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, CO2 - Calcium Carbide, CaC2 - Carbonate salts for example Na2CO3, CaCO3, CuCO3 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 CO2, and , H2O. Example : Combustion of glucose, C6H12O6 C6H12O6 + 6O2  6CO2 + 6H2O

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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 Name of carbon atom Root name Complete the table on left and below 1 Meth2 Eth3 Prop4 But5 Pent6 Hex7 Hept8 Oct9 Non10 Decn Name Molecular Structural Formula Formula 1 Methane CH4

2

Ethane

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3

Propane

4

Butane

5

Pentane

6

Hexane

7

Heptane

8

Octane

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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 Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane

Formula CH4 C2H6 C3H8 C4H10 C5H12 C6H14 C7H16 C8H18 C9H20 C10H22

Boiling point [°C] -162 -89 -42 0 36 69 98 126 151 174

Melting point [°C] -183 -172 -188 -138 -130 -95 -91 -57 -54 -30

Density [g·cm3] (at 20°C) gas gas gas gas 0.626(liquid) 0.659(liquid) 0.684(liquid) 0.703(liquid) 0.718(liquid) 0.730(liquid)

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Chemical properties of alkanes

Alkanes are unreactive compound Chemical properties of alkanes COMBUSTION 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 Complete the table below 5 Study Smart www.studysmart.page.tl

n

Name

1

Methane

Molecular Formula

Structural Formula

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

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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) Incomplete combustion forms soot and CO. It’s produced more than alkane 7 Study Smart www.studysmart.page.tl

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

Ethene

+ HCl -----------> Chloroethane

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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 The joining of several identical alkene molecules to form a big molecule.

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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

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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 1

MOLECULAR FORMULA

STRUCTURAL FORMULA

CH2OH

NAME

Methanol

2

3

4

5

6

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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)

2. Butanol

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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 o o 30 C -4 C 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 * Ethanol burns with a non-smoky blue flame 13 Study Smart www.studysmart.page.tl

* 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 Porcelain chips

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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 0

Number of C atom (s) 1

Molecular Formula

HCOOH

1

2

2

3

3

4

4

5

Structural Formula

Name

Methanoic Acid

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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  CH3COOH + Na2CO3  16 Study Smart www.studysmart.page.tl

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. Carboxylic acid + Alcohol

Ester + Water H2SO4

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

Ending -yl

Ending -oate

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 17 Study Smart www.studysmart.page.tl

GENERAL CONCLUSION FOR ALKANE, ALKENE, ALCOHOL, CARBOXYLIC ACID AND ESTER Glucose C6H12O6 Fermentation

Alkane CnH2n+2

Hydrogenation

Hydration

Alkene CnH2n

dehydration

Alcohol CnH2n+1OH

Oxidation

Carboxylic Acid CnH2n+1COOH

Esterification

Ester CnH2n+1COOCmH2m+1 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 :

R1 , R2 , and R3 : same or different alkyl group

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 18 Study Smart www.studysmart.page.tl

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 [Refer Textbook]

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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 Polymer Monomer Natural Rubber Isoprene Starch Glucose Cellulose Glucose Protein Amino Acid 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.

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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 Limit its uses - 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.

Vulcanized rubber More elastic Harder Stronger Can withstand higher temperature Hard to be oxidized Does not become soft and sticky easily

Difference Elasticity Hardness Tensile strength Resistance on heat Resistance to oxidation Effect of organic solvent

Unvulcanized rubber Less elastic Softer Weaker Cannot withstand higher temperature Easily oxidized Becomes soft and sticky easily

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

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