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Chapter 11 Carbon Compounds Carbon Compounds

Usually contain CARBON and HYDROGEN only or CARBON and HYDROGEN with other non-metal

elements (Oxygen, Nitrogen, Sulphur, Phosphorus and Halogens).

Can be classified into two groups : Organic Compounds + Inorganic Compounds

Organic Compounds

All carbon-containing compounds are organic compounds EXCEPT oxide of carbon and carbonate.

Eg. Nylon, Protein, Petrol, Plastic, Cellulose, Fat, Starch, Alcohol, Carboxylic Acid

Combustion :-

- Complete Combustion (EXCESS oxygen) : [Organic Compounds + O2 → CO2 + H2O]

- Incomplete Combustion (LIMITED oxygen) : [Organic Compounds + O2 → C / CO + H2O]

- More smoke is produced in the incomplete combustion than the complete combustion.

Inorganic Compounds

All non carbon-containing compounds + Few carbon-containing compounds (oxide of carbon and

carbonate)

Eg. Carbon monoxide, Potassium Cyanide, Sodium Carbonate, Aluminium Carbide.

Hydrocarbon

The most common natural sources of hydrocarbons are petroleum and natural gas.

Eg. Alkane, Alkene.

SINGLE covalent bonds / DOUBLE covalent bonds / TRIPLE covalent bonds (Carbon - Other

elements)

Can be classified into two groups :-

Saturated (only single covalent bonds) + Unsaturated (at least one double or triple covalent bond)

Non-hydrocarbon

Eg. Alcohol, Carboxylic Acd, Ester, Fat, Natural Rubber

Carbon Compounds

Organic Compounds

Hydrocarbons

Saturated Hydrocarbons

Unsaturated Hydrocarbons

Non-hydrocarbons

Inorganic Compounds

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Physical Properties Comparison Among All The Organic Compounds

Organic Compounds

Alcohol Carboxylic Acid Ester

Colour All are colourless (1 – 12) All are colourless Colourless

Physical State Number of carbon 1 – 12 : Liquid > 12 : Solid

Number of carbon 1 – 10 : Liquid > 10 : Solid

Volatile compound

Melting and Boiling Point

Higher than corresponding alkane, alkene and alcohol

Lower than corresponding alcohol and carboxylic acid.

Carboxyl group contains two types of bonds – double bond and single bond.

Increase when going down the group

Number of carbon atoms in the molecule increase. Thus, the molecular size of increases and the weak

Van der Waals’ force of attraction between the molecules become stronger.

Thus, more energy is required to overcome the strong Van der Waals’ force of attraction when going down the group.

Density

Increase when going down the group

The relative molecular mass of the molecule increase and molecules are packed more closely together.

Solubility (Water)

The hydroxyl part is soluble in water but the hydrocarbon part insoluble in water

When the effect of the hydroxyl part on solubility is greater than the effect of the hydrocarbon parts = soluble in water

(1 – 3 : soluble > 4 : insoluble

The carboxyl part is soluble in water but the hydrocarbon part insoluble in water

When the effect of the carboxyl part on solubility is greater than the effect of the hydrocarbon parts = soluble in water

(1 – 4 : soluble > 5 : insoluble

Insoluble (will form an oily layer on water)

Solubility (Organic Solvent

[Benzene])

Soluble

Electrical Conductivity

d

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Alkanes (C2H2n+2, n = 1, 2, 3 …)

Unreactive compounds because they are saturated compounds as the STRONG carbon-carbon and

carbon-hydrogen single bonds must be broken for the alkanes to react.

Neutral compounds and have no effect on red or blue litmus paper plus do not react with acid or

alkali.

Chemical Properties :-

(a) Combustion (Complete and Incomplete)

- Large quantities of heat are liberated, making it suitable to be used as a fuel.

- When the number of carbon atom per molecule increases, the alkanes produces more heat

and become less flammable - more difficult to burn [as the molecular size of the alkane

molecule increases] plus the flame becomes more smoky [as the percentage of carbon in the

alkane molecule increases].

(b) Halogenation [Exposed to ultraviolet light / sunlight]

- Carbon-hydrogen bonds are broken and new carbon-halogen bonds are formed.

- When a mixture of alkane and halogen is exposed to ultraviolet light or sunlight, a reaction in

which the hydrogen atoms in alkane are replaced step by step by halogen atoms.

- Replaced by chlorine : Chlorination

Replaced by bromine : Bromination

- Rate of reaction (ALKANE & BROMINE) slower than rate of reaction (ALKANE & CHLORINE)

Because chlorine has a higher position in electrochemical series.

- Iodine does not react with alkanes as the reaction is too slow.

Alkenes (C2H2n, n = 2, 3, 4 …)

Very reactive compounds because they are unsaturated compounds as the carbon-carbon double

bonds is very easy to be broken and react with others.

For alkene molecules containing three or more carbon atoms, the position of the double bond must

be specified.

Chemical Properties :-

(a) Combustion (Complete and Incomplete)

- The flame is smokier than the corresponding alkanes.

- The percentage by mass of carbon in alkenes is always the same, 85.71%.

(b) Hydrogenation [Nickel or platinum + 180C]

- Used in the manufacture of margarine (solid) from natural vegetable oil (liquid).

C3H6 + H2 → C3H8

Propene + Hydrogen → Propane

(c) Halogenation [No catalyst and no ultraviolet light]

- As a chemical test to identify unsaturated hydrocarbon (double bond) as saturated organic

compound do not decolourise liquid halogen but unsaturated organic compound will.

C3H6 + Br2 → C3H6Br2

Propene + Bromine → 1,2 - dibromopropane

(d) Addition of Hydrogen Halide

- To produce chloro-alkane, bromo-alkane and iodo-alkane

C3H6 + HCl → C3H7Cl

Propene + Hydrogen Chloride → Chloropropane

(e) Hydration [Phosphoric acid + 300C + 60 atm]

- Alkanes do not react with cold water under ordinary conditions.

C3H6 + H2O → C3H7OH

Propene + Water → Propan-1-ol

(f) Addition of Hydroxyl Groups [Diluted acidified potassium manganate (VII) solution]

- Diluted acidified potassium manganate (VII) solution (Mixture of potassium manganate (VII)

solution and dilute sulphuric acid – strong acid)

- Purple colour of potassium manganate (VII) solution is decolourised and a colourless organic

compound called a diol is formed.

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- As a chemical test to identify unsaturated hydrocarbon (double bond) as saturated organic

compound do not decolourise the purple solution of potassium manganate (VII) solution but

unsaturated organic compound will.

C3H6 + [O] + H2O → C3H7(OH)2

Propene + [O] + Water → Propan-1,2-diol

(g) Polymerisation [200C + 1200 atm]

H H

→

H H | | | | n C = C --- C - C ------- | | | | H | H | H - C - H H - C - H n | | H H Propene → Polypropene

Alcohol (C2H2n+1OH, n = 1, 2, 3 …)

Hydroxyl group (functional group) determines the chemical properties as it take parts in the chemical

reaction.

There is not hydroxide ions, OH- in alcohol, thus, alcohol does not show any alkali properties.

For alkene molecules containing three or more carbon atoms, the position of the double bond must

be specified.

Chemical Properties :-

(a) Combustion (Complete and Incomplete)

- Alcohols are very flammable substances and burns with a non-smoky blue flame in complete

combustion.

- Combustion of alcohol gives out a lot of heat energy, making alcohol as a good fuel.

- Alcohol is a clean fuel because it does not release pollutants into the atmosphere.

(b) Oxidation

- Oxidising agent is needed.

Acidified Potassium Manganate (VII) Solution / Acidified Potassium Dichromate (VI) Solution

C3H7OH + 2[O] → C2H5COOH + H2O

Propanol + Acidified Potassium Manganate (VII) Solution → Propanoic Acid + Water

(c) Dehydration

- Alcohol vapour is passed over a heated catalyst (Porcelain chips / Porous pot / Aluminium

Oxide)

- Alcohol is heated under reflux + 170C + Excess Concentrated Sulphuric Acid

C3H7OH → C3H6 + H2O

Propanol → Propene + Water

Uses of alcohol :-

- As a fuel – clean fuel, bio fuel, gasohol

- As a solvent – perfumes, cosmetics, toiletries

- As a thinner – lacquer, varnish, shellac, ink

- As a cleaner – compact disc, video cassette, recorder head

- As a raw material in the manufacturer of vinegar, plastics and explosives.

- As a raw material to make pharmaceutical products – tincture, antiseptic, cough syrup and rubbing

alcohol.

- In making alcoholic drinks – beers, wines, spirits

Carboxylic Acid (CnH2n+1COOH, n = 0, 1, 2 …)

Colourless liquid with vinegar smell and turns blue litmus paper to red.

Carboxyl group (functional group) determines the chemical properties as it take parts in the chemical

reaction. It consists of a carbon atom which forms a double bond with an oxygen atom and a single

bond with the hydroxyl group.

Chemical Properties :-

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Carboxylic acid is a weak monoprotic because it undergoes partial ionisation in water with low

concentration of hydrogen ions, H+. Thus, it has similar chemical properties with WEAK acid.

(a) Esterification [Concentrated Sulphuric Acid]

- This reaction is only for carboxylic acid.

- Concentrated sulphuric acid acts as catalyst to speed up the esterification reaction and also

acts as drying agent – absorbs water to produce more ester.

- Water is formed from the reaction between the HYDROGEN ions, H+ from carboxylic acid and

HYDROXIDE ions, OH- from alcohol.

C3H7OH + C2H5COOH → C2H5COOC3H7 + H2O

Propanol + Propanoic Acid → Propyl Propanoate + Water

Uses of carboxylic acid :-

- Methanoic acid – to coagulate latex

- Ethanoic acid – preservative and flavouring in food

- Benzoic acid – preservative in food (as perfumes)

Ester CnH2n+1COOCmH2m+1, n = 0, 1, 2 … and m = 1, 2, 3 …)

Colourless liquid with a sweet smell (fruits or flowers).

Uses of carboxylic acid :-

- To make perfumes, cosmetics and food flavourings.

- As a solvent for many organic compound (sunburn lotion)

- Production of soaps and detergents.

- To make synthetic polymer (polyester) which is used as synthetic fibres for making clothing fabrics.

Preparation of Alcohol

PICTURE a) Hydration in petroleum fractions (industry)

b) Fermentation between sugar and starch

Anaerobic in which means it take place in the absence of oxygen

Yeast releases biological enzyme called zymase and the zymase will slowly decompose the

glucose to form ethanol and carbon dioxide.

Preparation of Carboxylic Acid

PICTURE The flask is fitted with an upright condenser to prevent the loss of a volatile liquid by vaporisation.

(Condense alcohol vapour to liquid alcohol and then flow back to the flask)

Method of retaining a volatile liquid during heating is called refluxing and it is used to ensure that the

reaction foes to completion (100%).

Preparation of Ester

PICTURE Can be prepared by fractional distillation (esterification).

A mixture of glacial carboxylic acid with absolute alcohol (PURE but not AQUEOUS SOLUTION).

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Comparison of Alkanes and Alkenes

Hydrocarbon Alkanes Alkenes

Colour All are colourless

Physical State

Number of carbon 1 – 4 : Gases 5 – 17 : Liquid > 17 : Solid

Number of carbon 2 – 4 : Gases 5 – 15 : Liquid > 15 : Solid

Melting and Boiling Point

Low

Attractive force between the molecules is weak Van der Waal’s force. Thus, only a little amount of heat energy is required to overcome the weak

Van der Waals’ force of attraction.

Increase when going down the group

Number of carbon atoms in the molecule increase. Thus, the molecular size of increases and the weak Van der Waals’ force

of attraction between the molecules become stronger. Thus, more energy is required to overcome the strong Van der Waals’

force of attraction when going down the group.

Density

Low [Less dense than water]

Increase when going down the group

The relative molecular mass of the molecule increase and molecules are packed more closely together.

Solubility (Water) Insoluble

Solubility (Organic Solvent [Benzene])

Soluble

Electrical Conductivity Cannot conduct

Do not contain free mobile ions.

Reaction with Oxygen [Combustion]

Burns with a sooty yellow flame. Burns with a more sooty yellow flame.

Reaction with Bromine [Halogenation]

Brown colour of liquid bromine remains unchanged in alkanes.

Brown colour of liquid bromine is decolourised in alkenes.

Reaction with Acidified Potassium Manganate

(VII) Solution

Purple colour of liquid bromine remains unchanged in alkanes.

Purple colour of liquid bromine is decolourised in alkenes.

Homologous Series [Family]

Characteristics ;-

1. Members can be represented by a general formula.

2. Molecular formula of members differ from other by a –CH2 group [relative molecular mass of 14]

3. Members can be prepared by similar method.

4. Physical properties of members change regularly with increasing number of carbon atoms.

[Melting and boiling points, Physical State, Density]

5. Chemical properties of members are similar as they have the same functional group.

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Isomerism

Isomers have different physical properties BECAUSE they have different structural formula.

Isomers have same chemical properties BECAUSE they have same functional group or belong to

same homologous series.

| | - C - - C - | | | | | | | | | - C - C - C - - C - C - C - C - C - - C - C - C - | | | | | | | | | - C - - C - | |

Straight Chain Branched

Chain

Naming of isomers

- Name the longest and straight carbon chain.

- Name the carbon atoms in this longest chain.

- Locate and name the attached alkyl group. [Position = Number of Carbon atom that is attached]

Organic Compounds Alkanes Alkenes Alcohol

Reasons of Isomerism Different in

carbon chains

Different in carbon chains

Position of double bond

Different in carbon chains

Position of hydroxyl group

Conditions of Longest Chain

- Contain double bond Contain hydroxyl

group

Ways to name the carbon atoms

From the nearest alkyl group

From the nearest double bond

From the nearest hydroxyl group

Number of Isomers

Meth- 0 - 0

Eth- 0 0 0

Prop- 0 0 2

But- 2 3 4

Pent- 3 5 -

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Comparison Between Fats and Oils

Substances Fats

[Butter] Oils

[Palm Oil]

Sources Animal Plant

Physical State [at room temperature]

Solid Liquid

Uses

2. Sources of energy 3. Sources of nutrients 4. Thermal insulation 5. Protection and structural role

Each fat molecule contains 3 fatty acid molecules and 1 glycerol molecule :-

- Fatty acid (is not called carboxylic acid because it is too long) is a carboxylic acid that contains 12

to 18 carbon atoms per molecule

- Glycerol is an alcohol that contains 3 hydroxyl group per molecule – Propane-1,2,3-triol.

Molecular structural of a molecule of fat

PICTURE

Saturated and Unsaturated Fats

The fatty acids can be differentiated in two main ways :-

a. The length of the carbon chain from 12 to 18 carbon atoms

b. The fatty acid may be saturated or unsaturated

* A saturated fatty acid has all carbon-carbon single bond.

Eg. Palmitic acid, stearic acid.

* A unsaturated fatty acid has one or more carbon-carbon double bond.

Monounsaturated fatty acid : One carbon-carbon double bond [Oleic Acid]

Polyunsaturated fatty acid : Two or more carbon-carbon double bond [Lenoleic Acid]

Fats Saturated Fats Unsaturated Fats

Similarities A mixture of different ester formed from a variety of long-chain carboxylic acid called fatty acid with the

alcohol called glycerol.

Differences

Type of Fatty Acids Saturated Unsaturated

Type of Bond Carbon-carbon

Single Bond Carbon-carbon Double Bond

Melting Point High Low

Sources Animal Plant

Physical State Solid Liquid

Cholesterol Content High Low

Converting Unsaturated Fats to Saturated Fats (Hydrogenation)

Bubbling hydrogen gas through hot (180C - 200C) and liquid oil in the presence of nickel or

platinum as catalyst.

As more and more of the double bond get hydrogenated, the relative molecular mass of the oil

molecule increases. Intermolecular force becomes stronger and more energy is needed to overcome

them. The boiling point of the oil increases and the physical state change from liquid to solid.

The hardness of fats produced by hydrogenation depends on the quantity of hydrogen absorbed. The

greater the amount of hydrogen absorbed, the harder the solid fats produced.

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Natural Rubber

Obtained from the latex secreted by rubber tree.

Isoprene (2-methylbuta-1,3-diene) ---(Addition Polymerisation)→ Polyisoprene (Natural Rubber)

H H H

→

H H H | | | | | |

n H - C = C - C = C - H ---- C - C = C - C ----- | | | | H - C - H H | H | H - C - H H | H n

Isoprene (2-methybuta-1,3-diene)

→ Polyisoprene

Natural Rubber has one double bond per repeating unit while isoprene has two double bonds.

Coagulation of Latex

Latex is a colloid (in liquid state but sticky) which consists of rubber particles dispersed in water.

Each rubber particle is made up of many long chains rubber molecule covered with a membrane of

protein which is negatively-charged.

The repulsion between the negatively-charged particles prevents the rubber particles from coming

close to each other. Hence, latex could not coagulate and remain in liquid state.

PICTURE a. ACID (Methanoic acid)

- When an acid is added, the hydrogen ions, H+ neutralise the negative charged on the protein

membrane. The particles can now close together, enabling them to collide with one another

resulting in the breakage of the protein membrane. The rubber molecules combine with one

another and thus causing the latex to coagulate.

b. ALKALI (Ammonia solution)

- When an alkali is added, the latex can be preserved in the liquid state. It contains hydroxide

ions, OH- that neutralise the acid produced by the bacteria. Hence, the rubber particles remain

negatively-charged and the coagulation is prevented.

c. NONE

- When it is exposed to air, the growth and spread of bacteria from the air will produce lactic acid

that causes the coagulation of latex. Due to the slow bacteria action, the coagulation of latex

takes a longer time to occur.

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Vulcanization of Rubber

This process is carried out by

a) Heating natural rubber with sulphur using zinc oxide as catalyst.

b) Immerse natural rubber in the solution of disulphur dichloride, S2Cl2 in methylbenzene.

In vulcanization of rubber, the sulphur atoms are added to the double bond in the natural rubber

molecules to form sulphur cross-links between the rubber particles.

When vulcanized rubber is stretched and released, the cross-linkages pull the chains back to their

original arrangement, improving the elasticity and strength of the rubber.

The presence of sulphur-linkages increases the size of rubber molecules. Therefore, the melting

point of rubber increases, causing vulcanized rubber more resistant to heat and organic solvent

Vulcanized rubber has much less carbon-carbon double bond as compared to unvulcanized rubber.

This explains the higher resistant of vulcanized rubber to oxidation.

PICTURE

The greater the amount of sulphur added, the stronger and harder and more difficult to stretch, but

more elastic (ability to return to its original shape).

Vulcanized Rubber Types of Rubber Unvulcanized Rubber

High Elasticity Low

Hard Hardness Soft

Strong Tensile Strength Weak

Can withstand high temperature

Resistant to Heat Cannot withstand high

temperature

Hard to oxidised Resistant to Oxidation Easy to oxidised