Nota kimia carbon compoun form 5

SPM Chemistry Form 5 – Terminology and Concepts: Carbon Compounds

1. Organic compounds – carbon containing compounds with covalent bonds. 2. Inorganic compounds – non-living things and usually do not contain carbon but few carbon

containing inorganic compounds such as CO2, CaCO3 and KCN.

3. Hydrocarbons – organic compounds that contain hydrogen and carbon atom only.

4. Non-hydrocarbons – organic compounds that contain other elements (oxygen, nitrogen, iodine, phosphorus)

5. Saturated hydrocarbons – only single bonded (Carbon-Carbon) hydrocarbons.

6. Unsaturated hydrocarbons – at least one double / triple bonded (Carbon-Carbon) hydrocarbons.

7. Complete combustion – organic compounds burn completely which form CO2 and H2O.Example: C2H5OH (l) + O2 (g) –> 2CO2 (g) + 3H2O (l)

8. Incomplete combustion – organic compounds burn with limited supply of O2 which form C (soot), CO, CO2 and H2O.

Homologous Series

Homologous series – organic compounds with similar formulae and properties. It have the physical properties that change gradually as the number of carbon atoms in a molecule increases.

Carbon Compounds

General Formula Functional group

Alkane CnH2n+2 n = 1, 2, 3, … Carbon-carbon single bond- C – C -

Alkene CnH2n n = 2, 3, 4, … Carbon-carbon double bond- C = C -

Alkynes CnHn n = 2, 3, 4, … Carbon-carbon triple bond- C = C -

Arenes CnH2n-6 n = 6, 7, 8, … - C = C -delocalised / free to move around the ring

Alcohol CnH2n+1OH n = 1, 2, 3, … Hydroxyl group- OH

Carboxylic Acids

CnH2n+1COOH n = 0, 1, 2 Carboxyl group- COOH

Esters CnH2n+1COOCmH2m+1 n = 0, 1, 2, …m = 1, 2, 3, …

Carboxylate group- COO -

Sources of Hydrocarbon:

1.         Coal – from the lush vegetation that grew in warm shallow coastal swamps or dead plants slowly become rock. Mainly contains of hydrocarbon and some sulphur and nitrogen. It is used to produce: fertiliser, nylon, explosives and plastics.

2.         Natural gas – from plants and animals and trapped between the layers of impervious rocks (on top of petroleum). Mainly contains of methane gas and other gas such as propane and butane. It is used for: cooking, vehicle and generate electrical power.

3.         Petroleum – from plants and animals and trapped between the layers of impervious rocks. It is a complex mixture of alkanes, alkenes, aromatic hydrocarbons and sulphur compound. These compounds can be separated by using fractional distillation.

< 35°C – petroleum gas 35°C – 75°C – Petrol (gasoline)

75°C – 170°C – Naphtha

170°C – 230°C – Kerosene

230°C – 250°C – Diesel

250°C – 300°C – Lubricating oil

300°C – 350°C – Fuel oil

> 350°C – Bitumen

A) IUPAC ( International Union of Pure and Applied Chemistry ) – is used to name organic compound.

Organic compound is divided into three portions which is Prefix + Root + Suffix.

1. Prefix – name of the branch or side chain.General formula: CnH2n+1 –Where n = 1, 2, 3, … (n = number of carbon)

Formula Branch or name  of group

CH3 - methyl

C2H5 - ethyl

C3H7 - propyl

C4H9 - butyl

C5H11 - pentyl

2. Alkyl group signifies that it is not part of the main chain.

3. Two or more types of branches are present, name them in alphabetical order.

Number of side chain Prefix

2 Di-

3 Tri-

4 Tetra-

5 Penta-

6 Hexa-

4. More than one side chains are present, prefixes are used.

5. Root – the parent hydrocarbon (denotes the longest carbon chain).

Number of carbon atoms Root name

1 meth-

2 eth-

3 prop-

4 but-

5 pent-

6 hex-

7 hept-

8 oct-

9 nan-

10 dec-

o The longest continuous (straight chain) carbon chain is selected.

o Identify the number of carbon.

6. Suffix – functional group.

Homologous series Functional group Suffix

Alkane - C – C - -ane

Alkene - C = C - -ene

Alcohol – OH -ol

Carboxylic acid – COOH -oic

Ester – COO – -oate

7. Example: 4-methylhept-2-ene.

8. Prefix + Root + Suffix

B) Family of Hydrocarbon – Alkane

1. General formula: CnH2n+2

Where n = 1, 2, 3, … (n = number of carbon)

2. Each carbon atom in alkanes is bonded to four other atoms by single covalent bonds.Alkanes are saturated hydrocarbon.

Name of alkane Molecular formula of alkane

Methane CH4

Ethane C2H6

Propane C3H8

Butane C4H10

Pentane C5H12

Hexane C6H14

Heptane C7H16

Octane C8H18

Nonane C9H20

Decane C10H22

Molecular formula is a chemical formula that shows the actual number of atoms of each type of elementspresent in a molecule of the compound.

Example: molecular formula of butane is C4H2´4+2 = C4H10

Name Condensed structural formula of alkane

Methane CH4

Ethane CH3CH3

Propane CH3CH2CH3

Butane CH3CH2CH2CH3

Pentane CH3CH2CH2CH2CH3

Hexane CH3CH2CH2CH2CH2CH3

Heptane CH3CH2CH2CH2CH2CH2CH3

Octane CH3CH2CH2CH2CH2CH2CH2CH3

Nonane CH3CH2CH2CH2CH2CH2CH2CH2CH3

Decane CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

Structural formula is a chemical formula that shows the atoms of elements are bonded (arrangement of atoms) together in a molecule by what types of bond.

3. Physical properties of alkanes

Name Molecularformula RMM Density(g cm-3)

Physical state at 25°C

Methane CH4 16 - Gas

Ethane C2H6 30 - Gas

Propane C3H8 44 - Gas

Butane C4H10 58 - Gas

Pentane C5H12 72 0.63 Liquid

Hexane C6H14 86 0.66 Liquid

Heptane C7H16 100 0.68 Liquid

Octane C8H18 114 0.70 Liquid

Nonane C9H20 128 0.72 Liquid

Decane C10H22 142 0.73 Liquid

Alkanes with more than 17 carbon atoms are solid.

Solubility in water – all members in alkanes are insoluble in water but soluble in many organic solvent (benzene and ether).

Density of alkane – the density of water is higher than density of alkane.When going down the series, relative molecular mass of alkanes is higher due to the higher force of attraction between molecules and alkane molecules are packed closer together.

Electrical conductivity – all members in alkanes do not conduct electricity.Alkanes are covalent compounds and do not contain freely moving ions.

Boiling and melting points – all alkanes in general have low boiling points and melting points.Alkanes are held together by weak intermolecular forces.

4. Chemical properties of alkanes

Reactivity of alkanesAlkanes are less reactive (saturated hydrocarbon).Alkanes have strong carbon-carbon (C – C) bonds and carbon-hydrogen (C – H) bonds.All are single bonds which require a lot of energy to break.Alkanes do not react with chemicals such as oxidizing agents, reducing agents, acids and alkalis.

Combustion of alkanesComplete combustion of hydrocarbonsCxHy + (x + y/4) O2 –> xCO2 + y/2 H2OCH4 +        2O2 –>  CO2 +    2H2OIncomplete combustionoccurs when insufficient supply of oxygenCH4 + O2 –> C + H2O2CH4 + 3O2 –> 2CO + 4H2O

Substitution reaction of alkanes (Halogenation)Substitution reaction is one atom (or a group of atoms) in a molecule is replaced by another atom (or a group of atoms).Substitution reaction of alkanes take place in ultraviolet light.Example:Alkanes react with bromine vapour (or chlorine) in the presence of UV light.CH4 + Cl2 –> HCl + CH3Cl (Chloromethane)CH3Cl + Cl2 –> HCl + CH2Cl2 (Dichloromethane)CH2Cl2 + Cl2 –> HCl + CHCl3 (Trichloromethane)CHCl3 + Cl2 –> HCl + CCl4 (Tetrachloromethane)

The rate of reaction between bromine and alkanes is slower than the rate of reaction between chlorine and alkanes.

Family of Hydrocarbon – Alkene

1. General formula: CnH2n

Where n = 2, 3, 4 … (n = number of carbon)

2. Alkenes are unsaturated hydrocarbons which contain one or more carbon-carbon (C = C) double bonds in molecules.

3. The functional group in alkenes is carbon-carbon double (C = C) bond.

Name of alkene Molecular formula of alkene

Ethene C2H4

Propene C3H6

Butene C4H8

Pentene C5H10

Hexene C6H12

Heptene C7H14

Octene C8H16

Nonene C9H18

Decene C10H20

Molecular formula is a chemical formula that shows the actual number of atoms of each type of elements present in a molecule of the compound.Example: molecular formula of butene is C4H2x4 = C4H8

4. Physical properties of alkenes

Name Molecularformula RMM Density(g cm-3)

Physical state at 25°C

Ethene C2H4 28 0.0011 Gas

Propene C3H6 42 0.0018 Gas

Butene C4H8 56 0.0023 Gas

Pentene C5H10 70 0.6430 Liquid

Hexene C6H12 84 0.6750 Liquid

Heptene C7H14 98 0.6980 Liquid

Octene C8H16 112 0.7160 Liquid

Nonene C9H18 126 0.7310 Liquid

Decene C10H20 140 0.7430 Liquid

Solubility in water – all members in alkenes are insoluble in water but soluble in many organic solvent (benzene and ether).

Density of alkene – the density of water is higher than density of alkene.When going down the series, relative molecular mass of alkenes is higher due to the higher force of attraction between molecules and alkene molecules are packed closer together.

Electrical conductivity – all members in alkenes do not conduct electricity.Alkenes are covalent compounds and do not contain freely moving ions.

Boiling and melting points – all alkenes in general have low boiling points and melting points. Alkenes are held together by weak attractive forces between molecules (intermolecular forces) van der Waals’ force. When going down the series, more energy is required to overcome the attraction. Hence, the boiling and melting points increases.

5. Chemical properties of alkenes

Reactivity of alkenesAlkenes are more reactive (unsaturated hydrocarbon).Alkenes have carbon-carbon (C = C) double bonds which is more reactive than carbon-carbon (C-C) single bonds. All the reaction occur at the double bonds.

Combustion of alkenesComplete combustion of hydrocarbons (alkenes)CxHy + (x + y/4) O2 –> xCO2 + y/2 H2OC2H4 +        3O2 –>  2CO2 +    2H2O

(Alkenes burn with sootier flames than alkanes. It is because the percentage of carbon in alkene molecules is higher than alkane molecules and alkenes burn plenty of oxygen to produce carbon dioxide and water)

Incomplete combustion occurs when insufficient supply of oxygenC2H4 + O2 –> 2C + 2H2OC2H4 + 2O2 –> 2CO + 2H2O(The flame in the incomplete combustion of alkenes is more smoky than alkanes)

Polymerisation reaction of alkenesPolymers are substances that many monomers are bonded together in a repeating sequence.Polymerisation is small alkene molecules (monomers) are joined together to form a long chain (polymer).nCH2 = CH2 –> -(- CH2 – CH2 -)-n

ethene (monomer)(unsaturated compound) –> polyethene polymer (saturated compound)It must be carry out in high temperature and pressure.

Addition of hydrogen (Hydrogenation)Addition reaction is atoms (or a group of atoms) are added to each carbon atom of a carbon-carbon multiple bond to a single bond.C2H4 + H2 –> C2H6 (catalyst: nickel and condition: 200°C)Example: margarine (produce from hydrogenation of vegetable oils).

Addition of halogen (Halogenation)Halogenation is the addition of halogens to alkenes (no catalyst of ultraviolet light is needed).Alkene + Halogen –> DihaloalkaneC2H4 + Br2 –> C2H4Br2

In this reaction the brown colour of bromine decolourised (immediately) to produce a colourless organic liquid.Bromination is also used to identify an unsaturated (presence of a carbon-carbon double bond) organic compound in a chemical test.

Addition of hydrogen halidesHydrogen halides (HX) are hydrogen chlorine, hydrogen bromide, hydrogen iodide and etc. This reaction takes place rapidly in room temperature and without catalyst.CnH2n + HX –> CnH2n+1XC2H4 + HBr –> C2H5Br (Bromoethane)(There are two products for additional of hydrogen halide to propene. The products are 1-bromopropane and 2-bromopropane).

Addition of water (Hydration)Alkenes do not react with water under ordinary condition. It can react with a mixture of alkene and steam pass over a catalyst (Phosphoric acid, H3PO4). The product is an alcohol.CnH2n + H2O –> CnH2n+1OHC2H4 + H2O –> C2H5OH

Additional of acidified potassium manganate(VII), KMnO4

CnH2n + [O] + H2O –> CnH2n(OH)2

C2H4 + [O] + H2O –> C2H5(OH)2The purple colour of KMnO4 solution decolourised immediately to produce colourless organic liquid. Also used to identify the presence of a carbon-carbon double bond in a chemical test.

1. Comparing (Similarities and Differences) Properties of Alkanes and Alkenes

Physical Properties

Alkanes Alkenes

Physical state Physical state changes from gas to liquid when going down the series.

Same with alkanes.

Electrical conductivity.

Do not conduct electricity at any state.

Same with alkanes.

Boiling points and melting points

Low boiling points and melting points (number of carbon atoms per molecule increases).

Same with alkanes.

Density Low densities (number of carbon atom per molecule increases).

Same with alkanes.

Solubility in water

Insoluble in water (soluble in organic solvent)

Same with alkanes.

Chemical Properties

Alkanes (Substitution reaction)

Alkenes (Addition reaction)

Reactivity Unreactive Reactive

Combustion Burn in air and produce yellow sooty flame.

Burn in air and produce yellow and sootier flame compare to alkanes.

Reaction with bromine solution

No reaction. Decolourise brown bromine solution.

Reaction with acidified potassium manganate(VII) solution

No reaction. Decolourise purple acidified potassium manganate(VII) solution.

2. Isomerism Isomerism – phenomenon that two or more molecules are found to have the same

molecular formula but different structural formulae. Isomerism in alkanes

Molecular formula Number of isomers Structure name

CH4 - (no isomer) Methane

C2H6 - (no isomer) Ethane

C3H8 - (no isomer) Propane

C4H10 2 Butane2-methylpropane

C5H12 3 Pentane2-methylbutane2,2-dimethylpropane

Isomerism in alkenes

Molecular formula Number of isomers Structure name

C2H4 - (no isomer) Ethene

C3H6 - (no isomer) Propene

C4H8 3 But-1-eneBut-2-ene2-methylpropene

C5H10 5 Pent-1-enePent-2-ene2-methylbut-1-ene

3-methylbut-1-ene

2-methylbut-2-ene

Non-Hydrocarbon – Alcohol

1. General formula: CnH2n + 1OH

Where n = 1, 2, 3 … (n = number of carbon)

2. Alcohols are non-hydrocarbons which contain carbon, hydrogen and oxygen atoms. 3. The functional group in alcohols is hydroxyl group, – OH.

Name of alcohol Molecular formula of alcohol

Methanol CH3OH

Ethanol C2H5OH

Propanol / Propan-1-ol C3H7OH

Butanol / Butan-1-ol C4H9OH

Pentanol / Pentan-1-ol C5H11OH

Hexanol / Hexan-1-ol C6H13OH

Heptanol / Heptan-1-ol C7H15OH

Octanol / Octan-1-ol C8H17OH

Nonanol / Nonan-1-ol C9H19OH

Decanol / Decan-1-ol C10H21OH

4. Physical properties of alcohol

Name Molecular formula

Melting point (°C)

Boiling point (°C)

Physical state at 25°C

Methanol CH3OH -97 65 Liquid

Ethanol C2H3OH -117 78 Liquid

Propanol C3H5OH -127 97 Liquid

Butanol C4H7OH -90 118 Liquid

Pentanol C5H9OH -79 138 Liquid

Solubility in water – all members in alcohol are very soluble in water (miscible with water).

Volatility – all alcohols are highly volatile.

Colour and Smell – alcohols are colourless liquid and have sharp smell.

Boiling and melting points – all alcohols in general have low boiling points (78°C).

5. Chemical properties of alcohol

Combustion of alcohol Complete combustion of alcohol. C2H5OH + 3O2 –> 2CO2 + 3H2O (Alcohol burns with clean blue flames. Alcohol burns plenty of oxygen to produce carbon dioxide and water. This reaction releases a lot of heat. Therefore, it is a clean fuel as it does not pollute the air.) Other example: 2C3H7OH + 9O2 –> 6CO2 + 8H2O

Oxidation of ethanol In the laboratory, two common oxidising agents are used for the oxidation of ethanol which are acidified potassium dichromate(VI) solution (orange to green) and acidified potassium manganate(VII) solution (purple to colourless). C2H5OH + 2[O] –> CH3COOH + H2O Ethanol oxidised to ethanoic acid (a member of the homologous series of carboxylic acids – will be discussed in Part 6). Other example: C3H7OH + 2[O] –> C2H5COOH + H2O

Removal of water (Dehydration) Alcohol can change to alkene by removal of water molecules (dehydration). It results in the formation of a C=C double bond. CnH2n+1OH –> CnH2n + H2O C2H5OH –> C2H4 + H2O Two methods are being used to carry out a dehydration in the laboratory. a) Ethanol vapour is passed over a heated catalyst such as aluminium oxide, unglazed porcelain chips, pumice stone or porous pot. b) Ethanol is heated under reflux at 180°C with excess concentrated sulphuric acid, H2SO4. Other example: C3H7OH –> C3H6 + H2O

6. Uses of Alcohol

Alcohol as a solvent (cosmetics, toiletries, thinners, varnishes, perfumes). Alcohol as a fuel (fuel for racing car, clean fuel, alternative fuel).

Alcohol as a source of chemicals (polymer, explosives, vinegar, fiber).

Alcohol as a source of medical product (antiseptics for skin disinfection, rubbing alcohol).

7. Misuse and Abuse

Depressant drug

Alcoholic drinks

Addictive drug

Non-Hydrocarbon – Carboxylic Acids

1. General formula: CnH2n+1COOH

Where n = 0, 1, 2, 3 … (n = number of carbon)

2. Carboxylic acids are non-hydrocarbons which contain carbon, hydrogen and oxygen atoms.

3. The functional group in alcohols is carboxyl group, – COOH.

Name of carboxylic acids Molecular formula of alcohol

Methanoic acid(Formic acid) HCOOH

Ethanoic acid(Acetic acid) CH3COOH

Propanoic acid C2H5COOH

Butanoic acid C3H7COH

4. Physical properties of carboxylic acid

Name Molecularformula Boiling point (°C)

Methanoic acid(Formic acid) HCOOH 101

Ethanoic acid(Acetic acid) CH3COOH 118

Propanoic acid C2H5COOH 141

Butanoic acid C3H7COH 164

Solubility in water – generally in carboxylic acid (the less than four carbon atoms) are very soluble in water and ionise partially to form weak .

Density of carboxylic acid – density of carboxylic acid increases due to the increases in the number of carbon atoms in a molecule.

Boiling points – all carboxylic acid in general have relatively high boiling points than the corresponding alkanes. This is due to the presence of carboxyl group in carboxylic acid.

Smell – carboxylic acid (< 10 carbon) are colourless and pungent smell. Carboxylic acid (>10 carbons) are wax-like solids.

5. Preparation of carboxylic acid

Oxidation of an alcoholThe oxidation of ethanol is used to prepare ethanoic acid.C2H5OH + 2[O] –> CH3COOH + H2OCarried out by refluxing* ethanol with an oxidising agent[acidified potassium dichromate(VI) solution – orange colour turns to green /acidified potassium manganate(VII) solution – purple colour turns to colourless]* reflux = upright Liebig condense to prevent the loss of a volatile liquid by vaporisation.

6. Chemical properties of carboxylic acid

Acid propertiesEthanoic acid is a weak monoprotic acid that ionises partially in water (produce a low concentration of hydrogen ions).CH3COOH <–> CH3COO- + H+

Ethanoic acid turns moist blue litmus paper red. Reaction with metals

Ethanoic acid reacts with reactive metals (copper and metals below it in the reactivity series cannot react with ethanoic acid).(K, Na, Mg, Al, Zn, Fe, Sn, Pb, Cu, Hg, Au)2CH3COOH + Zn –> Zn(CH3COO)2 + H2

In this reaction, a colourless solution (zinc ethanoate) is formed.2CH3COOH + Mg –> Mg(CH3COO)2 + H2

In this reaction, a colourless solution (magnesium ethanoate) is formed.

Reaction with basesacid neutralises alkalis (sodium hydroxide).CH3COOH + NaOH –> CH3COONa + H2OIn this reaction, a salt (sodium ethanoate) and water are formed.

Reaction with carbonatesEthanoic acid reacts with metal carbonates (calcium carbonate, magnesium carbonate, zinc carbonate).2CH3COOH + CaCO3 –> Ca(CH3COO)2 + CO2 + H2OIn this reaction, a salt (calcium ethanoate), carbon dioxide and water are formed.

Reaction with alcohols (Esterification)Ethanoic acid reacts with alcohol (ethanol, propanol, butanol)CH3CO-OH + H-OC4H9 –> CH3COOC4H9 + H2O (Concentrated H2SO4 is a catalyst)In this reaction, an ester (colourless sweet-smelling liquid) (butyl ethanoate) and water are formed.

7. Uses of Carboxylic Acid

Carboxylic acid (methanoic acid and ethanoic acid) is used to coagulate latex. Vinegar (dilute 4% of ethanoic acid) is used as preservative and flavouring.

Ethanoic acid is used to make polyvinvyl acetate which is used to make plastics and emulsion paints.

Benzoic acid is used as food preservative.

Butanoic acid is used to produce ester (artificial flavouring).

Non-Hydrocarbon – Fats

1. Fatrs are non-hydrocarbons which contain carbon, hydrogen and oxygen atoms.

2. Fats (lipids / triglycerides) are belonging to the group in ester.

3. Natural esters are formed from glycerol and fatty acids.

Name of fat Molecular formula of ester Types of fatty acids

Lauric acid* CH3(CH2)10COOH Saturated

Palmitic acid* CH3(CH2)14COOH Saturated

Stearic acid* CH3(CH2)16COOH Saturated

Oleic oxide ** CH3(CH2)7CH=CH(CH2)7COOH Unsaturated

Linoleic acid***

CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH Unsaturated

Linolenic acid***

CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH Unsaturated

* Saturated: C-C single bonds

** Unsaturated (monounsaturated): C=C double bonds

*** Unsaturated (polyunsaturated): C=C double bonds

4. Animal fats have higher percentage of saturated fatty acids than unsaturated fatty acids.

5. Plant oils have higher percentage of unsaturated fatty acids than saturated fatty acids.

6. Physical properties of fats

Saturated Unsaturated

Types of fatty acids C-C single bonds C=C double bonds

Bonding single double

Melting point higher lower

Sources animals plants

Cholesterol high low

State at room temperature solid liquid

Fats (animal) in general are solids at room temperature and acted as:

thermal insulator protective cushion to protect the vital organ

provide energy and stored in body

carry Vitamin A, D, E, K (insoluble in water)

Example: butter, fish oil (liquid in room temperature)

Fats (plant) are called oils. Oils are liquids at room temperature.

Example: olive oil, peanut oil, palm oil and bran oil

7. Chemical properties of fats

Unsaturated fats can be converted into saturated fats by hydrogenation (additional reaction) in 200°C and 4 atm in the presence of nickel catalyst.

Example: production of margarine from sunflower oil of palm oil.

8. Effect of fats

Fatty food produce high energy but high consumption of fatty food will results:

obesity raise the level of cholesterol

deposition will cause block the flow of blood which lead to stroke and heart attack.

9. Palm oil

It is extracted from fresh oil palm fruits. Palm oil – extracted from the pulp of the fruits.

Steps in extraction of palm oil:

1. sterilising (oil palm fruit) 2. stripping

3. digestion (crushing the husk and fruit and separate the oil by heating)

4. squeezed out the oil

5. extraction (separate the oil from water)

6. purification the oil (palm oil is treated with phosphoric acid and then steam is passed through to separate the acid)

7. vacuum

Palm kernel oil – extracted from the kernel or seed.

Steps in extraction of palm oil:

1. sterilising (oil palm fruit) 2. stripping

3. crushing the husk and fruit

4. extracting kernel oil

5. purification (purify the oil from kernel)

Goodness in palm oil:

higher proportion of unsaturated fats. easy to digest and absorb.

rich in vitamin A (carotenoid)

rich in vitamin E (tocophenols and tocotrienols)

resist oxidation in high temperature.

Polymers

1. Polymer – many small units (monomers) joining together to formed large molecule.

2. Polymer can be classified into two groups:

synthetic polymers / man-made polymers (polythene; PVC – polyvinyl chloride; artificial silk; and polypropene)

natural polymers (natural rubber; starch; cellulose; and proteins)

3. Natural polymer: Carbohydrates (polysaccharides) (starch, glycogen and cellulose)

General formula: Cx(H2O)y with the ratio of H:O = 2:1 Carbohydrates have cyclic structure.

Monomer: glucose (C6H12H6)

Reaction to form polymer: condensation reaction (- H2O)

4. Natural polymer: Protein (polypeptide)

Protein consists of carbon, hydrogen, oxygen and nitrogen (some have sulphur, phosphorus and other elements)

Monomer: amino acids

Amino acids have two functional group which are carboxyl group (-COOH) and amino group (-NH2)

Reaction to form polymer: condensation reaction (- H2O)

5. Natural polymer: Natural rubber

Extracted from the latex of rubber tree (Hevea brasiliensis) which the tree originates from Brazil.

A molecule of rubber contains 5000 isoprene units.

Monomer: isoprene, C3H8 or 2-methylbuta-1,3-diene.

Reaction to form polymer: additional polymerisation (one of the double bond in isoprene becomes single bond)

6. Structure of rubber molecule

Latex is colloid (35% rubber particles and 65% water). Rubber particle contains rubber molecules which are wrapped by a layer of

negatively-charged protein membrane. Same charge of rubber molecules repels each other. This prevent rubber from coagulate.

7. Coagulation process of latex

The process for the coagulation of latex is summarised as:

1. Acid (H+) can neutralise the negatively-charged protein membrane. Example of acid: formic acid, methanoic acid, suphuric acid and hydrochloric acid.

2. The rubber molecules will collide after the protein membrane is broken.

3. Rubber molecules (polymers) are set free

4. Rubber molecules combine with one another (coagulation).

8. Natural coagulation process of latex

For the natural coagulation of latex:

1. Latex is exposed to air without adding acid (duration – overnight). 2. Coagulation process occurs in slower pace due to the bacteria (microorganism) action

which produce acid)

9. Prevent coagulation process of latex

The following are latex coagulation prevention method:

1. Alkaline / Basic solution is added to the latex. Example: ammonia (NH3). 2. Positively-charged hydrogen ion / H+ produced by bacteria can be neutralised by

negatively-charged hydroxide ion / OH- from ammonia solution.

10. Properties of natural rubber

elastic cannot withstand heat (become sticky and soft – above 50°C; decompose – above

200°C; hard and brittle – cooled)

easily oxidised (present of C=C)

insoluble in water (due to the long hydrocarbon chains)

soluble in organic solvent (propanone, benzene, petrol etc.)

11. Vulcanisation of rubber

Vulcanisation – process of hardening rubber and increases rubber elasticity by heating it with sulphur or sulphur compounds.

Methods:

heating natural rubber with sulphur at 140°C using zinc oxide as catalyst or dipping natural rubber in a solution of disulphur dichloride (S2Cl2) in methylbenzene.

12. Properties of vulcanisation of rubber

The sulphur atoms are added to double bonds in the natural rubber molecules to form disulphide linkages (-C-S-S-C-) / sulphur cross-links between the long polymer chains. Therefore, vulcanised rubber is more elastics and stronger.

This increases the molecular size and the intermolecular forces of attraction between rubber molecules. Therefore, vulcanised rubber is more resistant to heat (does not become soft and sticky when hot).

This also reduces the number of carbon-carbon double bonds in rubber molecules. Therefore, vulcanised rubber is more resistant to oxygen, ozone, sunlight and other chemicals.

13. Comparison between the properties of vulcanised rubber and unvulcanised rubber

Properties Vulcanised rubber Unvulcanised rubber

Double bonds Decreases (formation of sulphur cross-links)

More number of double bonds

Melting point High (presence of sulphur) Low

Elasticity More elastic (sulphur cross-links prevents the polymer chain or rubber from slipping past.

Less elastics

Strength and hardness

Strong and hard (depends on degree of vulcanisation)

Weak and soft (polymer chain of rubber will break when rubber is over stretched.

Resistant to heat

Resistant to heat Poor resistant to heat

Oxidation Resistant to oxidation (reduction of number of double bonds per rubber molecule)

Easily oxidised by oxygen, UV light (presence of many double bonds per rubber molecules)

14. R & D of rubber

RRIM – Rubber Research Institute of Malaysia MRB – Malaysian Rubber Board

Rubber Technology Centre

Various local higher institutions of learning