Alkenes (Edexcel IGCSE Science (Double Award): Chemistry)

Which of the following molecules is an alkene?

This question is about alkenes and alkanes.

Complete the table by giving the missing information about the alkene with the molecular formula C₃H₆

Alkenes are unsaturated compounds.

i) State what is meant by the term unsaturated.

(1)

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

(2)

When the alkane methane reacts with chlorine, the products are chloromethane (CH₃Cl) and hydrogen chloride gas.

i) Give a chemical equation for this reaction.

(1)

ii) What is the name of this type of reaction?

(1)

iii) State the condition needed for this reaction to occur.

(1)

When ethane reacts with chlorine, one of the products of the reaction has the formula C₂H₄Cl₂ There are two isomers with this formula.

i) State what is meant by the term isomers.

(2)

ii) Draw the displayed formulae of the two isomers with the formula C₂H₄Cl₂

(2)

Bromine water is an orange-brown solution.

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

Ocimene is an organic compound that gives some plants their particular smell.

The molecular formula of ocimene is C₁₀H₁₆

Calculate the relative formula mass (M_r) of ocimene.

 M_r = ..............................

Using ocimene as an example, explain what is meant by the term empirical formula.

The displayed formula of ocimene is

Explain why ocimene is described as an unsaturated hydrocarbon.

Ocimene is an alkene.

 i) Which of these types of reaction occurs between ocimene and bromine? 

(1)

 ii) Many alkenes have the general formula C_nH_2n

 Suggest why ocimene does not have this general formula.

 (1)

Ocimene can take part in combustion reactions. 

Complete the equation for the complete combustion of ocimene.

C₁₀H₁₆ + .......... O₂ → .............................. + ..............................

Two different products can form during the incomplete combustion of ocimene. 

One product is a solid and the other is a poisonous gas.

 i) Identify these two products.

 (2)

 ii) State why the gas produced is poisonous.

 (1)

The structures of some organic compounds are shown below. 

Compound R can be converted to compound T by reacting it with bromine. 

What kind of reaction is this?

The displayed formula of alkene Y is shown below:

What is the name of alkene Y?

Name the product formed from the reaction between ethene and chlorine. 

The table shows the structures of six organic compounds.

i) Give the letter of a compound not shown as a displayed formula.

 (1)

 ii) Give the letter of a saturated compound with the general formula C_nH_2n

 (1)

 iii) Name compound E.

 (1)

 iv) Explain why compound A and compound D are isomers.

 (2)

Compound F reacts with bromine in the presence of ultraviolet radiation.

 i) Complete the equation for the reaction.

 (1)

   CH₄ + Br₂ →

 ii) Give the name of this type of reaction.

 (1)

i) Another compound, G, has this percentage composition by mass.

 C = 37.8%   H = 6.3%   Cl = 55.9%

 Show by calculation that the empirical formula of compound G is C₂H₄Cl

 (3)

 ii) The relative formula mass (M_r) of G is 127

 Determine the molecular formula of G.

 (2)

 molecular formula = ..............................

Compound E is used to make an addition polymer.

 i) Complete the equation to show part of the polymer formed from two molecules of compound E.

 (2)

 ii) Give one problem caused by the disposal of addition polymers.

  (1)