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Determining an enthalpy change of reaction

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Determining an enthalpy change of reaction Design Aim The purpose of this experiment is to determine the enthalpy change for the displacement reaction: Zn(s) + Cu2+(aq) � Cu(s) + Zn2+(aq) Introduction By adding an excess of zinc powder to a measured amount of aqueous copper (II) sulphate, and measuring the temperature change over a period of time, you can than calculate the enthalpy change for the reaction. Requirements ? safety spectacles ? pipette, 25 cm3 ? pipette filler ? polystyrene cup with lid ? copper (II) sulphate solution, 0.5 M CuSO4 (harmful if swallowed) ? weighing bottle ? spatula ? zinc powder ? balance ? thermometer, 0-100?C (0.1? graduations) ? watch or clock with second hand Procedure 1. Pipette 25.0 cm3 of the copper (II) sulphate solution into a polystyrene cup. 2. Weigh about 1 g of zinc powder in the weighing bottle. Since this is an excess, there is no need to be accurate. ...read more.


At the 180-second interval, we added the zinc. It first floated on the surface of the solution but as we continued to stir, it mixed with the solution, taking on a shade closer to brown. The solution reflected that same brown color as we started but then changed color too, taking on a darker tinge of blue. By the end of the experiment, we could observe excess zinc resting on the bottom of the cup. The solution had actually turned shades lighter. Data Processing: I will first calculate the averages of all three sets of trials to represent the temperature change of the solution. I will then plot the temperature (y-axis) against time (x-axis), as well as extrapolate the curve to 3.0 minutes to establish the maximum temperature rise. Next, I will calculate the enthalpy change for the quantities used, making appropriate assumptions. Finally, I will calculate the enthalpy change for one mole of Zn and CuSO4(aq), and write the thermochemical equation for the reaction. ...read more.


Sample calculations: error = [(-99.87 - (-217)) / (-217)] x 100% = 53.98 My calculations revealed that there was a percentage error of over 53%. Limitations Suggestions for Improvement Heat continued to escape from top of the cup Maybe place a lid on the cup to contain the heat within the cup and that way not much heat is being lost or use a calorimeter if it were possible to obtain one When calculating the enthalpy energy of the reaction, we substituted C with the specific heat capacity of water. By using the actual specific heat capacity of the CuSO4 solution We substituted the amount of zinc powder as dictated by the experiment sheet (6g) with only 1g. Perhaps, this significantly lower concentration of zinc can be held accountable for the significantly low deviation in degrees after the zinc was added. Actually add 6 grams of zinc which is the approximate equivalent of 1 mol of zinc and what was asked for by the experiment sheet. The change in temperature might result in the expected maximum temperature and greater degrees between each time interval. ?? ?? ?? ?? ...read more.

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