COSHH
1/2
Test Tube Reactions of Alkanes
Homolgous series in organic chemistry are made up of compounds with very similar chemical
properties. In fact, it is often the case that if you know the reactions of one of the members, you
can predict the reactions of the others. This experiment will test this hypothesis and will also be
used to compare this series of compound with another in a future session.
Hexane :
Heptane :
Dilute sodium Hydroxide :
Dilute sulphuric acid :
Other points : All waste in designated container.
You will need:
Safety glasses
Test tube rack
Crucible lid
Heat proof mat
Dil. Sodium hydroxide
Lab coat
Test tube holder
Dropping pipette
Hexane
Dil. Sulphuric acid
Test Tubes
Crucible tongs
Bunsen Burner
Heptane
Test #1:
Take a few drops of the alkane on a crucible lid and light it with a
wooden splint.
Observation:
…………………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………….
Test #2:
(Remember to dispose of liquids in the fume hood). Put a few drops of
the alkane in a test tube and carefully add dilute sulphuric acid,
stopper and shake.
Observation:
…………………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………….
Test #3:
Put a few drops of the alkane in a test tube and carefully add dilute
sodium hydroxide, stopper and shake.
Observation
:…………………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………….
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COSHH
1/2
Test Tube Reactions of Alkenes
Cyclohexane :
Cyclohexene :
Conc. sulphuric acid :
Bromine solution:
Potassium Manganate(VII) solution:
Other points : All waste in designated container.
You will need:
Safety glasses
Test tube rack
Crucible tongs
Cyclohexane
Bromine solution
Lab coat
Test Tubes
Test tube holder
Rubber bungs
Crucible lid
Dropping pipette
Cyclohexene
Conc. Sulphuric acid
Potassium Manganate(VII) solution
Test #1:
Take a few drops of the cyclohexane on a crucible lid and light it with a
wooden splint (repeat with cyclohexene).
Observation:
…………………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………….
Test #2:
(Remember to dispose of liquids in the fume hood). Put a 1 cm3 of the cyclohexene
in a test tube and (in the fume hood !!) carefully add a few drops of Conc. Sulphuric
acid stopper and max (with care !).
Observation:
…………………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………….
Test #3:
Put a few drops of the cyclohexene into another test tube and carefully add a few
drops of the potassium manganate(VII) solution solution.
Observation:
…………………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………….
Test #4:
Put a few drops of the cyclohexene into another test tube and carefully add a few
drops of the bromine solution.
Observation:
…………………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………….
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
Questions / Practical Summary:
Test 1 - Combustion
We know that this is a rapid free radical reaction of both the alkanes and the alkenes. However, the
alkene produced a smokier flame. The smoke is due to the presence of which element in the flame?
………………………………………………………………………………………………………………………………………………………………………………….
This is due to incomplete combustion of the hydrocarbon. Why do you think there is more of this
element in the alkene flame?
………………………………………………………………………………………………………………………………………………………………………………….
Test 2 - Sulphuric acid reaction
What is the attacking species of sulphuric acid?
…………………………………………………………….
Why does this attack the alkene and not an alkane?
………………………………………………………………………………………………………………………………………………………………………………….
Test 3 - Potassium manganate(VII) solution.
This is a powerful oxidising agent. What is the definition of an oxidising agent in terms of electrons?
………………………………………………………………………………………………………………………………………………………………………………….
Which part of the alkene molecule is attacked by the oxidising agent and why?
………………………………………………………………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………………………………………………………………….
Test 4 - Bromine solution
In this reaction, bromine adds to the molecule of ethene. How is it able to do this?
………………………………………………………………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………………………………………………………………….
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
Module Exam Questions
1.
(a)
The diagram below represents the industrial fractional distillation of crude oil.
gases
gasoline (petrol)
naphtha
A
gas oil (diesel)
mineral (lubricating) oil
crude oil
heater
residue
(i)
Identify fraction A.
...........................................................................................................................
(ii)
What property of the fractions allows them to be separated in the column?
...........................................................................................................................
(2)
(b)
A gas oil fraction from the distillation of crude oil contains hydrocarbons in the C15 to
C19 range. These hydrocarbons can be cracked by strong heating.
(i)
Write the molecular formula for the alkane with 19 carbon atoms.
...........................................................................................................................
(ii)
Name the type of reaction involved in cracking.
...........................................................................................................................
(iii)
Write an equation for one possible cracking reaction of the alkane C16H34 when
the products include ethene and propene in the molar ratio 2:1 and only one other
compound.
...........................................................................................................................
...........................................................................................................................
(4)
(Total 6 marks)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
2.
(a)
(i)
Name the alkene CH3CH2CH=CH2
...........................................................................................................................
(ii)
Explain why CH3CH2CH=CH2 does not show geometrical isomerism.
...........................................................................................................................
...........................................................................................................................
(iii)
Draw an isomer of CH3CH2CH=CH2 which does show geometrical isomerism.
(iv)
Draw another isomer of CH3CH2CH=CH2 which does not show geometrical
isomerism.
(4)
(b)
(i)
Name the type of mechanism for the reaction shown by alkenes with
concentrated sulphuric acid.
...........................................................................................................................
(ii)
Write a mechanism showing the formation of the major product in the reaction of
concentrated sulphuric acid with CH3CH2CH=CH2.
(iii)
Explain why this compound rather than one of its isomers is the major product.
...........................................................................................................................
...........................................................................................................................
(6)
(Total 10 marks)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
3.
(a)
A compound of carbon, hydrogen and nitrogen contains 61.0% of carbon and 15.3% of
hydrogen by mass.
(i)
Calculate the empirical formula of the compound.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(ii)
What other piece of data is required to deduce the molecular formula from the
empirical formula?
...........................................................................................................................
(iii)
If the molecular formula of the compound is the same as the empirical formula,
draw two possible structures of the compound.
(6)
(b)
Another compound containing only carbon, hydrogen and nitrogen can be hydrolysed
to form butanoic acid.
(i)
Draw the structure of this compound.
(ii)
Write an equation for the formation of this compound from 1-bromopropane.
...........................................................................................................................
(iii)
Give the conditions for the reaction in part (b)(ii).
...........................................................................................................................
(3)
(Total 9 marks)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
4.
(a)
The mechanism of the reaction between methane and chlorine includes the following
steps.
Step A
•CH3
+ Cl2 → CH3Cl + Cl•
Step B
•CH3
+ Cl• → CH3Cl
(i)
(ii)
Name each type of step in the mechanism.
Step A
............................................................................................................
Step B
............................................................................................................
Suggest why step A occurs more frequently than step B.
...........................................................................................................................
...........................................................................................................................
(iii)
Write an equation for the step in the mechanism which involves a methane
molecule.
...........................................................................................................................
(iv)
Deduce the structures of the two possible radicals formed initially when a
propane molecule reacts with a chlorine radical.
Radical 1
Radical 2
.................................................
.................................................
(6)
(b)
When an excess of chlorine is used in the reaction with methane, a mixture of products
is obtained, including one which contains just over 10% carbon by mass. Deduce the
molecular formula of this compound and write an overall equation for its formation
from methane.
Calculation..................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
Equation......................................................................................................................
(3)
(Total 9 marks)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
5.
(a)
Classify the following reaction.
C3H7Br + KOH → C3H6 + KBr + H2O
...............................................................................................................................
(1)
(b)
How do the physical properties of the alkene homologous series change as the chain
length increases?
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(c)
For the reaction shown in the equation:
nC 2 H 4
(i)
H
H
C
C
H
H
n
give the name of this process:
...........................................................................................................................
(2)
(d)
Most ethanol used in the chemical industry is manufactured by reacting together water
and ethene.
(i)
Write a balanced equation for this reaction.
...........................................................................................................................
(1)
(ii)
Outline the reaction conditions for this reaction.
...........................................................................................................................
...........................................................................................................................
(3)
(iii)
Classify this reaction, indicating the type of initial attack on the ethene.
...........................................................................................................................
(2)
(Total 11 marks)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
6.
(a)
Write an equation for the formation of epoxyethane from ethene and explain why the
product is highly reactive.
Equation
Explanation. ...............................................................................................................
.....................................................................................................................................
(4)
(b)
(i)
Show by an equation how one mole of epoxyethane reacts with one mole of
water and give a use for the product formed.
Equation
Use ....................................................................................................................
(ii)
Epoxyethane also reacts with ammonia. Suggest a structure for the compound
obtained when one mole of epoxyethane reacts with one mole of ammonia.
(3)
(Total 7 marks)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
7.
(a)
The reaction of chloromethane with chlorine to form trichloromethane is a free radical
substitution involving several propagation steps.
(i)
Write an overall equation for this reaction.
............................................................................................................................
(ii)
What is meant by the term propagation step?
............................................................................................................................
............................................................................................................................
(iii)
Write an equation for a propagation step in which chloromethane reacts.
............................................................................................................................
(iv)
Write an equation for a propagation step in which trichloromethane is formed.
............................................................................................................................
(4)
(b)
Write an equation and outline a mechanism for the reaction of chloromethane with an
excess of ammonia.
Equation .....................................................................................................................
Mechanism
(5)
(Total 9 marks)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
8.
The polymer poly(chloroethene), commonly known as poly(vinyl chloride) or PVC, can be
produced as follows:
H2C
CH 2
Cl 2
H
H
C
C
H
Cl
heat
C 2 H 4 Cl 2
C 2 H 3 Cl
Step 1
Step 2
Step 3
n
PVC
(a)
Using your knowledge of the reaction between bromine and ethene, name and outline a
mechanism for Step 1.
Name of mechanism ..................................................................................................
Mechanism
(5)
(Total 5 marks)
9.
(a)
There are eight structural isomers with the molecular formula C5H11Br. Four of these
are classed as primary, three as secondary and one as tertiary. The graphical formula of
one of the secondary compounds, isomer A, is shown below.
H
H
CH 3 H
H
C
C
C
C
H
H
Br
H
H
isomer A
(i)
Give the name of isomer A.
...........................................................................................................................
(2)
(ii)
Explain what is meant by the term structural isomers.
...........................................................................................................................
...........................................................................................................................
(2)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
(iii)
Draw the graphical formula of the tertiary compound with molecular formula
C5H11Br, isomer B.
isomer B
(1)
(b)
Bromoalkanes react with sodium hydroxide. More than one type of organic product can
be formed, and the relative amounts of products depend on the conditions used during
the reaction.
(i)
Write the formula of the species in aqueous sodium hydroxide that attacks the
bromoalkanes and state whether it acts as an electrophile or as a nucleophile.
Formula ............................................................................................................
Method of action ...............................................................................................
(2)
(ii)
Isomer B can react with sodium hydroxide to form a hydrocarbon if the
conditions are altered. State one change which could be made to the solvent and
one change which could be made to the temperature that would make the
hydrocarbon the major product.
Change to the solvent .......................................................................................
Change to the temperature ................................................................................
(2)
(iv)
Give the molecular formula of the hydrocarbon formed in (b)(iii), and the name
of the homologous series to which it belongs.
Molecular formula ............................................................................................
Name of homologous series .............................................................................
(2)
(Total 11 marks)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
10.
(a)
(i)
Write an equation for the formation of epoxyethane from ethene, showing the
structure of the product.
(ii)
Explain why the epoxyethane molecule is highly reactive.
......................................................................................................................
(iii)
Give the structure of the product formed by the reaction of one molecule of
epoxyethane with one molecule of water. Give one use for this product.
Structure
Use ..............................................................................................................
(5)
(b)
But-2-ene can exist in two isomeric forms. Give the structures of these two isomers and
name the type of isomerism.
Structure 1
Structure 2
Type of isomerism ................................................................................................
(3)
(Total 8 marks)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
11.
(a)
Compound A (Mr = 215.8) contains 22.24% carbon, 3.71% hydrogen and 74.05%
bromine by mass. Show that the molecular formula of A is C4H8Br2.
(3)
(b)
There are nine structural isomers of molecular formula C4H8Br2, three of which have
branched carbon chains. Give the names and draw the graphical formulae for any two
of the branched chain isomers of C4H8Br2.
Name of isomer 1 .......................................................................................................
Graphical formula of isomer 1
Name of isomer 2 .......................................................................................................
Graphical formula of isomer 2
(4)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
(c)
2-bromopropane, CH3CH(Br)CH3, will react with KOH to form two different
products.
One product is formed by an elimination reaction, while the other is formed by a
substitution reaction. For each type of reaction, suggest the condition(s) most likely to
lead to that type of reaction and draw the structure of the organic product.
(i)
Elimination reaction
Condition(s) .....................................................................................................
Structure of the product
(2)
(ii)
Substitution reaction
Condition(s) .....................................................................................................
Structure of the product
(2)
(d)
For the reaction between 2-bromopropane and potassium cyanide:
(i)
give the name or formula of the attacking species involved;
...........................................................................................................................
(1)
(ii)
give the name of the mechanism involved;
...........................................................................................................................
(1)
(iii)
write an equation for the reaction;
...........................................................................................................................
(1)
(iv)
draw the graphical structure of the organic product.
(1)
(Total 15 marks)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
12.
(a)
Classify the following reaction.
C3H7Br + KOH → C3H6 + KBr + H2O
...............................................................................................................................
(1)
(b)
How do the physical properties of the alkene homologous series change as the chain
length increases?
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(c)
For the reaction shown in the equation:
nC 2 H 4
(i)
H
H
C
C
H
H
n
give the name of this process:
...........................................................................................................................
(2)
(d)
Most ethanol used in the chemical industry is manufactured by reacting together water
and ethene.
(i)
Write a balanced equation for this reaction.
...........................................................................................................................
(1)
(ii)
Outline the reaction conditions for this reaction.
...........................................................................................................................
...........................................................................................................................
(3)
(iii)
Classify this reaction, indicating the type of initial attack on the ethene.
...........................................................................................................................
(2)
(Total 11 marks)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
13.
(a)
Write an equation for the formation of epoxyethane from ethene and explain why the
product is highly reactive.
Equation
Explanation. ...............................................................................................................
.....................................................................................................................................
(4)
(b)
(i)
Show by an equation how one mole of epoxyethane reacts with one mole of
water and give a use for the product formed.
Equation
Use ....................................................................................................................
(ii)
Epoxyethane also reacts with ammonia. Suggest a structure for the compound
obtained when one mole of epoxyethane reacts with one mole of ammonia.
(3)
(Total 7 marks)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
14.
(a)
Ethanol can be manufactured by the direct hydration of ethene and by the fermentation
of sugars.
(i)
State what is meant by the term hydration.
......................................................................................................................
(ii)
Give one advantage and one disadvantage of manufacturing ethanol by
fermentation rather than by hydration.
Do not include energy consumption or cost.
Advantage ....................................................................................................
......................................................................................................................
Disadvantage ...............................................................................................
......................................................................................................................
(3)
(b)
Ethanol can be oxidised to an aldehyde and to a carboxylic acid.
(i)
Draw the structure of this aldehyde and of this carboxylic acid.
Structure of aldehyde
(ii)
Structure of carboxylic acid
Give a suitable reagent and reaction conditions for the oxidation of ethanol to
form the carboxylic acid as the major product.
Reagent .........................................................................................................
Conditions ....................................................................................................
......................................................................................................................
(5)
j:\courses\as and a2\module #3 - introduction to organic chemistry - practical\module book\2006 module #3 - appendices.doc
(c)
(i)
Draw the structure of an alcohol containing four carbon atoms which is resistant
to oxidation.
(ii)
Draw the structure of an alcohol containing four carbon atoms which can be
oxidised to a ketone.
(2)
(d)
In the presence of a catalyst, ethanol can be dehydrated to ethene.
(i)
Give a suitable catalyst for use in this reaction.
......................................................................................................................
(ii)
Complete the mechanism for this dehydration reaction.
H
H
H
C
C
HO:
H
H
H+
(5)
(Total 15 marks)
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