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What are CFCs? CFC stands for chlorofluorocarbon. CFCs are a family of compounds that contain only chlorine, fluorine and carbon atoms. Here are some examples: CCl 2 F 2 Cl 2 FC-CCl. F 2 Dichlorodifluoromethane 1, 1, 2 -trichloro-1, 2, 2 trifluoroethane 3 of 51 © Boardworks Ltd 2009

Naming CFCs 4 of 51 © Boardworks Ltd 2009

What are the properties of CFCs? CFCs contain strong covalent bonds. This means that they are very inert (unreactive). CFCs therefore last for a long time in the environment as they don’t decompose or react with other substances easily. They are also insoluble in water, and have low melting and boiling points. boiling point: – 30°C melting point: – 158°C boiling point: 48°C melting point: – 35°C What state are these CFCs at room temperature? 5 of 51 © Boardworks Ltd 2009

What are CFCs used for? During the 1930 s, an American engineer named Thomas Midgely discovered that CFCs were suitable for use as coolants in refrigerators. This was a very useful discovery because the refrigerants used previously were toxic compounds like ammonia and sulfur dioxide. In the 1960 s, other uses for CFCs started to be found: as propellants for aerosol cans and to inject bubbles into plastic to make foams for insulation. 6 of 51 © Boardworks Ltd 2009

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What is the ozone layer The ozone layer is a portion of the stratosphere (upper atmosphere). It contains the gas ozone (O 3) which absorbs ultraviolet (UV) radiation emitted from the Sun. There is strong evidence that UV radiation is harmful. Scientists believe that it causes skin cancer and cataracts, and can also damage plants and micro-organisms. In the late 1970 s and early 1980 s, scientists noticed that the ozone layer was being depleted. 8 of 51 © Boardworks Ltd 2009

How was the CFC problem discovered? 9 of 51 © Boardworks Ltd 2009

How do CFCs react with ozone? 10 of 51 © Boardworks Ltd 2009

How do CFCs react with ozone? The chlorine free radical is actually a chlorine atom. It is extremely reactive because it has seven outer electrons – one short of a full shell. Chlorine free radicals react with ozone: Cl • + O 3 Cl. O • + O 2 The reaction produces another free radical species: Cl. O • . This can also react with ozone: Cl. O • + O 3 Cl • + 2 O 2 This process forms a chain reaction: chlorine free radicals are used up in the first step, but then re-produced in the second step. 11 of 51 © Boardworks Ltd 2009

CFCs and chain reactions Chlorine free radicals are regenerated in the second step of the chain reaction, therefore a single chlorine radical can destroy 100, 000 ozone molecules. This image shows the amount of ozone over Antarctica. Dark blues and purples indicate low levels of ozone. How has the ozone layer changed? 12 of 51 © Boardworks Ltd 2009

Is ozone depletion slowing? In the 1980 s, scientists discovered that ozone was being destroyed by the chlorofluorocarbons (CFCs) widely used in aerosols and refrigerators. CFCs can stay in the environment for 50 years, destroying ozone long after they are produced. However, international regulations to reduce CFC emissions may be helping to repair the ozone layer. Studies in 2006 showed that the hole in the ozone layer is not getting bigger. It is possible that if CFCs remain banned, the ozone layer could return to normal levels. 13 of 51 © Boardworks Ltd 2009

What are the alternatives to CFCs? Two families of compounds are now used in place of CFCs: l hydrofluorocarbons (HFCs) l alkanes. These compounds do not contain chlorine atoms, so cannot release chlorine free radicals into the atmosphere. difluoromethane However, both these families of compounds are powerful greenhouse gases. 14 of 51 © Boardworks Ltd 2009

Voting activity: replacing CFCs 15 of 51 © Boardworks Ltd 2009

CFC, alkane or HFC? 16 of 51 © Boardworks Ltd 2009

CFCs: true or false 17 of 51 © Boardworks Ltd 2009

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What are alcohols? Alcohols are a family of organic compounds that contain carbon, hydrogen and oxygen atoms. The defining feature of an alcohol is the –OH group. For example: methanol CH 3 OH 19 of 51 ethanol C 2 H 5 OH propan-1 -ol C 3 H 7 OH © Boardworks Ltd 2009

Boiling points of alcohols 20 of 51 © Boardworks Ltd 2009

Boiling points of alcohols All molecules are held together by intermolecular forces. methanol boiling These forces must be overcome in order for a substance to turn into a gas (boil). The intermolecular forces between alcohol molecules are relatively strong because the –OH groups attract each other. Greater amounts of energy are needed to separate the molecules. This means that alcohols have relatively high boiling points compared to alkanes of the same length. 21 of 51 © Boardworks Ltd 2009

Boiling points: Alcohols vs. alkanes Boiling points are higher for larger alcohol molecules. All molecules are weakly attracted to each other. This attraction is stronger between larger molecules than smaller ones, so boiling points are usually higher. pentan-1 -ol: b. p. = 138°C methanol: b. p. = 65°C This is true of alkanes as well as alcohols – the longer the carbon chain, the higher the boiling point. 22 of 51 © Boardworks Ltd 2009

Investigating boiling points of alcohols 23 of 51 © Boardworks Ltd 2009

Reactivity of alcohols 24 of 51 © Boardworks Ltd 2009

Reaction of alcohols with oxygen Because alcohols contain hydrocarbon chains, they often react in a similar way to alkanes. For example, ethanol burns in oxygen to form carbon dioxide and water: ethanol + oxygen carbon dioxide + water C 2 H 5 OH + 3 O 2 2 CO 2 + 3 H 2 O What is the equation for the reaction of hexane with oxygen? hexane + oxygen carbon dioxide + water 2 C 6 H 14 + 19 O 2 12 CO 2 + 14 H 2 O 25 of 51 © Boardworks Ltd 2009

Reactions of alcohols and water Because alcohols contain an –OH functional group, they often react in a similar way to water. For example, ethanol reacts with sodium to form sodium ethoxide and hydrogen: ethanol + sodium 2 C 2 H 5 OH + 2 Na sodium ethoxide + hydrogen 2 C 2 H 5 ONa + H 2 What is the equation for the reaction of water with sodium? water + sodium 2 H 2 O + 2 Na 26 of 51 sodium hydroxide + hydrogen 2 Na. OH + H 2 © Boardworks Ltd 2009

Alcohols: true or false 27 of 51 © Boardworks Ltd 2009

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Making ethanol Ethanol is used as a fuel, a solvent, and as a feedstock in other reactions. It as also found in alcoholic beverages like beer and whiskey. Ethanol can be made by three methods: l fermentation l hydration of ethene l bacterial action on wood and plant waste. Each of these methods has advantages and disadvantages. 29 of 51 © Boardworks Ltd 2009

Making ethanol by fermentation Most ethanol is made from glucose (sugar) by fermentation: glucose ethanol + carbon dioxide C 6 H 12 O 6 2 C 2 H 5 OH + 2 CO 2 The reaction is performed by yeast. Yeast is a type of fungus. It produces alcohol when it respires anaerobically. This means respiring without oxygen. The yeast metabolizes the sugar to make ethanol and carbon dioxide. The ethanol produced in the reaction is removed from the mixture by distillation. 30 of 51 © Boardworks Ltd 2009

Making ethanol by fermentation 31 of 51 © Boardworks Ltd 2009

Conditions for fermentation – temperature Temperature: A temperature range of between 25 °C and 50 °C is needed for fermentation to be successful. What happens to the rate of reaction at temperatures above and below this range? l If the temperature is too low, the reaction will take place very slowly as the yeast is less active. l If the temperature is too high, the yeast cells are damaged and eventually killed, bringing the reaction to an end. 32 of 51 © Boardworks Ltd 2009

Conditions for fermentation – oxygen Oxygen: If oxygen is present in the mixture, the yeast will respire aerobically, creating only water and carbon dioxide. The presence of oxygen will also oxidize any ethanol that is made, to form ethanoic acid. Under some circumstances this reaction can be useful, for example, in turning wine into vinegar. 33 of 51 © Boardworks Ltd 2009

Conditions for fermentation 34 of 51 © Boardworks Ltd 2009

Making ethanol from ethene Ethanol can also be made by reacting ethene with water. Ethene is mixed with high pressure steam in the presence of a phosphoric acid catalyst: C 2 H 4 + H 2 O phosphoric acid catalyst CH 3 CH 2 OH Most of the ethanol used as feedstock in the petrochemical industry is made using this process, as the reaction is quicker and the product is purer. However, ethene can be expensive as it comes from crude oil. High temperatures and pressures are also needed. 35 of 51 © Boardworks Ltd 2009

Making ethanol from ethene 36 of 51 © Boardworks Ltd 2009

Making ethanol using bacteria Scientists are working on new ways of producing ethanol. Bacteria have been genetically to ferment plant cellulose. Cellulose is a complex carbohydrate found in the tough, rigid parts of plants. Good sources of cellulose include wood, paper, grass cutting and wood chippings. Cellulose comes from the parts of plants which are inedible. It is found in many materials that are usually thrown away. At present however, fermenting cellulose using bacteria is a slow and expensive process. 37 of 51 © Boardworks Ltd 2009

Making ethanol: comparing methods 38 of 51 © Boardworks Ltd 2009

Which method: you decide 39 of 51 © Boardworks Ltd 2009

Using ethanol and methanol Ethanol is the alcohol that is used to make alcoholic drinks. It also has antibiotic properties, so is often used in antibacterial hand wipes. Methanol is used in antifreeze – a liquid that stops car engines from freezing in winter. Methanol and ethanol are widely used for making other chemicals. Both are often used as solvents, to dissolve other chemicals, e. g. in paints and makeup. 41 of 51 © Boardworks Ltd 2009

Using ethanol as a fuel Bioethanol is an alcohol produced by the natural fermentation of the carbohydrates in sugar beet, sugar cane or wheat crops. ‘Flexi-Fuel’ vehicles, fitted with modified fuel injection systems, can run on E 85 fuel (85% bioethanol, 15% petrol), which cuts carbon dioxide emissions by 70% compared to normal petrol-engine cars. What are the advantages and disadvantages of using bioethanol as a fuel, rather than petrol? 42 of 51 © Boardworks Ltd 2009

Using alcohols to make esters Esters are a group of chemicals used as perfumes and flavourings. They contain an –COO– functional group: Esters are made from the reaction of an alcohol with a carboxylic acid: carboxylic acid + alcohol ester + water + methanol methyl + propanoate water For example: propanoic acid 43 of 51 © Boardworks Ltd 2009

Making esters 44 of 51 © Boardworks Ltd 2009

Using ethanol to make ethene 45 of 51 © Boardworks Ltd 2009

Using ethanol to make ethene The reaction that produces ethene from ethanol is called a dehydration reaction, because a molecule of water is removed from each molecule of ethanol ethene + water CH 3 CH 2 OH C 2 H 4 + H 2 O + The reaction needs a high temperature and a catalyst, such as aluminium oxide to work. Making ethene on an industrial scale also requires a high pressure. Why are each of these conditions needed? 46 of 51 © Boardworks Ltd 2009