Acknowledgement. Copyright is held by Peter & Lesley Johnson ( P & L Johnson 2013.)

Transcription

1 P& L Johnson

2 Acknowledgement The Shopping Trolley hemistry workbook and activities were developed and written by Peter Johnson, with the help of Graeme Mitchell and harlie Kerr of the Stewart s Melville ollege hemistry Department. opyright is held by Peter & Lesley Johnson ( P & L Johnson 2013.) This material may only be copied within the purchasing establishment and shall not be loaned, copied or passed onto any third party without the written consent of Peter Johnson. The copyright to any changes or adaptations made to the material will remain with Peter Johnson and as such any adapted form of the material shall not be loaned, copied or passed onto any third party without the written consent of Peter Johnson. P& L Johnson

3 hemistry is everywhere around us and non more so than in your local supermarket! Every time you fill your shopping trolley you are in fact filling it with a huge range of chemicals; including the food we eat; the alcoholic beverages we drink; the soaps and detergents we use to clean; the perfumes we use to smell nice and the skincare we use to beat the aging process. This unit will take us through the important areas of food, drink, detergents, perfumes and skincare products and show how an understanding of the chemistry behind these everyday items can help us make informed decisions and choices. This is particularly important given the extensive use of Science to sell and market products to us. 2a Booze Alcoholic hemistry Page 5 2b Food Kitchen hemistry Page 15 2c Detergents lean hemistry Page 26 2d Fragrances Smelly hemistry Page 28 2e Skincare Ageless hemistry Page 30 P& L Johnson

4 By the end of this unit you should know the following: ow ethanol is produced both by fermentation and hydration of ethene. ow the hydroxyl functional group effects its properties and uses. You should also be able to name and draw a variety of different alcohols. That carboxylic acids contain the carboxyl functional group and how this effects the properties and uses of these compounds. You should also be able to name and draw a variety of different carboxylic acids. Esters are formed by the reversible reaction of alcohols and carboxylic acids. They are responsible for many fruit flavours but are also used in a variety of other ways as solvents or plastics. The hydrolysis of esters causes the formation of the original alcohol and carboxylic acid. Fats and oils are a concentrated source of energy and are essential for the transport and storage of fat soluble vitamins in the body. The degree of unsaturation in the molecule affects its melting point and this determines whether it is a fat or oil. Proteins have many important functions within living organisms. They are formed by the joining together of thousands of amino acid molecules by peptide links. The hydrolysis of proteins results in the formation of various amino acids. ooking food has many effects on the flavour and texture of food. Flavour molecules can be water soluble or oil soluble depending on their structure. Proteins can change shape when heated and this affects the texture of foods. xidation can also affect food and drinks and antioxidants can be useful in preventing this. Soaps can be made from the hydrolysis of fats and oils resulting in a long fat-liking chain with a water-liking head. This structure allows the soap to dissolve dirt and oil and help clean clothes and dishes. Emulsions occur when droplets of one liquid are dispersed in another liquid and are important in cooking. Fragrances are often made with essential oils extracted from plant material, they often contain terpenes which are responsible for many distinctive aromas. Ultra violet light is responsible for sunburn and other skin aging effects, sunscreens contain chemicals that either reflect the UV light or absorb it preventing damage to the skin. Ultra violet light can also cause molecules to turn into free radicals which are highly reactive molecules or atoms that react in a series of steps called initiation, propagation and termination. Many consumer products contain free radical scavengers to prevent these reactions occurring. P& L Johnson

5 Alcoholic Drinks There are a wide range of drinks that contain alcohol including wine, spirits, beer and alcopops. They are all made using the fermentation of a carbohydrate, whether it be grapes for wine, barley for beer and whiskey or even rice and potatoes for sake and vodka. ATIVITY 2.1: Fermentation Your teacher may demonstrate or allow you to make some alcohol using fermentation. In order for fermentation to occur yeast is used which contains an enzyme, zymase. The process must be carried out in warm conditions but not above 50 o. Even in optimum conditions the percentage of alcohol is only 15%. In order to produce alcoholic drinks with an alcohol percentage greater than 15%, distillation is used. After discussion with your teacher and others make sure you can explain how fermentation is used to produce alcohol. With the help of a labelled diagram explain how alcohol is made by fermentation. opy and complete the table below: Alcoholic drink Beer Wine Whiskey Vodka Sake ider Gin P& L Johnson Source of carbohydrate

6 ATIVITY 2.2: Distillation Your teacher may demonstrate or allow you to produce some pure alcohol using distillation. After discussion with your teacher and others make sure you can explain how distillation is used to produce pure alcohol, including the temperature used. With the help of a labelled diagram explain how you produce pure alcohol by distillation. ALL INVESTIGATIN : Your teacher may get you to take part in an extended investigation on the topic of alcohol. Alcohol Awareness ATIVITY 2.3: Your teacher may discuss and run some activities with you on the problems of drinking too much alcohol. After discussion with your teacher and others can you identify some of the problems associated with binge drinking. Produce an information booklet on the problems associated with binge drinking. P& L Johnson

7 Industrial Alcohol To meet market demand, ethanol can be made by methods other than fermentation. ne industrial method involves the addition of water to ethene using concentrated phosphoric acid as a catalyst. This kind of reaction is called catalytic hydration. Further processing of the ethanol removes any traces of water and creates a product that is much purer than alcohol produced by normal fermentation and distillation. Alcohol with this higher purity is often used by the pharmaceutical and cosmetics industry. + ATIVITY 2.4: recreate the reaction. If you have Molymod kits your teacher may get you to After discussion with your teacher and others make sure you can explain how the catalytic hydration of ethene works and why this method is used instead of fermentation. Use full structural formulae to show the catalytic hydration of ethene and explain why this method is used instead of fermentation. Uses of alcohols Due to the presence of the hydroxyl group (-) alcohols are polar molecules. The shorter the chain of carbon atoms the more polar the molecule. The polarity of the alcohols makes them good polar solvents and due to their ease of evaporation they find uses in many pharmaceutical and cosmetic preparations. As a hydrocarbon containing oxygen they burn cleanly and ethanol and methanol can both be used as fuels in cars. ATIVITY 2.5: Design and carry out an experiment that could demonstrate that the polarity of alcohols reduces as the carbon chain gets longer. ATIVITY 2.6: Your teacher may demonstrate the flammability of ethanol. Then you can design an experiment to decide which is the best fuel between ethanol and methanol. P& L Johnson

8 Alcohols The alcohol found in alcoholic drinks is called ethanol. There are many types of alcohol with different structures and uses, but all have the same feature or functional group called a hydroxyl group. A hydroxyl group consists of an oxygen and hydrogen (-) attached to the carbon chain. If the alcohol is a straight chain alkane with a hydroxyl group along the chain it is a member of the alkanol homologous series. ATIVITY 2.7: If you have Molymod kits your teacher may get you to make the first four members of the alkanol homologous series. After discussion with your teacher and others make sure you can work out the correct chemical and structural formula for the first four members of the alkanol homologous series. Show what functional group an alcohol contains and what the members of the alkanol homologous series look like by copying and completing the following table. Name hemical Formula Shortened structural formula Full structural formula methanol ethanol propanol butanol P& L Johnson

9 Systematic Naming This can be used to name branched chain hydrocarbons containing the hydroxyl functional group: Identify the longest chain of carbon atoms. (4 = but) 2. Number the carbon atoms starting at the end carbon nearest the functional group or branch if there is no functional group. (right hand side) 3. Identify the type and position of any functional groups. (hydroxyl, carbon 2) 4. Identify the type and position of any branches. (2 x methyl, carbon 3 & 3) 5. Put together in the following format; position of, number of and type of branches, then the number of carbons in the longest chain and then the position of and type of functional group. e.g. 3,3-dimethylbutan-2-ol After discussion with your teacher and others make sure you can work out the correct systematic name of a variety of alkanols. Using the above example show how the systematic name of an alkanol can be derived from its structural formula. Quick Test 1 1. Draw the full structural formula of 3-methyl butan-2-ol 2. Draw the full structural formula of 2,3-dimethyl pentan-1-ol 3. Name the following alcohols: ( 3 )( 3 ) 3 P& L Johnson

10 arboxylic Acids If you have ever tasted an alcoholic drink, like wine, that has been left in a glass overnight, you will know that it can taste horrible and vinegary. This is because the wine has been oxidised. Vinegar that you use in cooking is made by speeding up this oxidation process, red wine, white wine and cider can all be used to make vinegar. Vinegar s chemical name is ethanoic acid, sometimes called acetic acid. It is a member of a group of compounds called carboxylic acids, which contain the carboxyl functional group (-). If it is a straight chain hydrocarbon containing the carboxyl functional group it is known as an alkanoic acid. ATIVITY 2.8: If you have Molymod kits your teacher may get you to make the first four members of the alkanoic acid homologous series. After discussion with your teacher and others make sure you can work out the correct chemical and structural formula for the first four members of the alkanoic acid homologous series. Show what functional group a carboxylic acid contains and what the members of the alkanoic acid homologous series look like by copying and completing the following table. Name hemical Formula Shortened structural formula Full structural formula methanoic acid ethanoic acid propanoic acid butanoic acid P& L Johnson

11 ATIVITY 2.9: Testing carboxylic acids Your teacher will give you a selection of carboxylic acids to test for smell, p and reactivity. After discussion with your teacher and others can you identify any trends in smell, p and reactivity as the length of the carbon chain in the carboxylic acid increases. After completing the experiments copy and complete the following table and note any trends in smell, p and reactivity as the length of the carbon chain increases. Name Smell p Reaction with magnesium methanoic acid ethanoic acid propanoic acid Naming Branched arboxylic Acids In the same way that branched alcohols can be named systematically, so can branched carboxylic acids. The same process is used except the ending will always be the name of the main chain alkanoic acid, with carbon number 1 being the carbon in the carboxyl functional group. 3 E.g ,3-dimethylbutanoic acid Reactions of arboxylic Acids arboxylic acids are formed by oxidation reactions and so can be converted back to aldehydes and alcohols by a reduction reaction using lithium aluminium hydride, LiAl 4. P& L Johnson

12 ATIVITY 2.10: Neutralisation of carboxylic acids Neutralise ethanoic acid using sodium hydroxide, using p paper to check it is no longer acidic. Evaporate off the water to leave the salt, sodium ethanoate. After discussion with your teacher and others can you work out chemical equations for the formation of salts from the neutralisation of different carboxylic acids using a variety of bases. Write a brief note on the formation of salts from carboxylic acids. Fruit Flavours You may be familiar with fruit flavoured drinks called alcopops here fruit flavours are added to a base alcohol such as vodka, rum or beer. They tend to be sweet and there is some concern that they appeal to underage drinkers and encourage binge drinking. The fruit flavouring may be natural or synthetic, but in both cases they contain a group of compounds called esters. ATIVITY 2.11: Identifying Esters Your teacher will give you a selection of esters to smell. Use the labels on the bottle to find the name and formula of the ester, then try and think where you have smelt it before. After discussion with your teacher and others can you recognise the smells of some common esters and what they are used for. After completing the experiment copy and complete the table below: Name of ester hemical Formula Where have you smelt it before? P& L Johnson

13 Naming and Drawing Esters Esters are compounds that contain an ester link (--) or (--). They are made by reacting an alcohol with a carboxylic acid; with the parent alcohol and carboxylic acid forming the name of the ester. Methanol and methanoic acid react together to form the ester methyl methanoate. methanol + methanoic acid methyl methanoate + water The name of the ester is made up of two parts the alcohol (alkyl) part and the carboxylic acid (alkanoate) part. Ester link ethyl propanoate made by reacting ethanol with propanoic acid ATIVITY 2.12: Your teacher may let you play the Ester card game. After discussion with your teacher and others can you draw and name esters correctly? an you work out the name and structure of an ester by looking at the parent alcohol and carboxylic acid? opy the above examples into your notes, explaining how to name esters both from their structure and their parent alcohol and carboxylic acid. P& L Johnson

14 Making Esters In order for the alcohol and carboxylic acid to react, they need to be gently heated in the presence of an acid catalyst. ATIVITY 2.13 : Making esters Using a variety of alcohols and carboxylic acids, a wide range of esters can be produced. 1. Add an alcohol to a test tube to a depth of 1cm. 2. Add to this the same volume of a carboxylic acid. 3. arefully smell the mixture by wafting. 4. Get your teacher to add 5 drops of concentrated sulfuric acid to the mixture. 5. Wrap a piece of wet tissue paper around the neck of the test tube and hold it in place with an elastic band. Then place a loose plug of cotton wool in the neck of the tube. As shown. 6. Place the test tube in a hot water bath for about 30 minutes. Wet paper towel condenser Water bath Alcohol, carboxylic acid and concentrated sulfuric acid 7. Remove the plug of cotton wool and pour the contents of the tube in to a beaker containing 50cm 3 of sodium carbonate solution, to neutralise the acid catalyst. 8. Look at the surface of the solution for an oily layer and gently waft to smell if you have produced an ester. After discussion with your teacher and others can you describe the experimental procedure for making an ester, including the purpose of the concentrated sulfuric acid, the wet paper towel condenser and the water bath. opy the above diagram and then explain the purpose of the concentrated sulfuric acid; the wet paper condenser and the water bath. Using full structural formula show how your chosen alcohol and carboxylic acid formed the ester and name it. P& L Johnson

15 Uses of Esters Ester are used in a wide range of applications including food flavourings, solvents and plastics. ATIVITY 2.14: Using a variety of sources, including consumer packaging, identify three different uses of esters: ATIVITY 2.15: ethanoate Solvent extraction of caffeine from tea using ethyl Your teacher may demonstrate or allow you to calculate the mass of caffeine in tea. After discussion with your teacher and others can you identify different uses of esters. After completing the above activities copy and complete the table below: Ester Formula Use ydrolysis of Esters Esterification reactions are reversible and so an ester can be broken back into its original alcohol and carboxylic acid by hydrolysis, usually using aqueous sodium hydroxide solution. ATIVITY 2.16 : Your teacher may demonstrate the hydrolysis of an ester, showing that an alcohol and carboxylic acid are formed. methyl ethanoate methanol + ethanoic acid + P& L Johnson

16 After discussion with your teacher and others can you describe the experimental procedure for hydrolysing an ester and work out the products for the reaction. Describe the experimental technique for the hydrolysis of an ester and show with structural formulae the reaction. 1. Which of the following is an ester? Quick Test 2 2. Rum flavouring is based on the compound with the formula shown: It can be made from A. ethanol and butanoic acid B. propanol and ethanoic acid. butanol and methanoic acid D. propanol and propanoic acid.. 3a. Give the systematic names of the two compounds which, when warmed with concentrated sulfuric acid, react to form the compound below. b. Give the name and draw the structural formula of the organic product formed by heating pentan-1-ol and propanoic acid with concentrated sulfuric acid. P& L Johnson

17 Food Groups In order to be healthy it is important that we eat a balanced diet. This includes carbohydrates, fats & oils, proteins, vitamins, minerals, fibre and water. ATIVITY 2.17: Using a variety of sources, including consumer packaging, identify the recommended proportions of food sources for a balanced healthy diet: After discussion with your teacher and others can you describe what a balanced healthy diet is, giving examples of the types of food that contain good sources of carbohydrates, fats & oils, proteins, vitamins, minerals and fibre. opy and complete the following table in to your notes and give examples of the types of food that contain good sources of carbohydrates, fats & oils, proteins, vitamins, minerals and fibre. Food Source % of daily intake Fruit & vegetables Bread, rice, potatoes and pasta Meat, fish, eggs and beans Milk and dairy foods Foods high in fat and sugar ATIVITY 2.18: onstruct a food diary and track your own intake of these food sources for a week. Try to estimate what percentage of your diet is made up of the food sources shown above. P& L Johnson

18 Fats & ils Fats and oils are an essential part of our diet, as they are a more concentrated source of energy compared to carbohydrates and provide essential fatty acids. They are also necessary in order to transport and store fat soluble vitamins. Fats and oils are a very good source of energy. There are three sources of fats and oils; plant, animal and marine. ATIVITY 2.19: Look at a selection of fats and oils from vegetable, animal and marine sources. After discussion with your teacher and others can you explain why fats and oils are an important part of a healthy diet and also give examples of three different sources of fats and oils. opy and complete the following table in to your notes of examples of fats and oils and their source. Explain why fats & oils are an essential part of any healthy diet. Example of Fat or il Lard od-liver il live il Source of Fat or il Animal Marine Plant ATIVITY 2.20: pan fire! Your teacher may demonstrate the dangers of a chip After discussion with your teacher and others can you describe how to put out a chip pan fire safely. Describe how you would safely put out a chip pan fire. P& L Johnson

19 The structure Fats and oils are esters formed from the condensation of glycerol (propane-1,2,3 -triol) and three carboxylic acid molecules, known as fatty acids. Ester links The carboxylic acids are known as "fatty acids" and are saturated or unsaturated straight chain carboxylic acids, usually with long chains of carbon atoms. The following structures show two fatty acids where the carbons atoms in the chain and their hydrogen's are not shown for ease of drawing. Palmitic acid (saturated fatty acid) Linoleic acid (unsaturated fatty acid) It is the level of unsaturation in the fatty acid chains that determines whether the molecule is a solid or liquid at room temperature and hence whether it is termed a fat or oil. The saturated chains in a fat are able to pack closer together and therefore have stronger Van der Waal forces of attraction between the chains causing the melting point to be higher. This is what makes fats solid at room temperature. ATIVITY 2.21: Your teacher may demonstrate or get you to work out the different degree of unsaturation in various fats and oils. After discussion with your teacher and others can you describe the structure of a fat or oil and show that the difference in melting point for fats and oils is due to the difference in their degree of unsaturation. opy the above example of the general structure of a fat or oil explaining how it forms from a glycerol molecule and three fatty acids. Then with the aid of a diagram explain the difference in melting points of fats and oils with regards to their ability to pack next to one another. P& L Johnson

20 Proteins The diagram below shows some of the important functions proteins carry out. arrying oxygen Enzymes Growth & Repair ormones Proteins Antibodies & white blood cells Building & controlling muscles Amino Acids Proteins are natural polymers made by joining together amino acid molecules. All amino acid molecules contain a central carbon atom with an amine and carboxyl functional group, they differ by the nature of the side group R, which can range from a single atom to much more complicated groups. Glutamic acid There are 22 different amino acids but some cannot be synthesised in the human body and must therefore be consumed in our diets. ATIVITY 2.22: After discussion with your teacher and others identify the structure of the essential amino acids and if you have access to molymod kits you could make a number of these. Glycine After discussion with your teacher and others can you describe the many functions that proteins carry out in the human body and identify the main features of the amino acid structure. Write a note on the importance of proteins in our diet and give examples of the type of functions they carry out in the human body. Then draw the general structure of an amino acid and the two examples shown above. P& L Johnson

21 Peptide Links Proteins are made of many amino acid molecules linked together by condensation reactions. In these condensation reactions, the amino group on one amino acid and the carboxyl group on a neighbouring amino acid join together, with the elimination of water. The link which forms between the two amino acids can be recognised as an amide link (-N-). Proteins which fulfil different roles in the body are formed by linking differing sequences of amino acids together. The amide links within proteins are also known as peptide links. Below is an example of three different amino acids forming part of a protein chain: peptide links ATIVITY 2.23: If you have made molymod models of some essential amino acids you could join them together to form a section of protein. There are two types of protein structure globular and fibrous. Globular proteins form complex shapes, with the chain coiled around itself, held in position by weak forces of attraction such as hydrogen bonding. Globular proteins are often water soluble. Fibrous proteins are made of long straight chains tightly packed together forming solid structures that are insoluble. After discussion with your teacher and others can you explain how amino acids join together with peptide links to form long protein chains and describe the two types of protein structure and give examples of these in the human body. opy the above diagram into your notes and use it to explain how protein chains form. Then describe how the two types of protein structure occur and how their structure affects the properties and uses in the human body. opy and complete the table below. Protein Structure Examples found in the human body Globular Fibrous P& L Johnson

22 ydrolysis of Proteins During digestion our bodies break down the protein chains into their constituent amino acids using a process called hydrolysis. Enzymes are used in the body to do this but you can use acids or alkalis to do it in the laboratory. The mixture of amino acids can then be separated and identified using paper chromatography. ATIVITY 2.24: Analysis of hydrolysed protein using paper chromatography. Your teacher may show you or discuss how you would set up a chromatogram to identify the amino acids present in a sample of hydrolysed protein A piece of chromatography paper is spotted with the hydrolysed protein mixture and the five reference amino acids. The paper is dried then placed in a chromatography tank and a little solvent allowed to rise up the paper. The paper is dried then sprayed with Ninhydrin, in a fume cupboard and allowed to dry. The purple spots show where the amino acids have risen to. 1. ydrolysed protein, 2. Lysine, 3. Glycine, 4. Aspartame, 5. istidine, 6. Tyrosine After discussion with your teacher and others can you explain how proteins are hydrolysed and how the resulting amino acids can be identified using paper chromatography. opy the above reaction sequence into your notes and use it to explain how our bodies hydrolyse proteins. Describe how paper chromatography can be used to identify the amino acids present in a sample of hydrolysed protein. P& L Johnson

23 Quick Test 3 1. Fats and oils can be classified as A acids B carbohydrates alcohols D esters. 2. Glycerol can be obtained from fats and oils by A condensation B hydrolysis oxidation D hydrogenation. 3. The breakdown of fats and oils produces glycerol and fatty acids in the ratio of A one to one B three to one one to three D one to four. 4. Which compound can be made by the breakdown of some proteins A leic acid B Glucose Glycerol D Glycine (amino ethanoic acid) 5. Proteins can be made from amino acids by which reaction? A ydrolysis B ydration ondensation D ydrogenation 6. When proteins like enzymes are denatured, the protein molecule A is polymerised B is killed is neutralised D changes shape. P& L Johnson

24 Flavour The flavour of food is mainly due to volatile molecules that are detected by our nose when we eat the food. Flavour molecules tend to be small molecules with low boiling points. Some flavour molecules are more soluble in water than oil and vice-versa. Limonene (ranges) Prop-2-enyl hexanoate (pineapple) Furaneol (strawberry) After discussion with your teacher and others can you explain, with reference to the bonding involved, why flavour molecules are volatile. Also can you suggest a reason why the furaneol molecule is water soluble while the limonene molecule is oil soluble. opy the structural formulae of both limonene and furaneol into your notes and then explain with reference to their bonding why they are both volatile but limonene only dissolves in oil whereas furaneol readily dissolves in water. ATIVITY 2.25: Flavour Testing Activity. Your teacher may allow you to taste different foods with your nose blocked to see if you can identify them. Then unblock your nose to get the true taste. P& L Johnson

25 Effect of ooking Food Within proteins, the long chain molecules may be twisted to form spirals, folded into sheets, or wound around to form other complex shapes. The chains are held in these forms by intermolecular bonding between the side chains of the constituent amino acids. When proteins are heated, during cooking, these intermolecular bonds are broken allowing the proteins to change shape (denature). These changes alter the texture of foods. ATIVITY 2.26: Effect of heat on egg whites Your teacher may show you how the protein structure changes when an egg is cooked. After discussion with your teacher and others can you explain how proteins are denatured and the effect this has on the texture of foods. Use the above diagram of a section of a globular protein to explain how cooking changes the shapes of protein structures and how this affects the texture of food. xidation of Food & Drinks Alcohols can be classed as either primary, secondary or tertiary depending upon where in the structure the hydroxyl functional group is. If the hydroxyl group is attached to an end carbon it is a primary alcohol; if the hydroxyl group is attached to a carbon atom in the middle of a straight chain it is a secondary alcohol and if the hydroxyl group is attached to a carbon atom in the middle of a branched chain it is a tertiary alcohol: 3 Primary Secondary Tertiary Butan-1-ol Butan-2-ol 2-methyl propan-2-ol P& L Johnson

26 After discussion with your teacher and others can you explain how alcohols can be classed as primary, secondary or tertiary, depending on where in the chain the hydroxyl group is attached. opy the three structures on the previous page into your notes and use them to explain how alcohols are classed as primary, secondary or tertiary depending on where the hydroxyl functional group is attached. Quick Test 4 1. Decide whether the following molecules will be oil soluble or water soluble: a. b. c. 2. Decide whether the following alcohols are primary, secondary or tertiary: a. b. c. 3 Vanillin cyclohexyne ATIVITY 2.27: xidation of alcohols using acidified potassium dichromate After completing the experiment copy and complete the table below: Aspirin (acetylsalicylic acid) Name of alcohol Primary, Secondary or Tertiary Effect on acidified potassium dichromate P& L Johnson

27 When an alcohol is partially oxidised the hydroxyl functional group is changed into a carbonyl group. Primary alcohols form an aldehyde, in the case of a secondary alcohol a ketone is formed. In both cases the oxygen to hydrogen ratio is increased. Tertiary alcohols cannot undergo partial oxidation. Butan-1-ol Butanal Butan-2-ol 3 Butanone 2-methyl butan-2-ol opy the structural equations above and use them to explain how alcohols can be oxidised into aldehydes and ketones. ATIVITY 2.28: xidation of ethanol using a copper coin Your teacher may demonstrate how to oxidise ethanol using a red hot copper coin. After discussion with your teacher and others can you explain the colour changes taking place on the coin and the change in smell that occurred during the experiment. Using full structural formula explain the change to the ethanol that occurred during the experiment and what compound caused the change. P& L Johnson

28 Naming Aldehydes & Ketones There are many types of carbonyls with different structures and uses, but all have the same feature or functional group. A carbonyl group consists of an oxygen attached to the carbon chain with a double bond (=). If the carbonyl is at the end of the chain it is an aldehyde, if the carbonyl is anywhere else along the chain it is a ketone. If the carbon chains are alkanes then the aldehyde and ketones become members of the alkanal and alkanone homologous series respectively. ATIVITY 2.29: If you have Molymod kits your teacher may get you to make some of the first four members of the alkanal & alkanone homologous series. After discussion with your teacher and others make sure you can work out the correct chemical and structural formula for the first four members of the alkanal & alkanone homologous series. Show what functional group an alkanal & alkanone contains and what the members of the alkanal & alkanone homologous series look like by copying and completing the following table: name Shortened structural formula Full structural formula methanal ethanal propanone butanone P& L Johnson

29 Further xidation Aldehydes can undergo further oxidation using the same oxidising agents as before i.e. hot copper oxide or acidified potassium dichromate. You can also use Tollen s reagent or Benedicts (Fehlings) reagent; ketones cannot react and therefore this reaction can act as a test for aldehydes or ketones. propanal propanoic acid propanone ATIVITY 2.30: Testing for Aldehydes and Ketones Experiment with a known ketone and aldehyde using Tollen s reagent and Benedict s reagent and then use your findings to help identify two unknown compounds. After discussion with your teacher and others can you changes that occurred during the experiments. explain the colour opy the structural equations above and use them to explain how aldehydes and ketones can be identified by a chemical test; giving the results of a positive test for an aldehyde. P& L Johnson

30 Antioxidants xygen reacts with edible oils giving the food a rancid flavour. Antioxidants are molecules which will prevent these oxidation reactions taking place. They do this by being oxidized themselves, so antioxidants are often good reducing agents. Vitamin is also called ascorbic acid and is thought to act as an antioxidant in the body. Ascorbic acid is a good reducing agent as it is readily oxidised itself: e - ATIVITY 2.31: Brown Apples Your teacher may get you to set up an experiment to find which fruit juice is best at preventing apples from going brown, a process caused by oxidation. Many fruits, vegetables and teas contain antioxidants and are believed by many to have beneficial health effects. IGER INVESTIGATIN ANTIXIDANTS Your teacher may get you to complete an investigation on antioxidants. Quick Test 5 1. Draw the full structural formula for the following: a. ethanol b. propanone c. pentanal d. hexan-3-one 2. Draw the following carboxylic acids then identify the parent alkanal from which they were formed: a. pentanoic acid b. methanoic acid c. hexanoic acid 3. Name the following molecules: 3 3 a. b. c P& L Johnson

31 Making Detergents Soaps are produced by the alkaline hydrolysis of fats and oils. Fats and oils are esters. The hydrolysis of fats and oils produces fatty acids and glycerol in the ratio of three moles of fatty acid to one mole of glycerol. The fatty acid molecules released are neutralised by the alkali to form water soluble ionic salts called soaps. ATIVITY 2.32: Making Soap Your teacher may get you to make soap from an oil and sodium hydroxide. oil liking tail water liking head Soap ions have a long non-polar tail, readily soluble in non-polar compounds (hydrophobic) such as grease, and an ionic carboxylate head which is water soluble (hydrophilic). After discussion with your teacher and others can you explain how soaps are made and what their structure is. opy the structural equations above and use them to explain how soaps are formed and what their structure looks like. P& L Johnson

32 leansing Action of Soaps leaning with water alone has little effect when stains consist of non-polar substances, such as grease and sweat. The structure of soaps allow fats and oils to break away from the fabric and disperse in water. During cleaning, the hydrophobic tails dissolve in a droplet of oil or grease, whilst the hydrophilic heads face out into the surrounding water resulting in ball-like structure. With agitation or scrubbing the grease becomes dislodged from the surface and further soap ions attach themselves. The non-polar substances, such as oil and grease, are held inside the ball and suspended in the water. soap molecules water oil or grease After discussion with your teacher and others can you explain how soaps work? opy the diagram above and use it to explain how soaps help remove grease from dirty dishes and clothes. Emulsions An emulsion contains small droplets of one liquid dispersed in another liquid. Emulsions in food are mixtures of oil and water. Examples of emulsions are mayonnaise and milk which have fat or oil droplets suspended in water and butter and margarine which have water droplets suspended in fat. To prevent oil and water components separating into layers, a soap-like molecule known as an emulsifier is added. The emulsifier acts in a similar way to a soap. After discussion with your teacher and others can you explain what an emulsion is? Giving some examples, explain what an emulsion is. E m u l s i o n structure of m a y o n n a i s e viewed using m i c r o s c o p e with 1000 magnification. il bubbles are tr a pped i n water. P& L Johnson

33 Emulsifiers for use in food are commonly made by reacting edible oils with glycerol to form molecules in which either one or two fatty acid groups are linked to a glycerol backbone rather than the three normally found in edible oils. The one or two hydroxyl groups present in these molecules are hydrophilic whilst the fatty acid chains are hydrophobic. The emulsifying agent can therefore act like a soap and allow the oil, for example, to disperse in small droplets throughout the water. oil water Shake Settle Emulsifying agent Shake & Settle ATIVITY 2.33: Testing Emulsifying Agents Design an experiment that shows which is the best emulsifying agent out of those supplied. After discussion with your teacher and others can you explain how an emulsifying agent works and how you can test the effectiveness of different emulsifying agents? opy the diagram above and use it to explain how emulsifying agents help oil and water to mix. Then describe your experiment that allowed you to identify the best emulsifying agents. opy and complete the following table: Agent Effect P& L Johnson

34 Essential ils Essential oils are concentrated extracts of the volatile, non-water soluble aroma compounds from plants. They are widely used in perfumes, cosmetic products, cleaning products and as flavourings in foods. Essential oils are mixtures of organic compounds. Terpenes are key components in most essential oils. Tea Tree Leaves ATIVITY 2.34: Steam Distillation to Extract Essential ils Your teacher may show or allow you to use steam distillation to extract essential oils from citrus fruits. After discussion with your teacher and others can you explain how to extract essential oils from citrus fruits. Tea Tree il Draw a diagram of the apparatus used to extract the essential oil and explain how the process works. Terpenes Terpenes are unsaturated compounds formed by joining together isoprene (2- methylbuta-1,3-diene) units. They can join in long chains or form ring structures. They are components in a wide variety of fruit and floral flavours and aromas. 3 Linalool gives coriander leaves their lemony taste. Limonene gives lemons and oranges their distinctive smell. 3 Terpenes can be oxidised within plants producing some of the compounds responsible for the distinctive aroma of spices. They are then called terpenoids and can contain hydroxyl or carbonyl functional groups. oriandrin, responsible for part of the aroma of coriander seeds. P& L Johnson

35 Isoprene units can join in long chains or can form ring structures, as shown below: Isoprene unit 2 2 Myrcene is a component of plants, including bay, ylang-ylang and thyme Limonene is a cyclic terpene found in oranges and lemons. ATIVITY 2.35: If you have Molymod kits your teacher may get you to make some essential oils so you can identify the isoprene units. After discussion with your teacher and others can you identify isoprene units in terpene and terpenoid molecules? Draw the structure of an isoprene unit, then draw an example of both a terpene and terpenoid and highlight the isoprene units that make them up. P& L Johnson

36 Quick Test 6 1. Identify the isoprene units is the following terpne and terpenoid molecules: a. b. c. d. e. P& L Johnson

37 Effect of Sunlight Ultraviolet radiation (UV) is a high -energy form of light, present in sunlight. Exposure to UV light can result in molecules gaining sufficient energy for bonds to be broken. This is the process responsible for sunburn and also contributes to aging of the skin. Sun -block products prevent UV light reaching the skin. The following images show how the UV light is absorbed by the sunscreen and therefore appears darker in ultraviolet light. UV light is responsible for how the o r i g i n a l p h o t o g r a p h s w e r e developed. The first permanent photograph was an image produced in 1826 by the French inventor Joseph Nicéphore Niépce. is photographs were produced on a polished pewter plate covered with bitumen of Judea, which he then dissolved in white petroleum. ver the next few years the discovery that exposure to light caused silver halides to change colour led to a revolution in photographic technique. ATIVITY 2.36: Spy amera hallenge Your teacher may get you create your own photograph in this Mission Impossible hallenge. P& L Johnson

38 Free Radical Action When UV light breaks bonds free radicals are formed. Free radicals have unpaired electrons and, as a result, are highly reactive. Free radical chain reactions include the following steps: initiation, propagation and termination. alogenation of Alkanes Normally a mixture of methane (or any alkane) and chlorine would not react. But under the influence of UV light a reaction takes place. ow? The light causes the chlorine molecules to form radicals thus :- l 2 l + l INITIATIN 1. hlorine radicals react with methane l l Methyl radical 2. Methyl radicals react with chlorine molecules 3 + l 2 3 l + l The chlorine radical has been regenerated and now reacts with another methane molecule. l l and so on many times This is called a AIN REATIN 3. When two radicals collide they form a single unreactive molecule 3 + l 3 l P r o p a g a t i o n l + l l 2 This is called a TERMINATIN REATIN ATIVITY 2.37: Reacting ydrogen and hlorine using UV light Your teacher may demonstrate or show you a video clip of the explosive reaction between hydrogen and chlorine. P& L Johnson

39 After discussion with your teacher and others can you identify some useful and undesirable effects of UV light. an you explain how UV light can cause free radicals to form, react and terminate in the processes of initiation, propagation and termination. Write a note describing both the beneficial and undesirable effects of UV light. opy the examples on the previous page and use them to explain the processes of initiation, propagation and termination. Many cosmetic products contain free radical scavengers; molecules which can react with free radicals to form stable molecules and prevent chain reactions. Free radical scavengers are also added to food products These preservatives include natural antioxidants such as ascorbic acid (AA, E300) and tocopherols (E306), as well as synthetic antioxidants such as propyl gallate (PG, E310), tertiary butylhydroquinone (TBQ), butylated hydroxyanisole (BA, E320) and butylated hydroxytoluene (BT, E321). ATIVITY 2.38: Free Radical Scavengers Look at various food packaging and see if you can identify the free radical scavengers used. After discussion with your teacher and others can you identify some free radical scavengers in beauty products and everyday foods. opy and complete the following table after looking at examples of beauty products and everyday foods: Free Radical Scavenger Product P& L Johnson

40 Quick Test 7 1. B is converted into by a free radical mechanism. Write an equation for (i) the initiation step (ii) one of the propagation steps in this mechanism 2. Which of the following does not apply to the reaction between chlorine and methane? A. Requires UV light B. A chain reaction. Formation of a methane radical D. Formation of a chlorine radical. 3. Which of the following represents a termination step in a chain reaction? A. 4 + l l B. l. + l. l l 2 3 l + l. D. l 2 l. + l. P& L Johnson