3a2 marks

Petroleum is a source of many important chemicals.

Name two industrial processes which must take place to produce alkenes from petroleum.

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3b3 marks

Extended tier only

Ethene, CH2=CH2, and propene, CH2=CHCH3, can both be converted into polymers.

 

i)
What type of polymerisation takes place when ethene forms a polymer?

[1]
ii)
Propene has the structural formula CH2=CHCH3.

Draw two repeat units of the polymer made from propene.
[2]

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4
Sme Calculator4 marks

Extended tier only

The alkanes are generally unreactive. Their reactions include combustion, substitution and cracking.

The complete combustion of an alkane gives carbon dioxide and water.

 
i)
10 cm3 of butane is mixed with 100 cm3 of oxygen, which is an excess. The mixture is ignited. What is the volume of unreacted oxygen left and what is the volume of carbon dioxide formed?
 
C4H10 (g) + 6.5O2 (g) → 4CO2 (g) + 5H2O (l)
 
Volume of oxygen left = .................................................. cm3
 
Volume of carbon dioxide formed = .................................................. cm3
 
[2]
 
ii)
Why is the incomplete combustion of any alkane dangerous, particularly in an enclosed space?
 
[2]

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