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Investigation of Energy Changes in a Displacement Reaction.

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Introduction

January 2002 Michael Lavery U5W Chemistry Coursework - Investigation of Energy Changes in a Displacement Reaction. Plan Introduction When a metal is added to a solution of another salt metal the reaction between the two brings about an exothermic reaction. In this investigation I aim to discover, as the mass of zinc increases, when energy given out stops rising i.e. how much zinc can react with 50cm3 of 0.5M Copper Sulphate. The reaction is exothermic because energy given out when bonds are made is greater than the energy taken in to break bonds. Zinc + Copper Sulphate ? Zinc Sulphate + Copper ? ? (metal) (metal salt) Zn (s) + CuSO4 (aq) ? ZnSO4 (aq) + Cu (s) Variables The only variable I will alter throughout the experiment is the mass of zinc used; altering only one variable keeps the test fair. I will keep the following variables constant: Volume of copper sulphate used (50cm3) and the concentration of copper sulphate (0.5M) Method Apparatus * Large glass beaker * Polystyrene cup * Thermometer * Measuring Cylinder * Copper sulphate (0.5M) * Zinc (powder) * Small glass beaker * Mass balance * Spatula Diagram 1. Using the measuring cylinder measure out 50cm3 of copper sulphate and pour this into the polystyrene cup which is in the glass beaker (as shown in the diagram). ...read more.

Middle

energy given out must occur when the copper sulphate is reacted with 0.025 moles of zinc, the following graph shows how the energy released in the reaction stops increasing when 0.025 moles of zinc has been added even though the amount of zinc added continues to rise. To find the mass of zinc that produces the largest amount of energy released I must calculate what mass of zinc contains 0.025 moles. Relative atomic mass of zinc ? Mass of 0.025 moles of zinc = 0.025 x 65 = 1.625g So maximum energy will be given out when 1.625 g of zinc is added to 50cm3 of 0.5M copper sulphate. When plotting a graph of mass of zinc against energy given out I can use the following equation: Energy given out = m x s x temperature rise ? ? Mass of solution Specific heat capacity (4.2) Results Mass of zinc (g) Initial temperature (?c) Final temperature (?c) Temperature rise (?c) Average Temperature rise (?c) Energy given out (joules) 0.5 20 27 7 7 1470 19.5 26.5 7 1.0 19.5 34.5 15 15 3150 19 34 15 1.5 20 42 22 22.5 4672.5 19 41.5 22.5 2.0 16 43 27 27.25 5722.5 16.5 44 27.5 2.5 15.5 44.5 29 29 6090 16 45 29 3.0 15.5 45 29.5 29.25 6142.5 16 45 29 3.5 17.5 47 29.5 29.5 6195 18 47.5 29.5 4.0 18 47 29 ...read more.

Conclusion

* I could have improved the measurements of my copper sulphate by using either a pipette or a burette, these pieces of equipment are more complicated but much more accurate. * If I had used a mass balance which read to three decimal places my measurements of zinc, especially the low ones, will have been much more accurate. * A lid on the polystyrene cup would have stopped so much heat escaping but stirring during the reaction would have been a problem. * During the experiment I only but a glass beaker around the cup to stop heat escaping, accuracy would have increased if more lagging was included. * More repetition of the experiment would improve accuracy because averages would be more reliable, repetition would also make anomalous points on the graph less likely. * More masses of zinc would improve my graph, if I had increased the amount of zinc by 0.25g instead of 0.5g the results may have related to my prediction and theory better. * Using different concentrations of copper sulphate as well as masses of zinc would have been time-consuming but would have produced better results. * Other types of displacement reactions to compare this with would help to prove my prediction; I could use different metals and different metal salts. * I could use a temperature probe connected to a computer with a magnetic stirrer in the solution, this would greatly improve accuracy, the diagram below shows how such an experiment would be set up. ...read more.

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