Organic Chemistry Structures 1

What do I need to know? 1.Translate between molecular, structural and ball and stick representations of simple organic molecules 2.Describe how the functional group affects the property of an organic compound and understand that alkanes are unreactive towards aqueous reagents because C—C and C—H bonds are unreactive; 3.Write balanced chemical reactions including for burning hydrocarbons including state symbols 2

Representations of organic molecules There are a number of different ways to represent organic molecules. Ball and stick – this is just like molymods 3

Representations of organic molecules Structural formula – this is where we show the covalent bonds between atoms as a line Semi-structural (molecular) – this is where we write out the formula but do not include bonds; these are implied eg CH 3 CH 2 OH 4

Molecular formula – this simply counts the numbers of each sort of atom present in the molecule, but tells you nothing about the way they are joined together. Eg C 2 H 6 O This is the least helpful type of formula as it could be one of two (or more) different chemicals 5

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Rules of organic molecules Generally speaking Carbon must make four bonds Nitrogen must make three bonds Oxygen must make two bonds Hydrogen must make one bond A double bond counts as two bonds eg C=C or C=O. A triple bond counts as three bonds. 8

AfL - Quiz 1.Draw the structural formula for butanol 2.Write the molecular formula for butanol 3.Draw the structural formula for hexane 4.Write the molecular formula for hexane 5.Write the molecular formula for an alkane with 25 carbon atoms. 6.How many bonds does oxygen make in methanol? 7. Give an example of a use for ethanol 8. Give an example of a use for methanol 9

1.Butanol 2.C 4 H 10 O 3.Hexane 4.C 6 H 14 5.C 25 H Fuel/feedstock for synthesis/solvent/used in perfume 8.Solvent, antifreeze, feedstock for adhesives and plastics 10

Understanding reactivity Alkanes are unreactive towards aqueous reagents because C-C and C-H bonds are unreactive. What about organic molecules that have different bonds? We call families of different types of bonded atoms FUNCTIONAL GROUPS An example is the –OH group or alcohol group. 11

Different functional groups NameFunctional groupProperties AlkaneC-HRelatively unreactive, burns in air due to hydrocarbon chain AlkeneC=CUsed as a feedstock to make polymers Alcohol-OHGood solvent, volatile, burns in air due to hydrocarbon chain Carboxylic acid-COOHWeak acid such as vinegar EsterRCOOR’Have distinctive smells such as fruits 12

Alkanes and combustion Because of the hydrocarbon chain alkanes burn readily releasing large amounts of energy. Alkanes are therefore used as fuels. When they burn completely they make carbon dioxide and water. eg octane (found in petrol) C 8 H ½ O 2  8CO 2 + 9H 2 O 13

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Balanced chemical equations Write the balanced chemical equation for burning ethanol in air as a fuel and burning pentane as a fuel (include state symbols). 18

Answers Ethanol 2C 2 H 5 OH(l) + 6O 2 (g)  4CO 2 (g) + 6H 2 O(l) Pentane C 5 H 12 (l)+ 8O 2 (g)  5CO 2 (g) + 6H 2 O (l) 19

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Alcohols and the Manufacture of Ethanol C7.1 and C7.5 22

What do I need to know? 1. The characteristic properties of alcohols are due to the presence of an –OH functional group 2. Know a range of methods for synthesising ethanol and limitations of fermentation reactions 3. Be able to explain why bioethanol is important for sustainability 23

Functional groups - reminder Look back at your table of functional groups. Write a short paragraph to explain why different organic chemicals have different properties in terms of functional groups. Use examples such as “carboxylic acids are acidic because they have a –COOH group”. 24

Can you recognise the functional group? Circle which of these are alcohols? 25

Answer Alcohols have an –OH group 26

Properties and uses of alcohols Properties: volatile liquid (evaporates quickly at room temperature – more than water) colourless burns readily in air because of the hydrocarbon chain good solvent 27

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Uses of ethanol and methanol Ethanol: biofuels, solvents, feedstock for synthesis Methanol: cleaner, feedstock for synthesis Feedstock is the name we give to an “ingredient” on a chemical plant 30

Reactions of different functional groups This is illustrated very well by comparing the reaction of sodium with ethanol, hexane and water. You have seen this reaction. Fill in the following table and compare with the mark scheme: 31

Observations with sodium 32

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Comparing functional groups 34

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How do we make ethanol? Fermentation is a key process for obtaining ethanol. It is relatively cheap and requires wheat or beet sugar. The process involves the anaerobic respiration of yeast at temperatures between 20 and 40°C and at pH 7. 36

Conditions for fermentation 37

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How do we obtain a concentrated solution? Ethanol has a different boiling point to water. We can therefore separate water and ethanol using distillation. 44

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Making ethanol using ethane from crude oil Ethane to ethene by CRACKING C2H6  CH2=CH2 zeolite catalyst OR heat Ethene to ethanol by reaction with STEAM CH2=CH2 + H 2 O  CH3CH2OH phosphoric acid catalyst 47

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Working out masses We can use the useful relationship Where Mr is the molecular mass eg Mr of ethane C 2 H 6 is (2 X 12) + (6 x 1) = 30 50

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Explanation In this question every ethene molecule that reacts makes one molecule of ethanol. We need to relate the number of molecules to mass using our equation. Mass 1 is mass of ethene = 1 tonne Mr 1 is Mr of ethene = 28 Mass 2 is mass of ethanol = ? Mr 2 is Mr of ethanol = 46 52

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Other alternatives Ethanol has also been synthesised using genetically modified e-coli bacteria and sugars from seaweed. This process is sustainable as the seaweed and bacteria are renewable sources Like yeast, bacteria can be killed by high concentrations of alcohol and high temperatures 56

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Ethanol – Key facts Ethanol is made on an industrial scale as a fuel, a solvent and as a feedstock for other processes; There is a limit to the concentration of ethanol solution that can be made by fermentation and there are optimum conditions of pH and temperature. Ethanol solution can be concentrated by distillation to make products such as whisky and brandy; Genetically modified E. coli bacteria can be used to convert waste biomass from a range of sources into ethanol and recall the optimum conditions for the process; Ethane from crude oil can be converted into ethanol Evaluating the sustainability of each process is important. 59

Plants photosynthesise Remove CO 2 from atmosphere Fermentation produces ethanol fuel Burning Releases CO 2 into atmosphere Replanting Photosynthesis removes CO 2 Bioethanol cycle 60

Balancing carbon cycle equations 61

Balancing carbon cycle equations 62

Balancing carbon cycle equations 63

Carboxylic acids C7.1 64

What do I need to know? 1.understand that the properties of carboxylic acids are due to the presence of the –COOH functional group; 2.recall the names and formulae of methanoic and ethanoic acids; 3.recall that many carboxylic acids have unpleasant smells and tastes and are responsible for the smell of sweaty socks and the taste of rancid butter; 4.understand that carboxylic acids show the characteristic reactions of acids with metals, alkalis and carbonates; 5.recall that vinegar is a dilute solution of ethanoic acid. 65

Can you recognise the functional group? Circle which of these is a carboxylic acid? 66

Answer This is a carboxylic acid 67

Methanoic and Ethanoic Methanoic acidEthanoic acid (VINEGAR) 68

Organic or CARBOXYLIC acids are part of life itself and can be found in many animals and plants. Many acids are part of life itself, they are known as CARBOXYLIC acids Acids in nature 69

Reactions of carboxylic acids Reaction of carboxylic acids 1) Acid + metal  salt + hydrogen Ethanoic acid + magnesium  magnesium ethanoate + hydrogen 2) Acid + metal oxide  salt + water Ethanoic acid + copper oxide  copper ethanoate + water 3) Acid + metal carbonate  salt + water + carbon dioxide Ethanoic acid + sodium carbonate  sodium ethanoate + water + carbon dioxide 70

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Esters, Fats and Oils C7.1 77

What do I need to know? 1. Recall the method for producing an ester using reflux 2. Describe how fats and oils are all types of ester and explain how margarine is made 3. Explain how bromine water can be used to test whether a fat is saturated or unsaturated. 78

Making esters What type of organic chemicals do you need to mix together? Can you name the ester made from ethanoic acid and methanol? 79

Making esters What type of organic chemicals do you need to mix together? A carboxylic acid and an alcohol with an acid catalyst Can you name the ester made from ethanoic acid and methanol? Methyl ethanoate 80

Esters 81

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Making esters RefluxDistillationPurificationDrying 84

Reflux apparatus 85

How do I describe reflux for an exam? 1.Mixture heated in flask (1) … 2.with condenser above (1) … 3.so no liquid is lost by evaporation and allows longer time for the reaction (1) 86

Distillation 87

Describing distillation 1.The mixture is heated 2.At the boiling point of the ester is becomes a vapour 3.The vapour is condensed in the condenser 4.The liquid is collected 88

Purification 1.Collected ester is shaken in a separating funnel with distilled water. 2.Impurities dissolve in the water 3.Impurities are tapped off Ester 89

Drying 1.Solid drying agent is added to the product 2.This could be calcium chloride or sodium sulphate 3.This removes water from the product 90

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Fats and oils These are a special type of ester made from glycerol and fatty acids. 97

Fats and oils Removal of water in the condensation reaction makes a fat or oil 98

Saturated or unsaturated? Have you heard these terms on the television? Vegetable oil is mostly unsaturated Animal fat is mostly saturated 99