Introduction (Edexcel IGCSE Chemistry): Exam Questions

Ethene (C₂H₄) can be converted into chloroethene (C₂H₃Cl) in a two-stage process.

The first stage is to convert ethene into 1,2-dichloroethane, C₂H₄Cl₂  

Ethene is reacted with hydrogen chloride and oxygen. 

Complete the chemical equation for this reaction.

.......... C₂H₄ + .......... HCl + .......... O₂ → .......... C₂H₄Cl₂ + .......... H₂O

In the second stage, 1,2-dichloroethane is converted into chloroethene. 

C₂H₄Cl₂ → C₂H₃Cl + HCl 

This is a thermal decomposition reaction. 

State what is meant by the term thermal decomposition.

The diagram shows the displayed formula of chloroethene.

 i) State why chloroethene is described as an unsaturated compound.

(1)

 ii) Describe a test to show that chloroethene is unsaturated.

 (2)

Name the polymer formed from chloroethene.

The structures of six organic compounds are shown.

Which two compounds are isomers of one another?

Which of the following reactions is an example of an addition reaction?

This question is about organic compounds.

Propane is the third member of the homologous series of alkanes.

i) State the name of the third member of the homologous series of alkenes.

(1)

ii) Explain why propane and the third member of the homologous series of alkenes do not have similar chemical properties.

(1)

Propene is bubbled through bromine water until there is no further colour change.

 i) Give the chemical equation for this reaction.

 (1)

 ii) How does the observation support that this is an addition reaction?

(2)

In industry, ethene is reacted with steam to form ethanol.

 i) Using structural formulae, give the chemical equation for this reaction. 

(1)

 ii) State the temperature and pressure required for this reaction.

 (2)

Ethanol oxidises slowly in air to form a chemical that is a member of a different homologous series and has a bitter smell.

 i) State the homologous series to which the oxidation product belongs.

 (1)

 ii) Give the empirical and molecular formulae of the oxidation product.

 (2)

The alcohols form a homologous series with the general formula C_nH_2n+1OH.

The first five members of the homologous series are given in the table below.

 i) Complete the table. 

 (1)

 ii) Complete the equation for the reaction of butan-1-ol in excess oxygen.

 C₄H₉OH + .......O₂ → ..................... + .....................

 (2)

 iii) What is the name of the type of reaction occurring between butan-1-ol and oxygen?

 (1)

State three characteristics of a homologous series other than the variation of physical properties down the series.

There are four isomers with the molecular formula C₄H₉OH that are alcohols. 

These are the displayed formulae of the isomers.

 i) Explain why they are isomers.

 (2)

 ii) Draw the displayed formula of the fourth isomer.

 (1)

An alcohol has this percentage composition by mass.

C = 60.0%       H = 13.3%       O = 26.7%

i) Show by calculation that the molecular formula of the alcohol could be C₃H₈O.

(3)

ii) Explain why the empirical formula is also the molecular formula of the alcohol.

 (1)

The formulas for four organic compounds are given in the table below.

Write the names of each of the compounds.

CH₃CH₂CH₂OH undergoes a combustion reaction in excess oxygen. Write a balanced symbol equation for this reaction. 

Compound A has an M_r of 102 and contains the same functional group as CH₃CH₂CH₂OH. Calculate the percentage by mass of carbon in compound A.

(A_r: O = 16, C = 12, H = 1)

Draw the displayed formula of CH₃CH₂CH₂NH₂

Compound X is a hydrocarbon with an M_r of 70 that contains 85.7% by mass of carbon. When bromine water is added to compound X it remains orange. 

Calculate the molecular formula of compound X

Using the information in part a), determine the structure of compound X.

Compound X reacts with chlorine in the presence of ultra-violet light. Write the equation for this reaction.

Alkanes and alkenes are examples of hydrocarbons.

i) What is meant by the term hydrocarbon?

(1)

ii) Give the general formula of straight-chain

alkanes.

alkenes. 

(2)

A compound X contains carbon, hydrogen and oxygen only.

X contains 54.54% of carbon by mass, 9.09% of hydrogen by mass and 36.37% of oxygen by mass.

i) Calculate the empirical formula of compound X.

(2)

ii) Compound X has a relative molecular mass of 88.

Deduce the molecular formula of compound X.

(2)

An ester has the molecular formula C₃H₆O₂. Name and give the structural formulae of two esters with the molecular formula C₃H₆O₂.

Name the ester produced from the reaction of propanoic acid and methanol.

A polyester is represented by the structure shown.

i) What type of polymerization is used for the production of polyesters?

(1)

ii) Which simple molecule is removed when the polyester is formed?

(1)

iii) Complete the diagrams below to show the structures of the monomers used to produce the polyester. Show all atoms and bonds.

(2)

There is a number of compounds with the molecular formula C₄H₈.

Explain how more than one compound can have the same molecular formula.

Draw the displayed formulae of two isomers with the formula C₄H₈ that belong to different homologous series.

i) Describe a chemical test to show that compounds with the molecular formula C₄H₈ belong to different homologous series.

 (3)

 ii) Explain how the results of the chemical test in part (i) proves that compounds with the molecular formula C₄H₈ belong to different homologous series.

 (1)

Some organic compounds with the molecular formula C₄H₈ can be hydrated to form alcohols.

i) Give a chemical equation for this reaction.

(1)

ii) State the name of this type of reaction.

 (1)

The diagram shows the formulae of some organic compounds.

i) Explain which compound is not a hydrocarbon.

 (1)

 ii) Explain which compounds are shown as displayed formulae.

(1)

An example of the reaction of compound B with a halogen is shown.

 C₄H₁₀ + Cl₂ → C₄H₉Cl + compound G

 i) State the condition needed for this reaction to occur

 (1)

 ii) Deduce the formula of compound G.

 (1)

Compound D undergoes combustion to form a toxic colourless gas, a brown gas and one other product.

 i) Give a chemical equation for this reaction.

 (2)

 ii) Explain how the toxic colourless gas affects the respiratory system. 

 (2)

Compound H belongs to the same homologous series as compound A. 

The complete combustion of one mole of compound H burns is represented by the equation 

compound H + x O₂ → y CO₂ + z H₂O 

The numbers x, y and z are used to balance the equation.

 i) One mole of compound H burning completely in oxygen produces 308 g of carbon dioxide and 144 g of water.

 Calculate the values of y and z.

 [M_r of CO₂ = 44, M_r of H₂O = 18]

 (2)

 y = ..........

 z = ..........

 ii) Determine the molecular formula of the compound H and the value of x.

 (2)

molecular formula = .......... 

x = ..........