Hydrocarbons (Edexcel GCSE Chemistry)

Exam Questions

2 hours18 questions
1a1 mark

Hydrocarbons are organic molecules. Alkanes and alkenes are families of hydrocarbons

Which statement correctly describes the alkanes?

  A Alkanes are saturated hydrocarbons
  B Alkanes are unsaturated hydrocarbons
  C Alkanes contain hydrogen, carbon and oxygen atoms
  D Alkanes contain a carbon-carbon double bond
1b1 mark

What is the correct general formula of an alkane?

  A CH4
  B CnH2n
  C CH2n 
  D CnH2n+2
1c2 marks

Hydrocarbons undergo combustion in the presence of air.

Name two products formed when a hydrocarbon undergoes complete combustion. 

1d2 marks

Propane is an alkane that contains three carbon atoms. Draw the displayed formula of propane.

Did this page help you?

2a2 marks

Figure 1 shows the structure of an alkane and an alkene. 

Figure 1 
aqa-gcse-7-1e-tq4a-alkane-alkene

Give two differences between an alkane and an alkene.

2b2 marks

To distinguish between alkanes and alkenes, bromine water can be added. 

Draw one line from each hydrocarbon to give the colour change that would be observed if bromine water was added.

 screen-shot-2023-01-25-at-08-34-52
2c1 mark

What is the general formula for alkenes?

2d2 marks

Draw the structure of propene.

Did this page help you?

3a1 mark

The structure of one molecule of compound is shown in Figure 1. 

edx-9-2e-q3a-propane

Figure 1

What is the molecular formula of the compound in Figure 1?

  A C3H6
  B CH
  C CH6
  D 3C6H
3b3 marks

State why the compound is described as an unsaturated hydrocarbon. 

  •  Unsaturated  .......................................................................................................................

(1)

  • Hydrocarbon .......................................................................................................................

(2)

3c2 marks

Here are five statements about the reactions of alkenes. 

Place ticks in boxes by the two statemetns that are correct.

 Alkenes react with bromine water to form an unsaturated compound  
 Alkenes react with oxygen to form carbon dioxide and hydrogen   
 Alkenes react with bromine water in a substitution reaction  
 Alkenes react with bromine water to form a colourless solution  
 Alkenes undergo complete and incomplete combustion  
3d1 mark

Both alkenes and alkanes undergo combustion reactions. 

What type of reaction is combustion?

  A Thermal decomposition
  B Oxidation
  C Addition
  D Neutralisation

Did this page help you?

4a1 mark

Alkenes are unsaturated hydrocarbons 

The displayed formula of an alkene is shown in Figure 1.

butene

Figure 1 

Name the alkene shown in Figure 1. 

4b1 mark

The carbon and hydrogen atoms in Figure 1 are joined together by chemical bonds. 

Name the type of bond that forms between the atoms.

  A Ionic 
  B Metallic
  C Covalent 
  D Hydrogen

4c2 marks

When the substance in Figure 1 reacts with oxygen, carbon dioxide and water are formed. 

Describe and give the result for a test that would show the presence of carbon dioxide. 

4d1 mark

Alkenes can be formed from the cracking of long chained hydrocarbons. 

What type of reaction is cracking?

  A Thermal decomposition
  B Combustion
  C Neutralisation
  D Oxidation

Did this page help you?

5a1 mark

Figure 1 shows one molecule of a compound obtained from crude oil. 

ethane-structural-formula

Figure 1

Give the names of the two elements in this molecule.

5b1 mark

What is the molecule in Figure 1? 

  A a halide
  B a fullerene
  C a chain molecule
  D a ring molecule
5c2 marks

The substance in Figure 1 can undergo combustion reactions.

Use words from the box to complete the sentences about complete combustion.

 hydrogen              water             oxygen                 air                    carbon monoxide        

During combustion, the substance reacts with a plentiful supply of  ______________________. 

The products of the reaction are carbon dioxide and  ________________________. 

5d1 mark

What is the relative formula mass of the compound in Figure 1? 

(relative atomic masses: H = 1.0, C = 12)

  A 13
  B 28
  C 30
  D 44

Did this page help you?

11 mark

Heptane is an alkane with seven carbons.

What is the chemical formula of heptane?

  A C7H10
  B C7H12
  C C7H14
  D C7H16

Did this page help you?

2a1 mark

Alkanes and alkenes are hydrocarbons.

The structure of a molecule of butane is shown.

Butane Displayed Formula

Which of the following is the empirical formula for butane?
  A CH
  B CH2
  C C2H5
  D C4H10

2b1 mark

The graph in Figure 13 shows the boiling points of some alkanes plotted against the number of carbon atoms in one molecule of each alkane.

fig-13-q9b-1cho-2f-specimen-2018

Figure 13

A molecule of pentane contains five carbon atoms.

Use the graph to estimate the boiling point of pentane.

boiling point of pentane = .............................................................. °C

2c2 marks

Figure 14 shows some information about the alkenes, ethene and propene.

Complete the table. The structure of propene must show all covalent bonds.

name of alkene molecular formula structure
ethene   ethene-q-image
propene C3H6  

2d1 mark

Alkenes burn completely to produce carbon dioxide and water.


Balance the equation for the complete combustion of butene gas, C4H8.

C4H8 + .......... O2 → .......... CO2 + .......... H2

2e
Sme Calculator
4 marks

Butene reacts with steam to produce butanol.

C4H8 + H2O → C4H9OH

i)
Calculate the maximum mass of butanol, C4H9OH, that can be produced when 1.4 kg of butene, C4H8, reacts with excess steam.

(relative atomic masses: H = 1, C = 12, O = 16
relative molecular mass of butene, C4H8 = 56)

(3)

mass of butanol = .............................................................. kg

ii)
What type of reaction takes place between butene and steam?
(1)
  A addition
  B dehydration
  C neutralisation
  D substitution

2f2 marks

A sample of each of three hydrocarbons, X, Y and Z, was shaken with bromine water. Bromine water is orange coloured.

The results are:

X orange mixture becomes colourless
Y orange mixture becomes colourless
Z mixture remains orange

Using the results, comment on the structures of the hydrocarbons X, Y and Z.

2g1 mark

Alkenes are used to make polymers.

Figure 15 shows the repeating unit of a polymer.

fig-15-q9g-1cho-2f-specimen-2018

Figure 15

Draw the structure of a molecule of the monomer that was used to produce this polymer.

2h1 mark

Bottles can be made of polymers, such as poly(ethene), and of glass.

Give one advantage of a bottle made of a polymer rather than a bottle made of glass.

Did this page help you?

31 mark

Which of the following shows the product of the reaction between propene and bromine?

  A k41Locp-_option-a

  B DdhOC04d_option-b

  C MaGJ4-6N_option-c

  D BVbVRCN8_option-d

Did this page help you?

4a1 mark

Figure 8 shows one molecule of each of four different substances, A, B, C and D.

fig-8-q6-1cho-2f-paper-1-june-2018

Figure 8

State the formula of a molecule of substance B.
4b2 marks
i)
Substance C can be formed by burning an element in oxygen.

Write the word equation for this reaction.

(1)

ii)
Consider substances A, B, and D.

Give the letters of the two substances that can be formed by burning an element in oxygen.

(1)

4c2 marks

The amount of oxygen in the atmosphere has increased since the Earth’s early atmosphere was formed.

Explain what has caused this change.

4d2 marks

Carbon dioxide is present in the Earth’s atmosphere.

Some processes increase the amount of carbon dioxide in the atmosphere, other processes decrease it.

Draw one straight line from each change in the amount of carbon dioxide in the atmosphere to the process causing the change.

fig-q6d-1cho-2f-paper-1-june-2018
4e4 marks

Figure 9 shows a graph of the amount of carbon dioxide in the Earth’s atmosphere from 1985 to 2005.

fig-9-q6e-1cho-2f-paper-1-june-2018
i)
Describe how the amount of carbon dioxide in the Earth’s atmosphere varies within each year.
(1)
ii)
Describe the overall trend in the amount of carbon dioxide in the Earth’s atmosphere from 1985 to 2005.
(1)
iii)
Calculate the change in the amount of carbon dioxide in the Earth’s atmosphere from the beginning of 1990 to the beginning of 2000.

(2)

change in amount = .................................... ppm

Did this page help you?

51 mark

Which of the following molecules is an alkene?

  A C6H10
  B C4H10
  C C5H10
  D C6H14

Did this page help you?

6a3 marks

Propene can be produced by the cracking of some hydrocarbons obtained from crude oil.

 The equation shows the cracking of one molecule of decane to produce one molecule of butene and one molecule of another product.

 
C10H22  →  C4H8 + CxHy
decane    butene
 
 
i)
Calculate the values of x and y in CxHy.
 
(2)
 
ii)
State the total mass of products formed if 25 g of decane is cracked in this way.
 
(1)
6b2 marks

The structure of a molecule of ethene is shown in Figure 8.

 
fig-8-q5b-1cho-2f-paper-1-june-2019
 
Figure 8
 
i)
Figure 9 shows the incomplete dot and cross diagram for a molecule of ethene.
 
fig-9-q5bi-1cho-2f-paper-1-june-2019
 
Figure 9
 
Complete Figure 9 to show the electrons of the C C double bond.
 
(1)
 
ii)
The incomplete combustion of ethene in air produces water as one of the products.
 
Give the name of another product of the incomplete combustion of ethene.
 
(1)
6c2 marks

Substance X is an unsaturated hydrocarbon.

 The structure of a molecule of substance X is shown in Figure 10.

 
fig-10-q5c-1cho-2f-paper-1-june-2019
 
Figure 10
 

Explain how the structure of substance X shows that it is an unsaturated hydrocarbon.

6d2 marks

Two liquid hydrocarbons, A and B, were tested with bromine water.

One hydrocarbon was known to be an alkane.

The other hydrocarbon was known to be an alkene.

Each hydrocarbon was shaken with a few drops of bromine water.

 The results of the tests were

   hydrocarbon A + bromine water: the mixture turned from orange to colourless.
   hydrocarbon B + bromine water: the orange colour remained.

Explain these results.

 

Did this page help you?

71 mark

The complete combustion of pentane, C5H12, takes place in the following unbalanced equation:

_C5H12   +   _O2 →   _CO2   +  _H2O

What numbers will balance the reaction?

A 1,4,5,3
B 1,8,5,6
C 2,8,5,6
D 2,4,5,6

Did this page help you?

8a2 marks

Ethene, C2H4, is an unsaturated hydrocarbon.

Explain why ethene is an unsaturated hydrocarbon.
8b3 marks

A sample of ethene is burned completely in oxygen.

Write the balanced equation for this reaction.

8c3 marks

Ethene can be polymerised to form poly(ethene).

Describe what you would see when a sample of ethene and a sample of poly(ethene) are shaken with separate, small volumes of bromine water.

8d
Sme Calculator
3 marks

A different hydrocarbon has a relative formula mass of 84.
It has an empirical formula of CH2.

Deduce the molecular formula of this hydrocarbon.

You must show your working.
(relative atomic masses : H=1, C=12)

Did this page help you?

91 mark

Bromine water is an orange-brown solution.

When shaken with bromine water, which of the following compounds would cause the solution to decolourise?

  A C3H8
  B C9H20
  C C6H16
  D C4H8

Did this page help you?

1a
Sme Calculator
4 marks

Higher Only

Hydrogen reacts with oxygen to form steam.

2H2 (g) + O2 (g) rightwards arrow 2H2O (g)

Bond energies are shown in Figure 14.

bond bond energy in kJ mol−1
straight H long dash straight H 435
straight O equals straight O 500
straight O long dash straight H 460

Figure 14

Calculate the energy change for the reaction of 2 mol of hydrogen gas, H2, with 1 mol of oxygen gas, O2, to give 2 mol of steam, H2O.

energy change = .............................. kJ mol-1

1b6 marks

A student is provided with unlabelled samples of three liquids.

The three liquids are known to be:

hexane, C6H14, a liquid alkane
hexene, C6H12, a liquid alkene
butanoic acid, C4H8O2, a carboxylic acid, in aqueous solution

Aqueous solutions of carboxylic acids contain hydrogen ions and undergo reactions typical of acids with indicators and carbonates.

Describe, in detail, using the information given and your knowledge of the reactions of these liquids, tests the student should carry out to identify each of the three liquids.

You should include balanced equations for any chemical reactions described.

Did this page help you?

2a2 marks

This question is about the reactions of alkanes.

Decane can be cracked to form heptane and one other product in the following reaction:

C10H22   →   C7H16   + ____________

Name and draw the displayed formula of the other product formed.

2b3 marks

Describe and give the result of a chemical test that would distinguish between the two products.

2c2 marks

Explain why decane is a saturated hydrocarbon.

2d2 marks

Another alkane, butane, can undergo the following combustion reactions:

   Equation 1:  2C4H10 + 13O2 ⟶ 8CO2 + 10H2

   Equation 2:     2C4H10 + 5O2 ⟶ 8C + 10H2

Explain why different products are made.

Did this page help you?

3a1 mark

Alkanes can be obtained from the fractional distillation of crude oil.

Figure 1 shows some alkanes that are found in crude oil.

Alkanes Boiling point in oC
 C5H12 36
C7H16 98
C10H22 174

Figure 1


What is the general formula for alkanes?

3b2 marks

Write the balanced symbol equation for the complete combustion of C7H16

3c3 marks

Explain the trend in boiling points of the alkanes.

3d2 marks

A student was investigating the properties of the alkanes shown in Figure 2 in part (a) using the following method:

1) Pour 20 cm3 of C5H12 into a funnel 

2) Open the tap and start a stopwatch 

3) When the level of C5H12 reaches line X stop the stopwatch 

4) Repeat steps with the other two alkanes 

The diagram in Figure 2 shows the apparatus used.

 

hydrocarbon-viscosity-experiment

Figure 2

C5H12 took 5.3 seconds to reach line X.

Explain the trend you would expect to see when the student repeats the method with the other two alkanes.

Did this page help you?

4a1 mark

Cracking is used break long chain hydrocarbons down into small more useful hydrocarbons. 

Figure 1 shows the reaction that occurs when a long chain hydrocarbon, C18H38 undergoes cracking. 

C18H38       →       C11H24     +      C3H6      +       2C2H

compound  W         compound X   compound Y    compound Z      

Figure 1 

Give the empirical formula of compound W.

4b2 marks

Write a balanced symbol equation for the incomplete combustion of compoundto produce carbon monoxide and water.

4c2 marks

Compound Y undergoes a reaction with bromine water. 

i)
Draw the displayed formula of the product formed during this reaction.

(1)

ii)
Give one observation you would make during this reaction. 

(1)

4d4 marks

Compare the structures and bonding of compounds X and Y

Did this page help you?