Study Smart Chapter 2 f5

STUDYSMART CHEMISTRY FORM 5 CHAPTER 2 : CARBON COMPOUND 2.1 Understanding carbon compounds

2.2 Analysing Alkanes 2.3 Analysing Alkenes

2.4 Synthesising ideas on isomerism 2.5 Analysing Alcohols

2.6 Analysing carboxylic acids 2.7 Analysing esters

2.8 Evaluating fats

2.9 Analysing natural Rubber

2.10 Creating awareness of order in homologous series

2.11 Expressing gratefulness for the variety of organic materials in nature 2.1 UNDERSTANDING CARBON COMPOUNDS

Carbon compound are compound that containing carbon

Carbon compound can be classified into inorganic and organic carbon compound.

Examples of inorganic carbon compound (usually non-living things)

- Carbon Monoxide, CO

- Carbon Dioxide, CO

- Calcium Carbide, CaC

- Carbonate salts for example Na

CO

, CaCO

CuCO

Examples of organic carbon compound (usually living things)

- Urea

- Natural rubber

- Glucose

- Protein

- Cellulose

- Ethanol

- Starch

- Glucose

Hydrocarbon are organic compound containing hydrogen and carbon only

Organic compound in which some or all of the hydrocarbon atoms have been replaced

other atoms are called non-hydrocarbons.

Hydrocarbon molecules that are made entirely of carbon-carbon single bonds are said

to be saturated hydrocarbon. Hydrocarbon containing at least one carbon-carbon

double or triple bonds is referred as unsaturated hydrocarbon.

Combustion product of organic compounds

- When an organic compound is burnt in excess oxygen, the main product are CO

and ,

H

O.

Example : Combustion of glucose, C

H

O

2.2 ANALYSING ALKANES

Usually in fuels, examples: natural gas, petrol, diesel Are homologous series

Have a formula of CnH2n+2, where n is a positive integers.

Example : propane has three carbon atom, thus n=3. Then the formula of propane is C3H8

Ends with suffix –ane

Next alkane formula differ by –CH2 atoms. Eg: methane: CH4, ethane: C2H6

Structure of Alkanes

Shows how all atoms in a molecule joined together by drawing lines between atoms to represent the bonds

Example: butane has a formula of C4H10, therefore the structural formula is:

It has 4 carbon atoms bonded together with 10 hydrogen atoms. All alkanes are saturated. All alkenes are unsaturated

Name of carbon atoms are shown in table below

Complete the table on left and below

n Name Molecular

Formula

Structural Formula

1 Methane CH4

2 Ethane

Name of carbon atom Root name

1 Meth- 2 Eth- 3 Prop- 4 But- 5 Pent- 6 Hex- 7 Hept- 8 Oct- 9 Non- 10 Dec-

3 Propane 4 Butane 5 Pentane 6 Hexane 7 Heptane 8 Octane

9 Nonane

10 Decane

Physical properties of alkanes are :-

- Melting points and boiling points increase as the bonds become larger and heavier which increases the forces of attraction between molecules so more energy (from heat) is needed to separate them with the increase of strength of forces of attraction

- Alkanes are insoluble in water but soluble in organic solvents such as tetrachloromethane as a alkanes are organic compounds

- Alkane density increases down the series; all alkenes are less than 1g/cm3

- Alkanes become more viscous (uneasily flow) going down the series as the longer molecules tangles together when it flows

- Alkanes become less flammable down the series as B.P. becomes larger

- Alkanes are unreactive with either metals, water, acids or bases because the C – C and C – H covalent bonds are harder to break

Alkane Formula Boiling point [°C] Melting point [°C] Density [g·cm3] (at 20°C)

Methane CH4 -162 -183 gas Ethane C2H6 -89 -172 gas Propane C3H8 -42 -188 gas Butane C4H10 0 -138 gas Pentane C5H12 36 -130 0.626(liquid) Hexane C6H14 69 -95 0.659(liquid) Heptane C7H16 98 -91 0.684(liquid) Octane C8H18 126 -57 0.703(liquid) Nonane C9H20 151 -54 0.718(liquid) Decane C10H22 174 -30 0.730(liquid)

Chemical properties of alkanes

Alkanes are unreactive compound

Alkanes burn in air to ALWAYS form carbon dioxide and water. 2C4H10(g) + 13O2(g)  8CO2(g) + 10 H2O (l)

When there is insufficient oxygen, the product is ALWAYS carbon monoxide and unburnt carbon.

2CH4 (g) + 3O2 (g)  2CO(g) + 4H2O

CH4 (g) + O2 (g)  C(g) + 4H2O

Example: Butane is commonly used camping gas.

High alkanes burn less completely and gives soot (unburnt carbon) and CO HALOGINATION / SUBSTITUTION REACTION

Reaction of alkanes with halogens (Cl2, Br2, and I2)

Light is needed to break covalent bond between halogens molecule atoms

Substitution reaction – the reaction in which one or more atoms replace other atoms in a molecule

Example : Mixture of methane, CH4 and chlorine is exposed to UV light

CH4 + Cl2  CH3Cl + HCl monochloromethane CH3Cl + Cl2  CH2Cl2 + HCl dichloromethane CH2Cl2 + Cl2  CHCl3 + HCl trichloromethane CHCl3 + Cl2  CCl4 + HCl tetrachloromethane 2.3 ANALYSING ALKENES

Have general formula CnH2n.

All alkene names end with –ene.

The formula of one alkene differs from the next by –CH2.

Have similar properties like alkane going down the series.

Example : butene has a formula of C4H8, therefore the structural formula is:

It has 4 carbon atoms with a double bond bonded together with 8 hydrogen atoms. All alkenes are unsaturated

The Importance of Ethene - Ethanol – solvent & fuel

- poly(ethene) – PE plastic variations - Ethanoic acid – vinegar

n Name Molecular Formula

Structural Formula 1 Methane

METHENE IS NOT IN ALKENES GROUP SINCE ITS CONTAIN SINGLE CARBON ATOM THUS, NO DOUBLE BOND.

2 Ethane C2H4 3 Propane 4 Butane 5 Pentane 6 Hexane

7 Heptane

8 Octane

9 Nonane

10 Decane

Physical properties of alkenes are - cannot conduct electricity - Less dense than water

- Obeys “like dissolve like” rule where it dissolve in organic solvent but insoluble in water - Alkenes have low melting and boiling points

Chemical Reaction of Alkenes

Alkenes are chemically more reactive than alkanes due to the presence of the C = C double bond.

COMBUSTION

Burns in air to form carbon dioxide and water Example: Ethene burns in air.

C2H4(g ) + 3O2(g)  2CO2(g) + 2H2O (l)

To differentiate the percentage of carbon in alkene and alkane C2H4(g ) + 3O2(g)  2CO2(g) + 2H2O (l)

Alkenes burn with sootier flame as compared to alkanes. This is because alkenes have a higher percentage of carbon in their molecules.

For ethane, C2H4 % of carbon = 2 x 12 . x 100% 2(12) + 4(1) = 24 x 100% 28 = 85.71 % For ethane, C2H6 % of carbon = 2 x 12 . x 100% 2(12) + 6(1) = 24 x 100% 30 = 80 % ADDITION REACTION

I) Addition of hydrogen, H2 / Hydrogenation [ethane  ethane]

C2H4 + H2 ---> C2H6

Ethene ---> Ethane II) Addition of halogens (Bromine, Br2)

Ethene + Br2 ---> 1,2-dibromoethane

III) Addition of hydrogen halides

IV) Addition of water, H2O / Hydration [ alkene  alcohol ]

V) Addition of hydroxyl groups, -OH

- Acidified potassium manganite (VII), KMnO4

Ethene + H2O + [O] ---> Ethane-1,2-diol

POLYMERIZATION

2.4 SYNTHESISING IDEAS ON ISOMERISM

Isomers are compound with the same molecular formula but different structural formula Examples :

1. Isomers of pentane

2. Isomers of butane

Naming of each isomer is based on IUPAC. There are several steps before naming an isomers STEP 1 : Specify the number of carbon atom in the largest continuous carbon chain

STEP 2 : Numbering carbon atoms with 1,2,3,…. Starting near functional group / and branch. STEP 3 : Branch names, -CH3, methyl

-CH2CH3, ethyl Examples : Isomer of Pentene Isomer of Hexane Isomer of Butane Isomer of Butene

2.5 ANALYSING ALCOHOLS

The general formula of alcohol is CnH2n+1OH (n = 1,2,3)

Alcohol contain the hydroxyl group (-OH) as the functional group that covalently bonded to a carbon atom

Naming of alcohol

- Root – denotes the number of carbon atom (meth-, eth-, prop-…) - Ending – replace –e from the name of the alkane with –ol

NUMBER OF CARBON ATOM MOLECULAR FORMULA

STRUCTURAL FORMULA NAME

1 CH2OH Methanol 2 3 4 5 6

Naming alcohol based on IUPAC

STEP 1 : Identify the longest carbon chain containing the hydroxyl group

Root – obtain from the number of carbon atom in the longest carbon chain

STEP 2 : Identify the position pf hydroxyl group by numbering the carbon atom in the longest chain

Beginning at the end nearer to the hydroxyl group

STEP 3 : identify and name that attracted alkyl group (branch) –prefix STEP 4 : Complete the name by combining the three component Examples : 1. 2 Name : _____________________ Name : _____________________ 3. 4. Name : __________________________________ Name : ____________________________ Isomerism in alcohol exists in the alcohol with three or more carbon atoms

Examples :

1. Propanol (C3H7OH)

Preparation of Ethanol

Industrial production of ethanol

i) from sugar and starch by fermentation ii) from petroleum fractions by hydration H3PO4

CH2 = CH2 + H2O CH3CH2OH

300oC / 60 atm Laboratory preparation of ethanol

In the fermentation process, the zymase enzyme decompose the glucose to form ethanol and carbon dioxide

Equation of the fermentation process : zymase

C6H12O6 2C2H5OH + 2CO2

30oC -4 oC

Reacting ethane with steam to produce alcohol (fractional distillation)

Ethene and steam are passed over phosphoric acid H3PO4 (as a catalyst) under high temperature

of 300oC and pressure of 65 atm.

C2H4(g) + H2O(g)  C2H5OH(aq)

Since this is reversible reaction, both ethene and water are produced aside from ethanol. The ethanol is separated by fractional distillation.

Physical properties of alcohol :

A simple alcohol are liquids and very soluble in water

As the number of carbon atoms in their molecules increases, the molecules get bigger, the forces of attraction between molecules becomes stronger, more energy needed to overcome the forces of attraction. Thus, melting and boiling points increase gradually.

Physical properties of ethanol are :-

- colourless liquid - sharp smell

- complete miscible with water - boiling point : 78oC at 1atm Chemical properties of ethanol

COMBUSTION

* Complete combustion of alcohol produces carbon dioxide and water C2H5OH + 3O2  2CO2 + 3H2O

* Release lots of heat, use as a fuel C4H9OH + 6O2  4CO2 + 3H2O

OXIDATION

* Alcohol can be easily oxidized to carboxylic acid by using oxidizing agent

* Oxidising agent : acidified potassium manganat(VII) – colour turns from purple to green acidified potassium dichromate(VI) – colour turns from orange to green * Ethanol undergo oxidation reaction to form ethanoic acid

[ -CH2OH group has removed 2 hydrogen atoms and gained an oxygen atom]

C2H5OH + 2[O]  CH3COOH + 3H2O

Ethanol carboxylic acid Draw the structural formula :

DEHYDRATION

* Involves the removal of water by using catalyst such as heated porcelain chips, porous pot, aluminium oxide, concentrated sulphuric acid

* The dehydration of ethanol produces ethane and water heated

C2H5OH C2H4 + H2O

Uses of alcohol

As a fuel – Volatile, highly flammable and high content

As a solvent and thinner – colourless, volatile, miscible with water and good organic solvent As a raw material to make pharmaceutical products – volatile, good solvent, and antiseptic 2.6 ANALYSING CARBOXYLIC ACIDS

Common carboxylic acid in nature are acetic acid in vinegar, lactic acid in sour milk, citric acid in citrus fruits.

Contain the element carbon, hydrogen and oxygen.

When comparing to alcohols, carboxylic acids contain 2 oxygen atoms Functional group for carboxylic acid is carboxyl group, -COOH or

General formula of carboxylic acid is CnH2n+1COOH, where n = 0,1,2,3,….

Straight chain carboxylic acids are named with ending –oic acid

n Number of C atom (s) Molecular Formula Structural Formula Name

0 1

HCOOH Methanoic Acid

1 2

2 3

3 4

5 6

6 7

Naming the branches carboxylic acid

- Identify the longest carbon chain containing the carboxyl group - Number the carbon atom beginning at the carboxyl group Examples

___________________ ___________________ ___________________ Making ethanoic acid

Laboratory preparation – by the oxidation of ethanol by using oxidizing agent (Acidified KMnO4

or K2Cr2O7 solution)

Physical properties of ethanoic acid - a colourless liquid at room temperature - a sour smell

- very soluble in water

Chemical Properties of Carboxylic acids

Ethanoic acid is a weak monoprotic acid. Hydrogen atoms from carboxyl group, -COOH can be ionize in water to form hydrogen ions

Reaction with reactive metals, bases and carbonates (Act as acid) CH3COOH + Mg 

CH3COOH + NaOH 

Reaction with alcohols to form ester and water (Esterification)

A mixture of carboxylic acid and alcohol with a few drops of concentrated sulphuric acid is heated, an ester is formed.

Example

2.7 ANALYSING ESTERS

General formula of ester is CnH2n+1COOCmH2m+1

Functional group in ester is called carboxylate group, -COO or Naming ester Formation of ester i) ___________________ ii) _______________ _________________ _____________________ Physical properties of ester

- has sweet pleasant smell (fruity smell) - a colourless liquid

- low melting and boiling points

- slightly soluble in water but readily dissolve in organic solvent Carboxylic acid + Alcohol Ester + Water

H2SO4

GENERAL CONCLUSION FOR ALKANE, ALKENE, ALCOHOL, CARBOXYLIC ACID AND ESTER

2.8 EVALUATING FATS

Fats are found in animals which is solid at room temperature. Example : butter, tallow Oils are found in plants which is liquid at room temperature. Example : palm oil, sunflower oil Fats and oils are ester formed from glycerol (alcohol with 3 hydroxyl group) and fatty acids (long-chain carboxylic acids)

Chemical equation :

Saturated and Unsaturated fats Saturated fats

- saturated alkyl group ( contains single covalent bond only) - Glycerol and saturated fatty acids, only contain carbon – carbon single bond

- Animal fats contain large proportion of saturated esters, have high melting points and solid in room temperature

- Example : Tristearin, tripalmitin Unsaturated fats

- unsaturated alkyl group ( contains one or more carbon – carbon double bonds.

- Glycerol and unsaturated fatty acids contain one or more carbon – carbon double bonds. - Plant / vegetable oils contain a large proportion of unsaturated ester, have lower melting

Fermentation Esterification Oxidation dehydration Hydration Hydrogenation Alkane CnH2n+2 Alkene CnH2n Alcohol CnH2n+1OH Glucose C6H12O6 Carboxylic Acid CnH2n+1COOH Ester CnH2n+1COOCmH2m+1 R1 , R2 , and R3 : same or different alkyl group

points, and liquids at room temperature. - Example : Triolein

Converting unsaturated fats to saturated fats - by hydrogenation process

- Margarine is made by hydrogenating some of the carbon – carbon double bonds in polyunsaturated vegetable oil so that the physical state changes from liquid to soft. Industrial extraction of palm oil

2.9 ANALYSING NATURAL RUBBER

A polymer is a large molecules consisting of a long chain. It is made by joining together many small molecules called monomers

Natural polymers exist naturally. Below are the examples of natural polymers and their monomers.

Natural rubber is actually poly(isoprene)

Its monomer is 2-methyl-1,3-diene or isoprene with molecular formula C5H8

The isoprene molecules undergo addition polymerization to produce a long chain molecules called poly(isoprene)

Latex is a white milk-like fluid

Rubber particles is made up of many long-chain rubber molecules enclosed by a protein-like membrane 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

Latex will coagulate when

- An acid is added. (Methanoic acid or ethanoic acid) - Exposed to air

Coagulation process of latex

a) When an acid is added, the hydrogen ions neutralize the negative charges on the protein membrane.

b) The rubber particles can now come closer together and collide with one another resulting in the breakage of the protein membrane

c) The rubber molecules combine with one another and entangle thus causing the latex to coagulate.

Latex will coagulate when it is exposed to air because the growth and spread of bacteria produce lactic acid.

Natural Polymer Monomer Natural Rubber Isoprene

Starch Glucose

Cellulose Glucose Protein Amino Acid

Latex can be preserved in the liquid by adding ammonia solution. Ammonia solution contain hydroxide ions that neutralize the acid produced by bacteria

Vulcanization of rubber

Properties of natural rubber : - Soft

- Elasticity decrease over time - Sensitive to heat

- Easily oxidized by air

The properties can be improved through vulcanization process. Vulcanization process can occur when

a) latex is heated with sulphur (industry)

b) rubber products are exposed to disulphur dichloride, S2Cl2 gas (industry)

c) by soaking natural rubber in the solution of disulphur dichloride in methylbenzene. (Laboratory preparation)

The presence of cross-linkage of sulphur atoms between the rubber molecules improves the properties of rubber.

Uses of natural rubber

a) making tyres, footwear, rubber threads, rubberized bitumen roads b) Gloves, tubes and hoses

c) insulator of electrical appliance and cables

Vulcanized rubber Difference Unvulcanized rubber

More elastic Elasticity Less elastic

Harder Hardness Softer

Stronger Tensile strength Weaker

Can withstand higher temperature

Resistance on heat Cannot withstand higher temperature

Hard to be oxidized Resistance to oxidation Easily oxidized Does not become soft

and sticky easily

Effect of organic solvent Becomes soft and sticky easily