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Classic chemistry experiments 85. 219 Comparing the heat energy produced by combustion of various alcohols Topic Exothermic reactions, bond formation, bond breaking, heats of reaction/combustion. Timing 60 min. Description Students use the combustion of known amounts of various alcohols to heat a known amount of water. Apparatus and equipment (per group) ▼ Retort stand ▼ Boss ▼ Clamp 3 ▼ 250 cm Conical flask or metal calorimeter ▼ Thermometer ▼ Spirit burners. Chemicals (per group) Methanol (Highly flammable) Ethanol (Highly flammable) Propanol (propan-1-ol) (Highly flammable) Butanol (butan-1-ol) (Highly flammable). Teaching tips Stress the importance of fair testing, for example the height of the calorimeter above the wick. More able students can work out the number of moles used and find the energy produced per mole. A temperature sensor attached to a computer can be used in place of a thermometer. It can plot the temperature change on a graph and allow better quantification of the heat produced. Background theory Energy changes, exothermic and endothermic reactions, reactions involving bond breaking and bond formation. For more advanced students bond enthalpies. Energy change = mass of solution x specific heat capacity x temperature change. Safety Wear eye protection. Spirit burners are the safest way of burning the alcohol but students should not be allowed to fill them. Use spirit burners with a wide base. Spirit burners should be filled by a technician in the preparation room and labelled. No stock bottles of alcohol should be allowed in the laboratory. Answers 1. Butanol. 220 Classic chemistry experiments Comparing the heat energy produced by combustion of various alcohols Introduction The combustion of alcohol produces energy. This experiment compares the amount of heat produced by the combustion of various alcohols. Thermometer Clamp Conical flask Spirit burner Alcohol What to record Alcohol Initial temp/°C Final Temp Initial temp/°C change/°C mass/g Final mass/g Mass used/g Methanol Ethanol Propanol Butanol What to do 3 1. Fill the conical flask with 100 cm of water. Clamp the flask at a suitable height so that the spirit burner can be easily placed below. 2. Weigh the spirit burner (and lid) containing the alcohol and record the mass and name of the alcohol. 3. Record the initial temperature of the water using the thermometer. 4. Place the spirit burner under the conical flask and light the wick. Classic chemistry experiments 221 5. Allow the alcohol to heat the water so the temperature rises by about 40 °C. 6. Replace the cap to extinguish the flame. 7. Reweigh the spirit burner and cap and work out the mass of alcohol used. 3 Repeat for different alcohols. Use 100 cm of new cold water each time. Safety Wear eye protection. Do not open the spirit burner. Question 1. Which fuel provides the most energy per gram?