Electricity and Magnetism Essay Example for Free

Electricity and Magnetism Essay In this investigation I will be burning a range of alcohol in a method known as calorimetry. This will allow me to see the amount of energy produced by each alcohol, and then look at the structure of the alcohol and investigate why an amount of energy is produced for each alcohol. Before I go on with the experiment there are several factors that must be first understood. What is an alcohol? The definition of an alcohol as taken from Richard Harwoods Chemistry textbook is a series of organic compounds containing the functional group OH. The OH group, called a hydroxyl group is what defines the compound as an alcohol. The alcohol compounds are very similar to the alkanes, however alcohols contain one oxygen atom, creating the hydroxyl group, and making the alkane an alkanol (alcohol). As the hydroxyl group makes the compound different to an alkane, the hydroxyl group is seen to be functional. The formula for alcohol is: In this investigation I will look at the first five alcohols. These are methanol, ethanol, propan-1-ol, butan-1-ol and pentan-1-ol. The classification of alcohols is similar to the classification of alkanes, where the name refers to the number of carbon atoms i. e.meth- one carbon atom, eth-=two carbon atoms, prop-=3 carbon atoms, but-=four carbon atoms, pent-=five carbon atoms and so on. The carbon atom that the hydroxyl group is bonded to may classify the alcohol further. If it is joined to the end carbon atom it is classified as -1-ol, if it is bonded to the second carbon atom it is classified as -2-ol and so on. The five alcohols I am testing are shown with formulas, and atomic structure diagrams below: Name RMM Formula Structure Boiling Point Methanol. What is combustion? The definition of combustion as taken from Richard Harwoods Chemistry textbook is a chemical reaction in which a substance reacts with oxygen the reaction is exothermic. Burning is a combustion reaction that produces a flame. The reactions that will take place in our investigation will be combustion reactions, as we burn the alcohol in calorimetry. The combustion of an alcohol produces carbon dioxide and water. This is represented by the following equation: ALCOHOL + OXYGEN i CARBON DIOXIDE + WATER e. g. The combustion of methanol produces carbon dioxide and water: METHANOL + OXYGEN i CARBON DIOXIDE + WATER 2CH3OH + 3O2 i 2CO2 + 4H2O What is calorimetry? Calorimetry is defined as the science of heat. It may be used in chemistry to measure the heat energy exchanged for a substance during a reaction, by allowing the substance reacting to heat a measured mass of liquid. The temperature change of this liquid is measured and recorded, and the following equation may be used to calculate the heat energy transferred to the liquid: Heat change = MC? T (where M = mass of liquid, C = critical temperature, and T = temperature change). The critical temperature is the proportionality between heat energy applied and the subsequent temperature rise. E. g. for 1g of water a temperature rise of 1 i C requires 4. 8 joules of heat energy. Using calorimetry may be used to measure both reactions in solution, and reactions not in solution. Wet reactions or those in solution are more accurate than those not in solution, as the actual energy release of the reaction is being measured directly as a thermometer is placed in the solution. For dry reactions, (a reaction not in solution such as the burning of an alcohol) the reaction must be used to heat a mass of water and the temperature increase measured from the water. As the combustion reaction must transfer its heat energy from the reaction to the water, calorimetry for dry reactions can be inaccurate due to heat loss. HYPOTHESIS I believe that the increased complexity of a molecule and the energy released by it are proportional. I found this idea upon the theory of breaking and making bonds. In a molecule, bonds hold atoms together. When these bonds are formed energy is given out to the surroundings (exothermic), and when these bonds are broken energy is absorbed from the surroundings (endothermic). This may be seen by the alcohols boiling points: Name Boiling Point Methanol 65 Ethanol 78 Propan-1-ol 97 Butan-1-ol 117 Pentan-1-ol 137 Using this theory of breaking/making bonds, we can say that there will be a greater amount of energy released from the combustion of a more complex alcohol, as more bonds will be formed. When more bonds are formed, more heat energy is released. The hypothesis may be seen on the flowing graph: TESTING To investigate the relationship between the structure and heat provided by combustion of a range of alcohols, we will use the method of calorimetry. We will do this by burning an alcohol, and allowing it to heat a mass of water. Measuring the temperature rise of this mass of water we can use the formula to find the heat energy released during the reaction. Apparatus == 1 can == 1 measuring cylinder == Water == 1 thermometer == 1 stand == 1 clamp == 1 boss == 1 heat mat == 1 alcohol burner/candle == 1 balance == Draught shields Fig1: Experiment setup. Method. Safety must be ensured at all times, as highly flammable substances are being burned here. All students must wear eye protection during the experiment, stay standing during the experiment, and be aware of the flames around them. 1. The apparatus is set up as shown in fig 1. 2. The alcohol candle is weighed on the balance, and the mass recorded. 3. The mass of water in the can measured and recorded 4. The height between the candlewick, and the base of the can must be set and recorded, measuring the distance with a ruler. 5. The temperature of the water is measured and recorded using the thermometer. 6. The candle is lit and the thermometer monitored until the water has risen by a given temperature. 7. The candle is blown out, the burnt wax on the base removed of the candle, and the candle is weighed. The data produced by this method will then be calculated by the formulas: ? H (j) = mass of water (g) X specific heat capacity of water (S. H. C) X temperature rise (? C) The result of this is found per gram of alcohol burnt by dividing it by the change of mass ? H per gram of alcohol burnt (J/g) = ? H (? C) / change in mass (g) The results of this are the found per mole of alcohol burnt. ? H per gram of alcohol burnt per mole (J/mole) = ? H per gram of alcohol burnt (g) X RMM of alcohol Variables There are two types of variables: dependant variables and independent variables. Dependant variables are those that are kept constant at a set value, so that they cannot cause variation in the results, by changing throughout the experiments. There should only be one independent variable in a test, this is what is being tested. Therefore the dependent variables for this investigation are as follows (see fig 2): 1. The distance of the wick from the base of the can The distance of the flame from the base of the can may vary the results greatly, as it will decide how much of the flames heat is transferred directly to the can and to the water. The experiment should allow the flame to contact the can at its hottest point. The most accurate and safe way to measure flame distance from the can is to measure the distance of the wick. For the purposes of our experiment this should be accurate enough. Measuring the distance from the wick and the base of the can each time will control this variable. 2. The mass of water heated. The volume of water can vary the experiment greatly, as the greater the mass of water used, the more alcohol will be combusted to reach the target temperature. Also when a greater mass of water is used, the test will go on for longer, and thus a greater amount of energy will be transferred to the surroundings as wasted energy. Measuring the amount of water used each time will control this variable. 3. The type of can used. The type metal the can is made from is extremely important to the experiment, as different metals conduct heat with different efficiency and at different rates. Therefore the type of can used will affect the heat transfer to the water. Using the same can each time will control this variable. 4. The heat increase The heat increase can vary the experiment, as the greater the energy increase, the greater the mass of alcohol burnt, and the greater amount of energy transferred to the surroundings as waste. The start temperature may affect the results, as the higher the temperature the equipment reaches, the more heat will be wasted in the surroundings, according to the theory that heat energy moves from areas of high heat energy to areas of low energy. By allowing the equipment to cool after each experiment to a set temperature this variable may be controlled. 5. Stirring of the water Stirring the water will affect the results, as it means that the whole mass accounted for in the calculation will be being heated, not just one volume of water. The type of stirring in terms of frequency and power may affect the results also, and must be kept constant. To control this variable, the same type of stirring will be used each time. The only variable in the experiment will be the changing type of alcohol being combusted, as this is what is being investigated.