Topic 8 – National 5 Chemistry Summary Notes Everyday Consumer Products In this topic you will learn about two new homologous series of compounds called alcohols and carboxylic acids and how they can be used to make an important group of compounds called esters. Alcohols from Carbohydrates LI 1-4 When we talk about alcoholic drinks we really mean drinks containing a particular member of the alcohol family called ethanol. Ethanol is generally made by a process called fermentation. Fermentation is brought about by enzymes in yeast which convert the simple sugar called glucose into ethanol. Glucose is part of a large family of compounds called carbohydrates. Carbohydrates contain the elements carbon, hydrogen and oxygen with a ratio of 2:1, hydrogen:oxygen. As you have learnt about in earlier science topics, plants are a source of carbohydrates and the main carbohydrate found in plants is starch. Starch is the ideal way for plants to store energy. It is insoluble so cannot be washed away but this large, insoluble and complex carbohydrate, is broken down easily by enzymes to form glucose a small, simple sugar molecule which dissolves easily. This type of reaction uses the addition of water to break down large molecules and is called hydrolysis. This same hydrolysis reaction breaks down many compounds in our digestive systems using acid and enzymes so that small soluble molecules can be made and easily passed through the gut wall and on into our cells. Remember!!- Enzymes are biological catalysts used by living things to make reactions go faster. A good example of an enzyme is the catalyst amylase, used to break starch down into simple sugars. Summary of Properties of Starch and Glucose Type of Carbohydrate Formula Solubility Starch Glucose 1 Reaction with Iodine Reaction with Benedict’s LI 5&6 Fermentation Fermentation is big business in Scotland! There are nearly 20,000,000 barrels of whisky sitting maturing in warehouses at any one time all made by fermenting barley. Many different alcoholic drinks are made from different plant sources. They all contain the alcohol called ethanol but have many other flavour molecules to give distinctive drinks: Type of alcoholic drink Whisky Beer Wine Cider Plant source of carbohydrate Barley Alcohol Content (%) We can make ethanol by fermentation in the school laboratory: C6H12O6 2C2H5OH + 2CO2 glucose ethanol + carbon dioxide We can prove we made carbon dioxide by bubbling it through limewater because it will _________________________. How can we prove we have made ethanol? Answer- Ethanol has a lower boiling point than water ( 78⁰C) so we can separate it out by distillation and show that it burns. Ethanol burns very well. (it also smells!!) The maximum % of alcohol we can produce by fermentation is around 14% because the ethanol is a poison and yeast, a living organism, is killed by high levels of ethanol. Distillation has to be used to produce drinks of a higher alcohol content. 2 Enzyme Optimal Conditions Not only do high levels of ethanol stop yeast working, the activity of the enzymes in yeast ( and all enzymes) are easily affected by the conditions they are working in. They are sensitive to changes in temperature and pH and work best within a narrow range of pH and temperature. Each individual enzyme has its own set of ideal conditions called “optimal conditions”. Units of Alcohol As mentioned ethanol is a poison and it is important not to take too much. You will research as a homework how many units of alcohol we should be drinking and what volume of each drink contains one unit of alcohol: Alcoholic Drink Alcohol Content % whisky gin beer vodka wine 3 What volume equals ONE unit (cm3) LI 7 Structure and Functional Group of Alcohols Ethanol is the second member of a homologous series of alcohols known as alkanols because they are based on the alkane structure. As well as by fermentation ethanol can be made by an addition reaction called “hydration” when a molecule of water is added to the unsaturated ethene molecule. This sort of reaction requires high temperatures and pressure and a phosphoric acid catalyst: Names and structures of alkanols can easily be worked out because they are closely related to the corresponding alkane. A hydrogen has been replaced by a new functional group ( –OH) called the hydroxyl group and the name of the alkane has the ―e‖ removed and an ― ol‖ substituted. Name of alcohol Molecular formula of alcohol methanol CH3OH ethanol C2H5OH propanol C3H7OH Structure formula of alcohol From this table you can work out the general formula of the alkanols: CnH2n+1OH 4 LI 8 Drawing and Naming Alkanols All alkanols with more than 2 carbons have isomers and therefore have different names due to the position of the hydroxyl group: propan-1-ol propan-2-ol Shortened structural formulae also show the different positions of the hydroxyl groups: Propan-1-ol - CH3CH2CH2OH Propan-2-ol - CH3CH(OH)CH3 Systematic naming rules: 1. Count the number of carbons to give the correct basic name ie 4 carbons = butanol 5 carbons = pentanol etc… 2. Count from the end which gives the lowest number to show the position of the hydroxyl group. NOTE- You will only be asked to name straight chained alkanols. Activity: Complete the following table Name of alkanol Full structural formula Butan-2-ol Pentan-3-ol 5 Shortened structural formula Properties of Alkanols LI 9 Alkanols are a homologous series therefore they have similar chemical properties and gradually changing physical properties. We will look at physical properties first: Boiling Points Using the data booklet, page 6, fill in the following table: Name of Alkanol Methanol Boiling Point (ºC) Ethanol Propan-1-ol Butan-1-ol There is a clear trend. The larger the molecule the higher the boiling point. This is similar to what we discovered with the fractions of crude oil. The larger the molecule the more energy is needed to separate the molecules from each other because larger forces of attraction have to be overcome. Boiling Points of Isomers Using the data booklet, page 6, fill in the following table: Name of Alkanol Boiling Point (ºC) Propan-1-ol Propan-2-ol Butan-1-ol Butan-2-ol Isomers have different boiling points. The position of the hydroxyl group has an effect. If the hydroxyl group is at the end of a chain the boiling point is higher so the force of attraction must be higher. The effect of the hydroxyl group can be seen even more if you compare two molecules with similar formula mass: Propane (formula mass 44) has a boiling point of (minus) - 44 ºC Ethanol ( formula mass 46) has a boiling point of +78ºC due to the attractive force of the hydroxyl group. 6 Solubility in water Methanol and ethanol dissolve well in water, they mix completely and are described as totally miscible. As the hydrocarbon chain length increases, the solubility decreases so the bigger alkanol molecules are less soluble in water. Alkanol Butan-1-ol Pentan-1-ol Hexan-1-ol Heptan-1-ol Octan-1-ol Formula C4H9OH C5H11OH C6H13OH C7H15OH C8H17OH Solubility in water in g/l 63 22 5.9 1.7 0.5 Draw a spike bar graph of the number of carbon atoms in the molecule versus the solubility in water and staple it to your booklet here. pH of Alkanols Alkanols have no effect on the balance between hydroxide ions and hydrogen ions in water therefore the pH is neutral. Uses of Alkanols Ethanol is often used as an ingredient in industry to make other compounds. It is also an important solvent in perfumes and food flavourings. Look in your kitchen cupboards and see if you can find ethanol in the ingredient lists. Propan-2-ol is also used as a solvent and you have probably used it to clean your computer screen or in a gel to sanitise your hands. Remember alkanols are poisonous to bacteria as well as us! Chemical Properties of Alkanols All alkanols burn, ethanol and methanol in particular burn very cleanly, we will be investigating the uses of alkanols as fuels at the end of this topic. Alkanols also take part in many other reactions. One very important reaction is oxidation. This oxidation reaction increases the ratio of oxygen to hydrogen in the molecule and converts an alkanol, with a hydroxyl group on an end carbon, into a new homologous series of compounds called the carboxylic acids. This reaction naturally occurs in wine when the ethanol reacts with oxygen in the air to form ethanoic acid (vinegar). This is what turns wine sour. 7 LI 10 Carboxylic Acids Carboxylic acids are a homologous series that all contain the functional group called the carboxyl group: If the carboxyl group is on an alkane chain then the name will be similar to the alkane it comes from but with an ―oic‖ ending. This family of carboxylic acids are known as the ―alkanoic acids”.To work out the name just count the carbons: Number of carbons 1 Name of carboxylic acid Methanoic acid 2 Ethanoic acid 3 Propanoic acid 4 5 Shown below is the full structural formula of the most well known carboxylic acid called ethanoic acid (vinegar): Ethanoic acid 8 Structures of Carboxylic Acids All alkanoic acids are an alkane chain with the last carbon converted to a –COOH. To draw the structure of an alkanoic acid from its name work out the number of carbons, fill them completely with hydrogen except for the last carbon which needs to be double bonded to an oxygen and single bonded to an –OH group to form the carboxyl group. Try these: Name of carboxylic acid Shortened Structural Formula Propanoic acid CH3CH2COOH Butanoic acid CH3CH2CH2COOH Full Structural formula CH3CH2CH2CH2COOH LI 11 Carboxylic Acids in the Natural World You will all have met carboxylic acids in everyday life. They are hard to miss because they are a very smelly, stingy group of compounds. The best known are: 1. Methanoic acid (old name formic acid‖) is in ant and bee stings. 2. Lactic acid is what causes milk to go sour. 3. Citric acid is in fruit. 4. Vinegar, a dilute and smelly solution of ethanoic acid. 5. Vomit!! Part of the reason vomit is so smelly is that some of the digestion products of fats are brought back up. When fats are digested a special group of carboxylic acids called fatty acids are made. 9 Uses of Vinegar Read the extract below then answer the questions: Vinegar’s role in history is well documented. This versatile product was used by everyone—from kings and conquerors to explorers and everyday people. The Babylonians used vinegar to preserve and pickle food. Hippocrates prescribed vinegar as a remedy for a variety of ailments. Caesar’s armies used vinegar as a beverage. Hannibal drenched huge boulders in hot vinegar which cracked them into small pieces, enabling his army to continue its journey across the Alps. Helen of Troy bathed in vinegar to relax. Jesus was offered vinegar before he was crucified. Early Europeans used vinegar as a deodorizer. During the Bubonic Plague people poured vinegar on their skin to protect themselves from germs. Cleopatra dissolved pearls in vinegar to prove that she could consume a fortune in a single meal. Sailors used vinegar as a food preservative during long voyages. World War I medics used vinegar to treat soldiers’ wounds. Today, people are still using white distilled vinegar in hundreds of different ways—from cooking and cleaning to gardening and the laundry. Q1. Vinegar is often used to remove lime scale. Lime scale is made of the same substance that pearls are. Suggest why vinegar is able to dissolve lime scale. Q2. Can you give two examples of foods we still preserve using vinegar. Q3. Can you suggest why vinegar was used to treat wounds and why this might be linked to its preservative effect. 10 LI 12 Making Esters One of the main industrial uses of carboxylic acids is to make compounds called esters. Esters are an important group of carbon based compounds formed by reacting a carboxylic acid molecule and an alcohol molecule together. The reaction requires a catalyst such as concentrated sulphuric acid. The "ester link" Word equation: methanol + butanoic acid ⇄ methyl butanoate (ester) + water CH3OH + C3H7COOH ⇄ C3H7COOCH3 (ester) + H2O The characteristic link between the molecules is called the ester link This type of reaction is called a condensation reaction Condensation reactions are reactions which join two molecules together by releasing a small molecule, often water A condensation reaction that makes an ester is also called esterification Condensation reactions are reversible The name of the ester comes from the alcohol and carboxylic acid that made it with the alcohol part coming first 11 Names of Esters Identify the names of the alcohol and the carboxylic acid used to make the ester, change the endings and add them together: Alcohol Name methanol ethanol propanol butanol LI 13 Ester Name methyl…… ethyl….. propyl…. butyl….. Carboxylic Acid Name methanoic acid ethanoic acid propanoic acid butanoic acid Ester Name ……methanoate …..ethanoate …..propanoate …..butanoate Properties and Uses of Esters Esters can be made easily in the lab. Once they are made they are identified due to their characteristic fruity smells and the fact that they do not mix with water and form an oily, immiscible layer. Esters are often used as food flavourings Esters are often used as perfumes Many nail varnishes contain ester solvents because they easily evaporate 12