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

Double bonds or not A saturated fat has no C=C double bonds (alkene functional groups) and is usually a solid fat like margarine or animal fat. An unsaturated fat has C=C double bonds and is usually an oil like vegetable oil. 100

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Making margarine To make margarine we have to saturate vegetable oil by bubbling hydrogen gas through the oil. This process is called hydrogenation 103

Is a fat or oil saturated or not? 104

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Hydrolysis When an ester is hydrolysed it goes back to an acid and alcohol We can hydrolyse by adding acid or alkali (NaOH). 107

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Energy changes in chemistry C

Quiz When a chemical reaction takes place heat may be given out or taken in. 1.Can you remember the word we use when heat is given out? 2.Can you remember the word we use when heat is taken in? 111

What do I need to know? 1.Recall and use the terms ENDOTHERMIC and EXOTHERMIC 2.Describe examples of ENDOTHERMIC and EXOTHERMIC reactions. 3.Use simple energy level diagrams to represent ENDOTHERMIC and EXOTHERMIC reactions. 112

Change in energy 113

Definitions 114

Energy level diagrams Heat taken in Heat given out 115

Energy level diagrams EndothermicExothermic Heat taken in Heat given out Energy level of products is higher than reactants so heat taken in. Energy level of products is lower than reactants so heat given out. 116

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Bond enthalpies C

Quick quiz 1.Reactions where the products are at a lower energy than the reactants are endothermic (TRUE/FALSE) 2.Activation energy is the amount of energy given out when a reaction takes place (TRUE/FALSE) 3.A reaction which is exothermic transfers heat energy to the surroundings (TRUE/FALSE) 4.How can we tell if a reaction is exothermic or endothermic? 5.Sketch the energy profile for an endothermic reaction. 6.When methane (CH 4 ) burns in oxygen (O 2 ) bonds between which atoms need to be broken? 120

Answers 1.Reactions where the products are at a lower energy than the reactants are endothermic (TRUE/FALSE) 2.Activation energy is the amount of energy given out when a reaction takes place (TRUE/FALSE) 3.A reaction which is exothermic transfers heat energy to the surroundings (TRUE/FALSE) 4.How can we tell if a reaction is exothermic or endothermic? 5.Sketch the energy profile for an endothermic reaction. 6.When methane (CH 4 ) burns in oxygen (O 2 ) bonds between which atoms need to be broken? FALSE TRUE Measure the temperature change C—H bonds and O=O bonds 121

What do I need to know? 1. Recall that energy is needed to break chemical bonds and energy is given out when chemical bonds form 2. Identify which bonds are broken and which are made when a chemical reaction takes place. 3. Use data on the energy needed to break covalent bonds to estimate the overall energy change for a reaction. 122

Activation energy revisited What is the activation energy of a reaction? The energy needed to start a reaction. BUT what is that energy used for and why does the reaction need it if energy is given out overall? The activation energy is used to break bonds so that the reaction can take place. 123

Burning methane Consider the example of burning methane gas. CH 4 + 2O 2  CO 2 + 2H 2 O This reaction is highly exothermic, it is the reaction that gives us the Bunsen flame. However mixing air (oxygen) with methane is not enough. I need to add energy (a flame). 124

What happens when the reaction gets the activation energy? Bond Forming Bond Breaking Progress of reaction Energy in chemicals O O O O H C H H H O O O O C H HHH O C O O O H H H H 125

Using bond enthalpies By using the energy that it takes to break/make a particular bond we can work out the overall enthalpy/energy change for the reaction. Sum (bonds broken) – Sum (bonds made) = Energy change 126

BIN MIX Breaking bonds is ENDOTHERMIC energy is TAKEN IN when bonds are broken Making bonds is EXOTHERMIC energy is GIVEN OUT when bonds are made. 127

Bond enthalpies BondBond enthalpy (kJ)BondBond enthalpy (kJ) C—H435Cl—Cl243 C—C348C—Cl346 H—H436H—Cl452 H—O463O=O498 C=O804 C=C

Can you work out the energy change for this reaction? 129

The answer is -120 kJ 130

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Challenge question The true value for the energy change is often slightly different from the value calculated using bond enthalpies. Why do you think this is? 135

Example question The calculated value is 120 kJ 136

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Definitions Write each of these phrases in your book with a definition in your own words: Exothermic reaction Endothermic reaction Activation energy Catalyst Bond energy/enthalpy 138

How did you do? Exothermic reaction A reaction which gives energy out to the surroundings. Endothermic reaction A reaction which takes in energy from the surroundings. Activation energy The energy required to start a reaction by breaking bonds in the reactants Catalyst A substance that increases the rate of a reaction by providing an alternative pathway with lower activation energy. It is not used up in the process of the reaction Bond energy/enthalpy The energy required to break a certain type of bond. The negative value is the energy given out when that bond is made. 139

Popular exam question 1.Explain why a reaction is either exothermic or endothermic?

Popular exam question 1.Explain why a reaction is either exothermic or endothermic? ①In a chemical reactions some bonds are broken and some bonds are made. ②Breaking bonds takes in energy. ③Making bonds gives out energy. ④If the energy given out making bonds is higher than the energy needed to break them the reaction is exothermic. ⑤If the energy needed to break bonds is higher than the energy given out making them the reaction is endothermic. 141

Chemical Equilibria C7.3 Reversible Reactions & Dynamic Equilibria 142

What do I need to know? 1.State that some chemical reactions are reversible 2.Describe how reversible reactions reach a state of equilibrium 3.Explain this using dynamic equilibrium model. 143

Reversible or not reversible Until now, we were careful to say that most chemical reactions were not reversible – They could not go back to the reactants once the products are formed. 144

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Reversible Some chemical reactions, however, will go backwards and forwards depending on the conditions. CoCl 2 ·6H 2 O(s)  CoCl 2 (s) + 6H 2 O(l) pink blue 146

How do we write them down? This is the symbol for used for reversible reactions. CoCl 2 ·6H 2 O(s) CoCl 2 (s) + 6H 2 O(l) 147

What is equilibrium? 148

Dynamic Equilibrium. 149

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Dynamic Equilibria C7.3 Controlling equilibria 152

What do I need to know? 1. Recall that reversible reactions reach a state of dynamic equilibrium. 2. Describe how dynamic equilibria can be affected by adding or removing products and reactants. 3. Explain the difference between a “strong” and “weak” acid in terms of equilibria 153

Position of the equilibrium Equilibrium can “lie” to the left or right. This is “in favour of products” or “in favour of reactants” Meaning that once equilibrium has been reached there could be more products or more reactants in the reaction vessel. 154

Le Chatelier’s principle If you remove product as it is made then equilibrium will move to the right to counteract the change If you add more reactant then equilibrium will move to the right to counteract the change. In industry we recycle reactants back in and remove product as it is made to push the equilibrium in favour of more product. 155

Complete When a system is at__________ to make more product you can_________ product or add more __________ for example by recycling them back in. To return to reactants you ______ product or remove_________. [equilibrium, add, reactant, remove, product] 156

Strong and weak acids 157

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Practicing definitions Write each of these phrases in your book with a definition in your own words: Reversible reaction Dynamic equilibrium Position of equilibrium Strong acid Weak acid 162

How did you do? Reversible reaction A reaction that can proceed in the forward or reverse directions (represented by two arrows in an equation). Dynamic equilibrium The point where the rate of the forward reaction = rate of the reverse reaction. Position of equilibrium The point where there is no further change in the concentration of either reactants or products. The position can lie to the left (favouring reactants) or right (favouring products). Strong acid An acid that is completely dissociated in water Weak acid An acid that is only partly dissociated in water because the reaction is in dynamic equilibrium and favours the reactants (LHS). 163

Popular exam question 1.Ethanoic acid (CH 3 COOH) is a weak acid but hydrochloric acid is a strong acid. Use ideas about ion formation and dynamic equilibrium to explain this difference

Popular exam question Ethanoic acid (CH 3 COOH) is a weak acid but hydrochloric acid is a strong acid. Use ideas about ion formation and dynamic equilibrium to explain this difference. ①Hydrochloric acid ionises completely ②So hydrogen ion concentration is high ③Ethanoic acid only partly dissociates because the reaction is reversible ④Equilibrium is mainly to the left ⑤So hydrogen ion concentration is low. 165