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Download unit 2c File - Uddingston Grammar School
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National 4/5 Sub-topic 2c-Everyday Consumer Products Summary Photosynthesis Plants make their own food by photosynthesis. This process is a chemical reaction y that uses light energy. lkkkkkrhggdf All green plants contain a chemical in their leaves called chlorophyll. Chlorophyll is extremely important to the plant as it absorbs sunlight. The plant then uses this light energy from the sun during the reaction of carbon dioxide and water to make glucose and oxygen. light Carbon dioxide + water glucose + oxygen chlorophyll Glucose is a carbohydrate and is the food for the plant. The plant either uses the glucose immediately or converts it into larger molecules of starch. Carbohydrates Carbohydrates are compounds which contain carbon, hydrogen and oxygen, with the hydrogen to oxygen ratio of 2:1 Name of carbohydrates Formula Glucose C6H12O6 Fructose C6H12O6 Sucrose C12H22O11 Maltose C12H22O11 Starch (C6H10O5)n If you look at the molecular formula you should notice that glucose and fructose are isomers, since they have the same molecular formula but different structural formula. Sucrose and maltose are also isomers. 1 Properties of Carbohydrates The Tyndall effect occurs if you shine a flashlight through a jar of liquid and see the light beam. In glucose solution the particles are too small to affect the light. In starch the particles are larger and don’t dissolve well. glucose starch This is called a colloidal solution. The large, insoluble starch particles scatter the light. Glucose Sucrose Starch Appearance white solid white solid white solid Taste sweet sweet not sweet Solubility soluble soluble insoluble Type of Solution true true colloid pH neutral neutral neutral Iodine test No colour No colour Brown to change change blue/black Clear blue to No colour No colour brick red change change Benedict’s test precipitate Reducing Sugars Glucose and fructose and maltose give a positive result in the Benedict’s test. These sugars are sometimes known as Reducing Sugars because they change benedicts solution from blue to orange. 2 Respiration All cells in living things break down glucose to provide the energy that cells need. This process is called respiration and is the opposite chemical reaction to photosynthesis. It requires the gas oxygen. We take in this gas through our lungs. It also requires glucose, which comes from the digestive system. The oxygen and glucose is then carried by our blood to the cells where respiration occurs to release the energy the cells require. The word equation for the reaction is:- Glucose + oxygen carbon dioxide + water + ENERGY The energy produced in respiration is used by animals to – move about, – produce heat to provide warmth, - to send messages through the nerves to and from the brain 3 Balancing carbon dioxide and oxygen in the air Since respiration is the opposite of photosynthesis, they maintain a balance of oxygen and carbon dioxide in the air. • Photosynthesis and respiration are important in maintaining the correct balance of carbon dioxide and oxygen in the air. • Trees and other plants take in carbon dioxide and convert it to oxygen. • Extensive clearing of forests is dangerous to life on Earth because less carbon dioxide is removed from the atmosphere. • High levels of carbon dioxide in the atmosphere can lead to global warming caused by the greenhouse effect. Burning Carbohydrates • When carbohydrates burn, they react with oxygen in the air to produce carbon dioxide and water. • This is an exothermic reaction because energy is released. • The carbon in the carbon dioxide must have come from the carbohydrate proving that carbohydrates contain carbon. • The hydrogen in water must come from the carbohydrate so this proves that carbohydrates contain hydrogen. • The oxygen could have come from the air, so this experiment does not prove that there is oxygen in carbohydrates. Hydrolysis When we eat carbohydrates, e.g. pasta, rice, we are eating large starch molecules. Starch molecules are too large and insoluble to fit through the gut wall and so are broken down by the body into small soluble glucose molecules which can pass through the gut wall. 4 Hydrolysis of Starch Starch molecules break down by reacting with water molecules. The breakdown of starch is an example of hydrolysis. Hydrolysis is the breaking down of a large molecule into smaller molecules using water. The body uses the enzyme amylase to break the starch down at body temperature. Enzymes are biological catalysts that breakdown complex food molecules into smaller ones in the digestive system. In the lab, starch can be broken down using dilute acid. The digestion of sucrose is also an example of hydrolysis. Sucrose G = Glucose F = Fructose Alcoholic Drinks Yeast cells contain enzymes that convert sugars (such as glucose and sucrose) into alcohol (ethanol) and carbon dioxide. The enzyme acts as a catalyst for the reaction. This reaction is called FERMENTATION. Glucose C6H12O6(aq) ethanol + carbon dioxide C2H5OH(l) + CO2(g) The alcohol produced by fermentation is called ethanol. It is a member of the alkanol family and has the formula C2H5OH. 5 The volume of ethanol produced during fermentation is low. This is because once the concentration of alcohol reaches 14% it kills the yeast which stops the production of alcohol. So in fermentation, only drinks around 14% can be made. Any fruit, vegetable or grain which contains starch or sugars can be fermented to produce an alcoholic drink. Fruit/ vegetable/ grain Grapes Potatoes Apples Barley Alcoholic Drink Wine Vodka Cider beer % Alcohol 9-14 40 3-7 3-5 Distillation Distillation is used to increase the alcohol concentration of fermentation products. Water and alcohol can be separated by distillation because they have different boiling points (water 100ºC, alcohol 79 ºC) For drinks called spirits such as vodka and gin a higher concentration of alcohol is needed, usually around 40%. Enzymes cannot produce this concentration so the fermentation liquid must be distilled. Water boils at 1000C but ethanol boils at 790C so during distillation, the fermentation liquid is heated slowly. The ethanol boils first and is separated from the rest of the watery liquid. This is then made into the spirit required. Optimum Efficiency of Enzymes Enzymes are very fussy. They only work within a very limited temperature and pH. National 4/5 As you can see in the graph after a certain temperature or pH an enzyme will stop working and at this point we call them denatured. The pH or temperature at which an enzyme works best is called its optimum pH or optimum temperature 6 National 5 Types of Alcohol The alcohol produced by fermentation of carbohydrates should be called ethanol. It is only one of a family of similar compounds called the alkanols. The alkanols form a homologous series. They can all be represented by a general formula CnH2n+2O or The members of the alkanol series all have similar chemical reactions, and the physical CnH2n+1OH properties like boiling point, melting point and density show a regular change as the size of the molecule increases. Alkanols have the hydroxyl group (-OH) Alkanols Name Methanol Chemical Formula CH3OH Full Structural Formula Shortened Structural Formula Ethanol C2H5OH CH3CH2OH Propanol C3H7OH CH3CH2CH2OH Butanol C4H9OH CH3CH2CH2CH2OH Pentanol C5H11OH CH3CH2CH2CH2CH2OH Hexanol C6H13OH CH3CH2CH2CH2 CH2CH2OH Heptanol C7H15OH CH3CH2CH2CH2CH2CH2CH2OH Octanol C8H17OH CH3CH2CH2CH2CH2CH2CH2CH2OH CH3OH 7 Naming Alkanols Alkanols are named more specifically by the position of the hydroxyl (-OH) group. e.g. Butan-2-ol Butan-1-ol Hexan-3-ol Pentan-1-ol Properties and Uses of Alcohols As alcohols increase in size their physical properties, like boiling point and viscosity, show a gradual change. Alcohols are very good solvents, they are used as cleaning fluids to dissolve oils, eg can be used to clean computer keyboards and monitor screens Propan-2-ol is used in many hand gels and disinfectant wipes as it evaporates quickly and is relatively non-toxic. Alcohols burn with a blue flame Alcohols can be used as fuels In Brazil ethanol produced by the fermentation of cane sugar can be dehydrated (removal of water) to produce ethene. This ethene can be used to produce poly(ethene) resin and other plastics. 8 Alcohol as a Fuel Alcohols can be used as fuels since they burn with a very clean flame. A fuel releases energy on reaction with oxygen. This type of reaction, known as burning (or combustion), is exothermic. Exothermic reactions release energy to their surroundings. Endothermic reactions take in energy from their surroundings Fuels can be compared by measuring the energy given off when they are burned. The energy released in the burning of a fuel can be calculated by using the heat energy to raise the temperature of a known mass of water. The heat energy released where c m = c m ΔT = specific heat capacity of water = 4.18 kJ kg-1 oC-1 = mass of water absorbing heat (1 cm3 of water has a mass of 0.001 kg) ΔT = temperature change Example: Calculate the heat released on the burning of a fuel that raises the temperature of 100 cm3 of water by 10.5 oC. Heat released = c m ΔT = 4.18 x 0.1 x 0.05 = 4.39 kJ In the lab, the calculated energy released is less than the actual energy released because some energy is lost to the surroundings, e.g. the container for the fuel and the air. 9 Comparing Energy Released The energy released from the burning of different fuels can be compared by calculating the energy released for the burning of one mole of each. Alcohol methanol ethanol propan-1-ol Molecular formula Energy produced ( kJmol-1) CH3OH C2H5OH C3H7OH 727 1367 2020 The energy produced increases as the size of molecule increases. The energy increases by a regular amount since each alkanol differs by –CH2 each time. Carboxylic acids Another homologous series is the carboxylic acids. The characteristic group that gives the characteristic properties to the carboxylic acids is the carboxyl group: Each member of the carboxylic acid series has a name which ends in -anoic acid and a prefix which indicates the number of carbon atoms in the molecule, The characteristic carboxyl group must always be at the end of a carbon chain. 10 Carboxylic Acids Name Methanoic acid Chemical Formula Full Structural Formula Shortened Structural Formula HCOOH HCOOH CH3CH2COOH Ethanoic acid Propanoic acid CH3COOH CH3CH2CH2COOH C2H5COOH CH3CH2CH2CH2COOH Butanoic acid C3H7COOH CH3CH2CH2CH2CH2COOH Pentanoic acid C4H9COOH Hexanoic acid C5H11COOH Heptanoic acid CH3CH2CH2CH2 CH2CH2COOH CH3CH2CH2CH2CH2CH2CH2COOH C6H13COOH CH3CH2CH2CH2CH2CH2CH2CH2COOH Octanoic acid C7H15COOH Vinegar is a solution of ethanoic acid in water. Vinegar can be used as a preservative i.e. pickling food to make it last longer. Many household cleaners contain vinegar. Benzoic acid is found in foods such as raspberries and tea but it is also added to other foods as a preservative. Citric acid is found in citrus fruits. 11 Esters Esters are the products of reactions between alcohols and carboxylic acids. Esters have characteristic smells and are insoluble in water. Esters are used as flavourings and solvents. An ester takes its name from the alcohol and carboxylic acid from which it can be made. The name contains the ending -yl (from the alcohol) and -oate (from the carboxylic acid). e.g. alcohol: methanol acid: ethanoic ester: methyl ester: ethanoate name: methyl ethanoate The structure is based on the parent carboxylic acid and alcohol; remove the -OH from the carboxyl group and the -H from the alcohol. Note that the structure of the alcohol has been turned round. acid alcohol Since esters are prepared from alcohols and carboxylic acids, all esters contain the functional group: from acid from alcohol 12 When written the other way round, the functional group looks like: from acid from alcohol Esters can be named from their structure. e.g. from alcohol from acid alcohol: ethanol acid: propanoic ester: ethyl ester: propanoate name: ethyl propanoate from acid from alcohol alcohol: propanol acid: methanoic ester: propyl ester: methanoate name: propyl methanoate 13 Making Esters The following apparatus would be used to make an ester. Alkanol + carboxylic acid Ester + Water Forming an ester is an example of a condensation reaction In a condensation reaction, two molecules are reacted together to produce a larger molecule with the loss of water. 14
