Form 5 Chemistry Notes Chapter 2 Carbon Compounds

1. 여철우-화학|1
FORM 5 CHEMISTRY
CHAPTER 2 CARBON COMPOUNDS
2.1 Carbon Compounds
 CARBON COMPOUNDS: Compounds that contain the element carbon.
 Organic compounds – Carbon is bonded to other elements by covalent bonds.
 Inorganic compounds – Most do not contain carbon.
Hydrocarbons
 HYDROCARBONS: Organic compounds that contain elements carbon and hydrogen on.
 Single covalent bond: Saturated hydrocarbons (Ethane, Propane)
 Double bond / Triple bond: Unsaturated hydrocarbon (Ethene, Propene)
 Main sources of hydrocarbon:
- Petroleum
- Natural gas
- Coal
 Fractions of hydrocarbons are separated by fractional distillation
- Separated based on difference in boiling points
- Lower boiling points  Distilled off earlier
 Hydrocarbons only contain carbon and hydrogen. When they are burnt in excess oxygen
(complete combustion), carbon dioxide and water are produced.
 Incomplete combustion of hydrocarbon will produce water, carbon dioxide, carbon monoxide and
carbon (as soot).
INORGANIC COMPOUNDS
CARBON COMPOUNDS
ORGANIC COMPOUNDS
Example:
 Hydrogen carbonates
 Carbonates
 Carbides
 Oxides of carbon
 Cyanides
Example:
 Hydrocarbons
 Alcohols
 Carboxylic acids
 Esters
 Carbohydrates

2. 2|여철우-화학
2.2 Alkanes
 ALKANES: Saturated hydrocarbons with general formula CnH2n+2, where n = 1, 2, 3…
 In naming alkanes according to IUPAC system, all members of alkane series have their names
ending with -ane. (IUPAC: International Union of Pure and Applied Chemistry)
 First part (prefix) of name of an alkane depends on number of carbon atoms in molecule.
Number of carbon
atoms per molecule
Prefix Name of alkane Molecular formula
1 Meth Methane CH4
2 Eth Ethane C2H6
3 Prop Propane C3H8
4 But Butane C4H10
5 Pent Pentane C5H12
6 Hex Hexane C6H14
7 Hept Heptane C7H16
8 Oct Octane C8H18
9 Non Nonane C9H20
10 Dec Decane C10H22
 Structural formula of organic compound is chemical formula that shows arrangement of atoms and
covalent bonds between atoms in molecule.
 When writing structural formula
- Each carbon atom should have four single covalent bonds
- Each hydrogen atom should have one single covalent bond
- Carbon atoms are connected by single bonds

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Physical Properties of Alkanes
 Melting and boiling points
- Low melting and boiling points because of weak Van der Waals forces between molecules.
Little energy is required to overcome the weak forces of attractions.
- When the number of carbon atoms per molecule of alkane increases, RMM increases and
melting and boiling point increases. The larger the molecular size, the stronger the Van der
Waals forces of attraction between molecules.
 Physical states
- First 4 members are gases as their boiling points are below room temperature. Alkanes from
C5 to C18 are liquids and the rest are solids.
 Density
- Less dense than water
- Increases gradually down the series as RMM increases
 Solubility
- All are insoluble in water. When liquid alkane is shaken with water, two separate layers of
liquids are formed.
- Soluble in organic solvents (E.g.: Propanone)
 Electrical conductivity
- All do not conduct electricity because they are covalent compounds consisting of molecules.
Chemical Properties of Alkanes
 Reactivity
- Less reactive compared to alkene.
 Combustion
- Undergo complete combustion in presence of excess air or oxygen to produce carbon dioxide
and water
 CH4 + O2  CO2 + 2H2O
 2C2H6 + 7O2  4CO2 + 6H2O
- Combustion is highly exothermic, produce a lot of head energy (Used as fuels)
- Incomplete combustion produces carbon (black smoke), carbon dioxide and water.
- The larger the molecular size
 the smokier (sootier) the flame
 the more heat produced on complete combustion
 Substitution reactions
- When mixture of alkane and chlorine is exposed to sunlight or UV light, substitution reaction
occurs slowly.
 Mixture of organic compounds and hydrogen chloride is produced.
- Hydrogen atoms are replaced gradually by chlorine atoms
 CH4 + Cl2  CH3Cl + HCl
 CH3Cl + Cl2  CH2Cl2 + HCl
 CH2Cl2 + Cl2  CHCl3 + HCl
 CHCl3 + Cl2  CCl4 + HCl

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The Effects of Methane on Everyday Life
 Commonly known as natural gas (Used as fuel)
 Produced by anaerobic decay of plants and organic matter
 Methane is a greenhouse as (Trap radiation energy from sun and contribute to global warming)
2.3 Alkenes
 AKLENE: Hydrocarbons with general formula CnH2n, where n = 2, 3, 4…
 Functional group in alkenes is carbon-carbon double bond (C=C)
 In naming of alkenes according to IUPAC system, all members of alkene series have their names
ending with -ene.
 Methene does not exist. (There must be minimum of two carbon atoms to from C=C).
 When writing structural formula
- There is a C=C in the chain
- Each carbon atom forms four bonds (Four single bonds/ One double bond + two single bonds)
- Each hydrogen atom should have one single covalent bond.
Number of carbon
atoms per molecule
Prefix Name of alkane Molecular formula
2 Eth Ethene C2H4
3 Prop Propene C3H6
4 But Butene C4H8
5 Pent Pentene C5H10
6 Hex Hexene C6H12
7 Hept Heptene C7H14
8 Oct Octene C8H16
9 Non Nonene C9H18
10 Dec Decene C10H20

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Physical Properties of Alkenes (Similar to Alkanes)
 Melting and boiling points
- Increase down the homologous series
 Density
- Less dese than water
 Solubility
- All are insoluble in water and soluble in organic solvents
 Electrical conductivity
- Do not conduct electricity
Chemical Properties of Alkanes
 Combustion
- Burns in excess air / oxygen to form carbon dioxide and water. Heart energy is released
during combustion
 2C3H6 + 9O2  6CO2 + 6H2O
- More luminous and smokier than alkane with same number of carbon atoms (Percentage by
mass of carbon in alkene s higher than that of alkane)
 Percentage of mass of carbon in hexane:
= ×100% = 83.7%
 Percentage of mass of carbon in hexene:
= ×100% = 85.7%
- Incomplete combustion produces carbon (black smoke) and carbon monoxide as well as water.
 Addition reactions
- ADDITION REACTIONS: Reactions in which an unsaturated organic compound combines with
another compound to form a single new saturated compound.
- Alkene contain C=C bond which is very reactive (Alkene more reactive than alkane(
- During addition reactions, C=C bond breaks open to form two new single bonds. In this
process, unsaturated compound is converted to saturated compound.
| | | |
– C = C – + X – Y  – C – C –
| |
X Y
alkene
(unsaturated)
(saturated)

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- Hydrogenation
 Addition of hydrogen molecule across C=C bond in presence of nickel / platinum as
catalyst
C3H6 + H2 → C3H8
 Use to make margarine (solid form) from vegetable oils (liquid form)
- Halogenation
 Addition reaction between alkenes and halogens (Cl and Br)
 Bromination is sued as chemical test to distinguish alkanes from alkenes. Alkenes
decolourise brown colour of liquid bromine whereas alkanes do not.
C2H4 + Br2 → C2H4Br2
- Hydration
 Water molecule is added across C=C bond in presence of phosphoric(V) acid which acts
as catalyst at 300 °C.
 Alkene is converted to alcohol on hydration.
C2H4 + H2O → C2H5OH
- Reaction with KMnO4 solution
 When alkene reacts with KMnO4 solution purple colour is decolourised immediately and
organic compound called diol is formed.
 DIOL: Saturated alcohol with two hydroxyl groups (–OH) on adjacent carbon atoms.
 In the formation of diol, two –OH groups are added across double bond in alkane.
C2H4 + H2O + [O]  C2H4(OH)2
 Like liquid bromine, KMnO4 is used to distinguish between alkane and alkenes. Alkene
decolourises purple color but alkane does not.
- Reaction with hydrogen halides
 Alkenes react with hydrogen halides at room temperature to from haloalkanes (saturated
compounds)
 Example of hydrogen halides: Hydrogen chloride, hydrogen bromide, hydrogen iodide
C2H4 + HCl  C2H5Cl

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- Polymerisation (Form polymer)
 Ethene undergoes additional polymerisation to from polyethene.
Homologous Series
 HOMOLOGOUS SERIES: Family organic compounds with same functional group and with similar
chemical properties.
 FUNCTIONAL GROUP: Atom or group of atoms that determines the chemical properties of an
organic compound.
 All members in the same homologous series
- have same function group
- have same chemical properties
- have same general formula
- can be prepared using similar methods
- show a gradual change in their physical properties
- differ from each other by a –CH2 group
Homologous series General formula Functional group
Alkanes CnH2n+2, n = 1, 2, 3… –
Alkenes CnH2n, n = 0, 1, 2… – C = C – (Carbon-carbon double bond)
Alcohols CnH2n+1OH, n = 1, 2, 3… – O – H (Hydroxyl group)
Carboxylic acids CnH2n+1COOH, n = 0, 1, 2…
O
||
– C – O – H (Carboxyl group)
Esters
CnH2n+1COOCmH2m+1,
n = 0, 1, 2…; m = 1, 2, 3…
O
||
– C – O – (Carboxylate group)

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2.4 Isomerism
 ISOMERS: Compounds which have the same molecular formula but with different structural
formula.
 ISOMERISM: Existence of two or more compounds that have the same molecular formula but with
different structural formulae.
 Same chemical properties
 Different physical properties
 Methane, ethane and propane do not have isomers.
 Butane, C4H10 has two isomers
- Straight chain (All 4 C atoms form a straight chain)
- Branched chain (3 C atoms form a straight chain with 1 C atom forming a branch)
 All alkenes bigger than propene have isomers. Butene, C4H8 has three isomers.
- Straight chain with double bond at the end of the chain
- Straight chain with a double bond in the middle of the chain
- Branched chain

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 Naming of branched isomers of alkanes according to IUPAC system
- Find the longest continuous chain of carbon atoms (parent chain)
- Name the branched chain attached to parent chain as alkyl group
 Alkyl group are named according to number of carbon atoms present
Number of carbon atoms Formula Name
1 –CH3 Methyl
2 –C2H5 Ethyl
3 –C3H7 Propyl
- Identify the position of alkyl group that is attached to parent chain by number
 Number the carbon atom in parent chain using the lowest number
 Use hyphen to separate words from numbers
- If there are more than one similar branch, use the following prefixes:
 di for two similar branched chains
 tri for three similar branched chains
 tetra for four similar branched chains
- Name the positions of carbon atoms in parent chain containing the branches.
- If there are more than one alkyl group, list the names of alkyl groups in alphabetical order.
3-ethyl-4methylhexane
 Naming of alkenes according to IUPAC system
- Select the longest carbon chain with the C=C bond as parent alkene
- Name the parent alkene according to number of carbon atoms.
- Select the position of double bond by choosing the smallest number for the carbon atom with
C=C bond.
- Name the position of double bond with number followed by hyphen.
- Identify the alkyl group and its position in the parent chain.
2-methylbut-2-ene

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2.5 Alcohols
 ALCOHOL: Have general formula CnH2n+1OH, where n = 1, 2, 3… The CnH2n+1– group represents
the alkyl group.
 Based on IUPAC system of naming straight chain alcohols, the letter e at the end name of alkane
is replaced by suffix ol.
Alkane Alkane formula Alcohol Alcohol formula
Methane CH4 Methanol CH3OH
Ethane C2H6 Ethanol C2H5OH
Propane C3H8 Propanol C3H7OH
Butane C4H10 Butanol C4H9OH
 When writing structural formula of alcohols
- Each carbon atom should have four single covalent bonds
- Each hydrogen atom should have one single covalent bond
- Each oxygen atom has two single covalent bonds
- The carbon atoms are connected by single bonds.
 Methanol and ethanol has one structural formula each (No isomer)
Industrial Production of Alcohols
 Ethanol can be produced industrially
- Hydration of ethene
 When mixture of C=2H4 and steam is passed over catalyst, H3PO4 at 300 °C and 65tm,
ethanol is produced.
- Fermentation of sugar or starch
 When yeast is added to sugar / starch, ethanol and CO2 are produced Enzyme called
zymase breaks down glucose molecules to form ethanol and CO2.
C6H12O6  2C2H5OH + 2CO2
Physical Properties of Ethanol and Other Alcohols
 Colourless liquid and has characteristic odour.
 Volatile liquid because it has low boiling point at 78 °C.
 Very soluble in water because of presence of hydroxyl group
- Hydrocarbon part of alcohol is insoluble in water
- Alcohol with large hydrocarbon chain is insoluble in water
- Solubility of alcohols in water decreases as molecular size increases
 Neutral (pH7)
 Covalent compounds (Do not conduct electricity)

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Chemical Properties of Ethanol and Other Alcohols
 Combustion
- Complete combustion occurs to produce carbon dioxide and water
2C3H7OH + 9O2 6CO2 + 8H2O
- Gives out a lot of heat energy (Good fuel)
- Incomplete combustion occurs when oxygen is insufficient
 Produce carbon monoxide gas, carbon (black sot) and water
 Oxidation
- Produces corresponding carboxylic acid
CH3CH2CH2OH + 2[O] CH3CH2CH2COOH + H2O
- Carried out by heating alcohols with oxidising agents (KMnO4 / K2Cr2O7)
 KMnO4 – Orange to green
 K2Cr2O7 – Purple to colourless
 Dehydration
- Produces corresponding alkenes (except methanol)
- Carried out by
 Passing alcohol vapour over heated porcelain chips
 Refluxing alcohol with concentrated H2SO4
Use of Alcohol in Everyday Life
 Fuels
- When burn in air, CO2 and H2O are produced, large quantity of heat energy is released
- Ethanol is a clean fuel as it does not release toxic gases in combustion.
 Solvents
- Good solvents for organic compounds (Shellac, varnish, paint)
 Medicines
- Ethanol (Mild antiseptic)
- Propan-2-ol (rubbing alcohol to reduce fever)
 Cosmetics
- Ethanol (Nail polish)
- Propan-1,2,3-triol / Glycerol (Moisturiser)
 Source of chemicals
- Ethanol (Oxidised to make vinegar)
- Methanol (Make formalin)
 Misuse and abuse of alcohols
- ALCOHOLISM: Addiction caused by excessive drinking of alcohol for a prolonged period of
time.

12. 12|여철우-화학
2.6 Carboxylic Acids
 CARBOXYLIC ACIDS: Organic acids that have general formula CnH2n+1COOH, where n = 0, 1,
2…
 Functional group of carboxylic acids: –COOH
 Based on IUPAC system of naming, carboxylic acid is named by replacing final letter e in name of
corresponding alkane with oic acid.
Number of carbon atoms Alkane Carboxylic acid
1 Methane Methanoic acid
2 Ethane Ethanoic acid
3 Propane Propanoic acid
 While writing structural formula of carboxylic acid,
- –COOH group is always at terminal carbon atom
- Carboxyl group consists of carbon atom which forms a double bond with oxygen atom and
single covalent bond with –OH group.
Name Molecular formula Structural formula
Methanoic acid HCOOH
O
||
H – C – OH
Ethanoic acid CH3COOH
O
||
CH3 – C – OH
Propanoic acid C2H5COOH
O
||
CH3 – CH2 – C – OH
Butanoic acid C3H7COOH
O
||
CH3 – CH2 – CH2 – C – OH
Preparation of Carboxylic Acid
 Prepared by oxidation of corresponding alcohol.
 CH3COOH is prepared by oxidation of C2H5OH using oxidising agent such as KMnO4 or K2Cr2O7.
 REFLUX: Method of heating mixture of C2H5OH and oxidising agent in a flask fitted with upright
Liebig condenser.
- Prevent volatile substances from escaping into atmosphere
- Ensure reactants go to complete reaction
 In oxidation of C2H5OH by K2Cr2O7:
- colour of solution changes from orange to green
- CH3COOH produced has a vinegary smell

13. 여철우-화학|13
Physical Properties of Ethanoic Acid and Other Carboxylic Acids
 Colourless liquid at room temperature. PureCH3COOH is known as glacial CH3COOH because it
freezes to form colourless crystals which look like ice.
 Has vinegary smell
 Soluble in water
 Going down homologous series:
- Solubility in water decreases
- Boiling point increases
Chemical Properties of Ethanoic Acid
 Partial ionisation
- Only a small percentage of CH3COOH molecules ionise to form H+. Most CH3COOH remains
as molecules.
 Aqueous CH3COOH turns blue litmus paper red (Also an electrolyte)
 Reaction with bases
- Forms salts and water (Neutralisation)
- Salt formed is known as ethanoate
CH3OOH + NaOH  CH3COONa + H2O
 Reaction with metal carbonates
- Forms salts, CO2 and H2O
2CH3COOH + CaCO3  (CH3COO)2Ca + CO2 + H2O
 Reaction with reactive metals (Such as Mg, Zn)
- Forms salts and hydrogen gas
2CH3COOH + Zn  (CH3COO)2Zn + H2
 Reaction with alcohol
- Form ester and water
CH3COOH + C2H5OH  CH3COOC2H5 + H2O
Chemical Properties of Other Carboxylic Acids
 React with alkalis to form salts and water
- HCOOH + NaOH  HCOONa + H2O
 React with active metals to form salts and hydrogen gas
- 2HCOOH + Mg  (HCOO2Mg + H2
 React with metallic carbonates to form salts, carbon dioxide and water
- 2HCOOH + CaCO3  (HCOO)2Ca + CO2 + H2O
 React with alcohols to form esters and water
- HCOOH + C2H5OH  HCOOC2H5 + H2O
Uses of Carboxylic Acids in Daily Life
Carboxylic acid Use
Methanoic acid To coagulate latex
Ethanoic acid To make vinegar
Benzoic acid Used as food preservative

14. 14|여철우-화학
2.7 Esters
 General formula for ester is CnH2n+1CmH2m+1 where n = 0, 1, 2… and m = 1, 2, 3…
 Functional group of ester: Carboxylate group, –COO–
 Name of ester is derived from alcohol and carboxylic acid used to prepare it
- First part of name of ester is taken from alkyl group of alcohol
Alcohol Alkyl group
Methanol Methyl
Ethanol Ethyl
Propanol Propyl
- Second part of name comes from carboxylic acid. The ending -oic of carboxylic acid is
replaced by -oate.
Carboxylic acid Carboxylate group
Methanoic acid Methanoate
Ethanoic acid Ethanoate
Propanoic acid Propanoate
- In general, names of esters are of the form ‘alkyl carbonate’ where alkyl comes from the
alcohol used to prepare the ester.
Alcohol Carboxylic acid Name of ester
Methanol Methanoic acid Methyl methanoate
Methanol Ethanoic acid Methyl ethanoate
Ethanol Ethanoic acid Ethyl ethanoate
Ethanol Propanoic acid Ethyl propanoate
 In writing structural formula of an ester using general formula R–COO–R’, the part R–CO comes
from the carboxylic acid and the part O–R’ comes from the alcohol.
- Example: Ethyl propanoate
O
||
CH3CH2C – O – CH2CH3
 ESTERIFICATION: The reaction between an alcohol and carboxylic acid to produce ester and
water.
from propanoic acid from ethanol

15. 여철우-화학|15
 Naming an ester
- Identify the alcohol part. Alcohol part is the alkyl part bonded to oxygen atom by single
bond.
- Identify the carboxylic part. Acid part is the alkyl part bonded to carbon atom with double
bond with oxygen.
- Combine two parts to name the ester. Alcohol part is named first.
O
||
CH3CH2C – O – CH2CH3
Ethyl propanoate
 Writing the structural formula of an ester (E.g.: Butyl propanoate)
- Write the general formula of ester in the form if R–COO–R’
O
||
R – C – O – R’
- Write the structural formula of alcohol part to replace –R’ (R bonded to O by single bond)
 Alcohol is butanol with four C atoms. Hence R’ is –CH2CH2CH2CH3
O
||
R – C – O – CH2CH2CH2CH3
- Write the structural formula of acid part to replace R (R bonded to C=O)
 Carboxylic acid is propanoic acid with three C atoms. Hence RCO– is CH3CH2CO–
O
||
CH3CH2 – C – O – CH2CH2CH2CH3
- Structural formula of butyl propanoate is
O
||
CH3 – CH2 – C – O – CH2 – CH2 – CH2 – CH3
Preparation of Ethyl Ethanoate
 Small quantities of ethyl ethanoate can be prepared by heating mixture of glacial CH3COOH
with pure C2H5OH in presence of small quantity of concentrated H2SO4 in boiling tube.
 To prepare large quantity, alcohol and carboxylic acid need to be heated under reflux.
 Heating under reflux is necessary as C2H5OH is very volatile. If mixture is not heated under reflux,
C2H55OH will vaporise and escape into atmosphere before it can react with CH3COOH.
Natural Sources of Esters
 Most simple esters exist naturally in flowers and fruits.
 These volatile esters are responsible for fragrant small of flowers and fruits.
 Vegetable oils and animal fats are esters with large molecules.
 Waxes such as beeswax, wax found on leaves and candle wax are solid esters.

16. 16|여철우-화학
Uses of Esters in Daily Life
 Make perfumes, cosmetics and artificial food flavouring
 Solvents for many organic compounds
 Make synthetic polymers
 Esters in oils are used to make soaps
 Used as medicine (Aspirin)
2.8 Oils and Fats
 Oils and fats are naturally occurring esters and are found in animals and plants.
 Fats are found in animals. Oils are usually found in plants and fish.
 Fats are solids at room temperature. Oils are liquids at room temperature.
- Fats have higher melting points than oils.
 When fats and oils are hydrolysed, glycerol and long chain carboxylic acids are formed.
- HYDROLYSIS: Decomposition (Breaking up) of chemical substance by water
- Ester + Water  Carboxylic acid + Glycerol
 Carboxylic acids produced from fats are also known as fatty acids. Fatty acids usually contain 16
or 18 carbon atoms per molecule.
 GLYCEROL: Alcohol that contains three hydroxyl (–OH) groups per molecule.
 Saturated carboxylic aids do not contain C=C bonds.
 Unsaturated carboxylic acids contains C=C bonds.
- Presence of C=C bonds causes lower melting points.
The Importance of Oils and Fats for Body Processes
 Sources of energy
- Fats are high energy food (Provide energy for body)
 Sources of nutrients
- Enable human to absorb vitamin A, D, E and K
 Thermal insulation
- Layer of fat beneath the skin regulates body temperature
 Protection
- Layer of fats around the vital organs acts as protective carbon
Conversion of Unsaturated Fats to Saturated Fats
 Vegetable oils can be converted to saturated fats.
 HYDROGENATION: Chemical process in which hydrogen is added to the C=C bond.
 In manufacture of margarine from vegetable oils, hydrogenation is carried out by passing H2 gas
into palm oil at 200 °C and 4 atm in presence of Ni powder as catalyst.
 The hardness of margarine formed depends on degree of hydrogenation. Partial hydrogenation
will produce soft margarine.

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Effects of Eating Food High in Fats on Health
 High consumption can lead to obesity
 Saturated fats contain high percentage of cholesterol
 Excess intake of saturated fats increase risk of
- Hypertension
- Cardiovascular disease
- Stroke
Industrial Extraction of Palm Oil
 Two types of oil extracted from fresh palm oil fruits:
- Palm oil from flesh of fruit
- Palm kernel oil from kernel or seed
Advantage of Palm Oil as a Vegetable Oil
 Rich in Vitamins A and E
 Lower LDL and raise HDL in body
 Withstand heat and resistant to oxidation, hence suitable to be used for deep frying
 Highly competitive in price
2.9 Natural Rubber
Natural Polymers
 Natural polymers: Natural rubber, carbohydrates and proteins
 Monomer of natural rubber is isoprene, C5H8 (2-methylbuta-1,3-diene)
- Natural rubber is polyisoprene
 The monomers for carbohydrates such as sugar, starch and cellulose is glucose.
- When starch is heated with dilute acid, glucose is produced.
– (C6H10O5)n – + nH2O  nC6H12O6
 Monomers of proteins are amino acids
- Amino acids are joined together by peptide linkages. Hence proteins are polypeptides.
STERILISATION
Fruit branches are sterilised to kill
fungus and bacteria.
STRIPPING
Fruits are separated from the
branches.
DIGESTION
Fruits are heated to break down the
oil-bearing cells.
PRESSING Oil is pressed out from fruits
PURIFICATION
Mixture is filtered to separate the
oil. Oil is then dried.

18. 18|여철우-화학
Coagulation of Latex
 LATEX: Colloidal solution containing an aqueous suspension of rubber particles.
 COAGULATION: Conversion of latex to the solid form.
 Each rubber contains rubber polymers enclosed with a protein membrane with negative charge.
 Negative charge on membrane’s surface repels colloidal particles from one another, preventing
rubber polymers from combining together. Hence, latex remains in liquid form.
 Coagulation of rubber can be speeded up by addition of acids.
- Hydrogen ions from acid neutralise negative charges on membranes’ surfaces of the colloidal
particles.
- When neutral rubber particles collide, the membranes will break, releasing the rubber
polymers to form lumps. Hence the latex solidifies.
 Coagulation of latex can occur without addition of acid if latex is exposed to air for few days.
- Bacteria present in latex produces organic acids.
- Hydrogen ions rom acids produced neutralises negative charges on the rubber particles.
 Coagulation can be prevented by adding aqueous ammonia.
- Hydroxide ions neutralise acids produced by bacteria.
- Negative charges at membranes of rubber particles are maintained.
Properties of Natural Rubber and Vulcanised Rubber
 Properties of natural rubber:
- Quite elastic
- Water repellent
- Does not conduct electricity
 ELASTICITY: Ability of an object to be stretched and then returned to its original shape when the
stress is removed.
 Has few practical use because:
- Not elastic enough
- Becomes soft and sticky when heated
- Becomes brittle and crack easily when oxidised by oxygen
 When natural rubber is stretched, the coiled rubber molecule is lengthened and straightened.

19. 여철우-화학|19
 VULCANISATION: Process of hardening rubber by heating it with sulphur or sulphur compounds.
- Carried out by natural rubber with sulphur at about 140 °C, using ZnO as catalyst
- Immersing rubber in a solution of S2Cl2 in methylbenzene
 In vulcanised rubber, sulphur atoms form cross-links between long chains of rubber polymers.
Improved properties of
vulcanised rubber
Explanation
Stronger and harder
Sulphur cross-links prevent polymer chains from slipping past one
another when stretched.
More elastic
Sulphur cross-links pull the chains back to their original arrangement
when released.
More resistant to heat Presence of sulphur increases the melting point of rubber.
More resistant to oxygen
Sulphur cross-links reduce the number of double bonds in the
molecules of vulcanised rubber.
Use of Natural Rubber
 Has limited uses as it is soft, has poor heat resistance and does not wear well. It becomes soft and
sticky when heated. It also becomes hard and brittle due to oxidation.
 Natural rubber is sued for making adhesive and as crepe rubber in insulating blankets.
 Things made from vulcanised natural rubber:
- Vehicle types
- Surgical gloves
- Shoe soles
- Rubber hoses
- Rubber bands
- Rubber mattresses
- Balloons
- Conveyor belts
- Shock absorbers
Research on Natural Rubber in Malaysia
 Research and development on rubber is conducted by:
- Rubber Research Institute of Malaysia (RRIM)
- Malaysian Rubber Producer Research Association (MRPRA)
- Rubber Board of Malaysia
 Scope of research and development activities
- Finding new uses of rubber and rubber products
- Improving the quality of natural rubber
- Automating the tapping system so as to overcome labour shortage

20. 20|여철우-화학
2.10 Order in Homologous Series
 Organic compounds are grouped in families called homologous series to make study of organic
chemistry more systematic and orderly.
 Alkanes, alkenes, alcohols, carboxylic acids and esters are examples of homologous series.
 Chemical properties of members of same homologous series are the same (Same functional group)
 Physical properties of members of homologous series show regular pattern and change gradually
as number of carbon atom increases.
 While going down homologous series:
- RMM increases
- Melting and boiling point increases
- Volatility decreases
- Density increases
- Solubility increases
2.11 The Variety of Organic Materials in Nature
Uses of Various Organic Materials in Everyday Life
 ORGANIC SYNTHESIS: Preparation of specific and desired organic compounds from readily
available resources.
 Research and development towards natural organic compounds enable us to:
- Stimulate structure of natural organic compounds and make useful synthetic organic
compounds
- Extract active ingredients from traditional medicines
- Produce seeds of higher quality and more resistant towards pest
- Find new uses for agriculture products