Download CAPE CHEMISTRY UNIT II MODULE I Alkanes and Alkenes

CAPE CHEMISTRY UNIT II MODULE I
Alkanes and Alkenes Worksheet and Revision guide
A bit more on optical isomers [Cliff Notes – Science]
http://www.cliffsnotes.com/WileyCDA/CliffsReviewTopic/StereochemistryDefined.topicArticleId-22667,articleId-22643.html
http://www.cliffsnotes.com/WileyCDA/CliffsReviewTopic/Optical-Activity.topicArticleId22667,articleId-22644.html
http://www.cliffsnotes.com/WileyCDA/CliffsReviewTopic/Chirality.topicArticleId22667,articleId-22645.html
http://www.cliffsnotes.com/WileyCDA/CliffsReviewTopic/Projections.topicArticleId22667,articleId-22646.html
http://www.cliffsnotes.com/WileyCDA/CliffsReviewTopic/Enantiomers-andDiastereomers.topicArticleId-22667,articleId-22647.html
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Visit chemguide
Visit ausetute
Advanced Chemistry by Clugston and Flemming – Read pages 400 to 403, 408 to 413.
*** = homework – Due Friday.
ALKANES
5. Alkane – define
6. *** Combustion of alkanes – write full, balanced chemical equation with state symbols for the
combustion of the following alkanes:
 Methane, ethane, propane, pentane, octane and an alkane with 32 carbons.
7. Combustion of methane – state the following:
 Exothermic or endothermic
 Carbon to hydrogen bond strength
 Enthalpy of combustion
 Oxygen to oxygen double bond strength
 Carbon to oxygen double bond strength
 Hydrogen to oxygen bond strength
8. Explain why methane and the other alkanes will burn even though they are stable molecules.
Read Advanced Chemistry by Clugston and Flemming page 385
http://wwwchem.uwimona.edu.jm/courses/IC10Kstability.html
9. Activation energy for the combustion of cooking gas – how is it provided?
10. Why is smoking not allowed in gas stations?
11. Cracking of alkanes – thermal and catalytic cracking - define (Advanced Chemistry page 400 to
401 and chemguide)
http://www.chemguide.co.uk/organicprops/alkanes/cracking.html
12. Draw displayed formulae to illustrate cracking of decane to produce ethene and one other
molecule.
13. Write a full balanced chemical equation for (11) above. Include state symbols.
14. Comment on the reaction conditions that are required to crack alkanes
15. What is the meaning of the term ‘reaction mechanism’?
http://www.sparknotes.com/chemistry/kinetics/mechanisms/terms.html
16. Bond fission – define.
http://www.avogadro.co.uk/light/fission/bondfission.htm
CAMPION
J. MARSHALL
CAPE CHEM
U1 M1
ORGANIC – ALKANES AND ALKENES
PAGE 1 OF 5
17. Homolytic bond fission – define
18. Heterolytic bond fission – define
19. Free radical – define
http://www.avogadro.co.uk/light/fission/bondfission.htm
20. Substitution reaction
http://en.wikipedia.org/wiki/Substitution_reaction
21. Halogenation of alkanes – define
22. *** Mechanism for the free radical substitution of methane using chlorine.
http://www.avogadro.co.uk/light/fission/bondfission.htm
Draw diagrams and / or write equation to show:
 Bond fission in chlorine molecule – show movement of the bonding electrons
 Reaction between a chlorine free radical and a methane molecule – show movement of the
unpaired electron on chlorine
 Reaction between a methyl radical and a chlorine molecule - show movement of the
unpaired electron on the methyl free radical.
 Continue process to show the formation of: Monochloromethane, Dichloromethne,
Trichloromethane and Tetrachloromethane.
 The reaction between two chlorine radicals
 The reaction between two methyl radicals
23. *** For the free radical substitution of methane with chlorine identify:
 Chain INITIATION
 Chain PROPAGATION
 Chain TERMINATION
24. *** What is the function of UV radiation in the process in (21) above?
25. A campion student decided to use a mixture of bleach and an all purpose cleanser to clean the 6th
form bathrooms. Ten minutes later his eyes burned and his respiratory tract felt irritated. Give a
possible explanation.
ALKENES
26. Electrophile – define
27. Nucleophile - define
28. Electrophilic addition reaction - define
29. Write the formula of liquid bromine.
30. Mechanism for the electrophilic addition of bromine to but-2-ene
 Draw the structure of but-2-ene.
 Draw the structure of liquid bromine.
 Identify the area of high electron density
 Draw a diagram to illustrate an instantaneous or an induced dipole in a bromine molecule.
 Identify the electrophile.
 Draw an arrow to show the movement of an electron from the electron density to the
electrophile AND the movement of the electrons in bromine’s covalent bond.
 Draw a diagram of the resulting carbocation AND the bromide anion.
 Identify the nucleophile.
 Draw a diagram to show the movement of electrons from the nucleophile to the
carbocation.
 Draw the structure and write the name of the final product.
31. How would the mechanism in (30) above differ if the reaction was done with aqueous bromine
(bromine water)? HINT: WHAT ARE THE POSSIBLE THE NUCLEOPHILES.
32. State Markovnikov’s rule.
CAMPION
J. MARSHALL
CAPE CHEM
U1 M1
ORGANIC – ALKANES AND ALKENES
PAGE 2 OF 5
33. Draw the structure of an alkene that is symmetrical about its double bond.
34. Draw the structure of an alkene that is NOT symmetrical about its double bond.
35. How would the mechanism in (30) above differ if the reaction was done with hydrogen bromide
(aqueous hydrobromic acid? HINT: POLAR / IONIC CHARACTERISTICS OF HBr.
36. *** During the addition of HBr to propene the product is predominantly 2-Bromopropane. Very
little 1-Bromopropane forms. Give detailed explanation.
37. Potassium manganate (VII): hot acidified, cold acidified, alkaline – oxidizing strength
GO TO CHEMGUIDE and A-Level Chemistry by Ramsden 4th edition page 515 to 516
38. Reaction between pent-1-ene and COLD acidified potassium manganate(VII) - OXIDATION
 Write simple equation to show products formed. Use [O] to represent KMnO4.
 Draw diagram of the dialcohol.
If the potassium manganate(VII) solution is acidified with dilute sulphuric acid, the purple
solution becomes colourless. The manganate(VII) ions are reduced to manganese(II) ions.
39. Reaction between pent-1-ene and alkaline potassium manganate(VII) – OXIDATION
[Or neutral potassium manganate (VII)]
 Write simple equation to show products formed. Use [O] to represent KMnO4 or put
KMnO4 and OH- above the arrow.
Potassium manganate (VII) in alkaline solution is a weak oxidizing agent. When a gaseous alkene
is bubbled into alkaline potassium manganate(VII) solution, the purple colour fades as the alkene
is oxidized to the dialcohol. A brown suspension of manganese (IV) oxide, MnO2, appears.
Under alkaline conditions, the manganate(VII) ions are first reduced to green manganate(VI) ions .
..
. . . and then further to dark brown solid manganese(IV) oxide (manganese dioxide).
The disappearance of the purple colour of ice-cold, dilute alkaline manganate (VII) solution is a
test for a carbon-carbon multiple bond as few organic compounds are oxidized by this weak
oxidizing agent.
40. Reaction between pent-1-ene and HOT acidified potassium manganate(VII) – OXIDATION
 Oxidation to dialcohol (1o or 2o or 3o).
 Bond cleavage
 Further oxidation to two aldehydes
 Further oxidation to two carboxylic acids
 Further oxidation of methanoic acid to carbon dioxide
 What information does the formation of carbon dioxide provide about the position of the
double bond in the alkene
CAMPION
J. MARSHALL
CAPE CHEM
U1 M1
ORGANIC – ALKANES AND ALKENES
PAGE 3 OF 5
41. Reaction between pent- 2-ene and HOT acidified potassium manganate(VII) – OXIDATION
 Oxidation to dialcohol (1o or 2o or 3o).
 Bond cleavage
 Further oxidation to two aldehydes
 Further oxidation to two carboxylic acids
 What information does the formation of two carboxylic acids provide about the position of
the double bond in the alkene?
42. Reaction between 2-Methylpent- 2-ene and HOT acidified potassium manganate(VII) –
OXIDATION
 Oxidation to dialcohol (1o or 2o or 3o).
 Bond cleavage
 Further oxidation to aldehyde and ketone
 Further oxidation of aldehyde to carboxylic acid
 What information does the formation of one ketone and one carboxylic acid provide about
the structure of the alkene?
43. Reaction between ethane and concentrated sulphuric acid.
Advanced Chemistry by Clugston and Flemming – Read pages 450 to 451
A-Level Chemistry byRamsden – page 515 and 574 to 575
NOTE:
The addition of sulphuric acid across a double bond is similar to that of a hydrogen halide.
Markovnikov’s rule is followed. When ethene is bubbled into concentrated sulphuric acid
at room temperature, ethyl hydrogensulphate is formed:
Ethene (g) + cold sulphuric acid (l) 

ethyl hydrogensulphate
Draw ethyl hydrogensulphate
The product, ethyl hydrogensulphate, when added to water and warmed, is hydrolysed to
ethanol.
ethyl hydrogensulphate + warm water  ethanol + sulphuric acid

Write the overall equation
The net result is the addition of H - OH across the double bond. The industrial method of
accomplishing this is the catalytic hydration of ethene. Ethene and steam are passed at
300oC and 60 atm over phosphoric acid absorbed on silica pellets.
ALSO:
(You’ll need this when you do alcohols)
A primary alcohol reacts with cold concentrated sulphuric acid to form alkyl
hydrogensulphate :
Ethanol + conc. sulphuric acid  Ethyl hydrogensulphate + Water
If the alcohol is in excess and the reaction mixture is warmed to 140oC, an ether is formed
ethyl hydrogensulphate + ethanol (excess)  Diethyl ether (ethoxyethane) + sulphuric acid
If the concentrated sulphuric is in excess and the temperature is raised to 170oC, water is
eliminated, with the formation of an alkene:
ethyl hydrogensulphate + conc. sulphuric acid (excess)  ethene + sulphuric acid
44. Hydrogenation of fats.
http://www.chemguide.co.uk/organicprops/alkenes/hydrogenation.html
Saturated fats / lipids from animal source
No carbon to carbon double bond – unreactive – easily stored in the body
CAMPION
J. MARSHALL
CAPE CHEM
U1 M1
ORGANIC – ALKANES AND ALKENES
PAGE 4 OF 5
Saturated fats / lipids from plant source
At least one carbon to carbon double bond – more reactive – less likely to be stored in the body
Polyunsaturated – more than one carbon to carbon double bond.
Hydrogenation of plant oils changes them into soft, low melting point solids which have better
spreading propertied than butter.
Trans fat
Trans fat is the common name for a type of unsaturated fat with trans- isomer fatty acid(s). Trans fats may be
monounsaturated or polyunsaturated.
CAMPION
J. MARSHALL
CAPE CHEM
U1 M1
ORGANIC – ALKANES AND ALKENES
PAGE 5 OF 5