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To determine the heat of formation of calcium carbonate

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Introduction

Chemistry Lab report 1) Experiment No: 8B 2) Objective: To determine enthalpy change of hydration of magnesium sulphate(VI) 3) Date: 26th Nov, 2010 4) Theory: A) In the 1st part, an accurately weighed known mass of anhydrous magnesium sulphate(VI) powder is added to known volume of deionized water. With the help of the data of temperature change during the addition, the molar enthalpy change of solution of anhydrous magnesium sulphate(VI) can be calculated. ( H1) B) In the 2nd part, an accurately weighed known mass of magnesium sulphate(VI)-7-water powder is added to known volume of deionized water. With the help of the data of temperature change during the addition, the molar enthalpy change of solution of magnesium sulphate(VI)-7-water can be calculated. ...read more.

Middle

x (-9) x (0.025)-1 = -152.70 kJ mol-1 The molar enthalpy change of solution of magnesium sulphate(VI)-7-water = mc T x (no. of mol)-1 = (100 x 4.2 + 3.21 x 1.3) x (1.5) x (0.025)-1 = 25.45 kJ mol-1 By Hess's law, H = H1 - H2 = -178.15 kJ mol-1 The molar enthalpy change of hydration of magnesium sulphate (VI) = -178.15 kJ mol-1 Discussion: (1)~(3) is answered above 4) What assumption have you made in your calculation? Assumed: * The thermal capacity of the beaker is negligible. * The specific heat capacity of the 2 resulting solutions are the same as water, and they also weight 1 g/cm3 * The weight of the solids which dissolved in deionized water does not affect the total mass of the solution. ...read more.

Conclusion

* Some solid might not dissolve quickly enough and thus heat was lost. The improvement was using the reactants in powder form or tiny crystal form abut not bigger one, such that they could be dissolved quickly enough. * Some heat might e lost to 1st part or gained in 2nd part. The improvement was insulate the beaker or use a vacuum flask calorimeter. 6) Why cannot the molar enthalpy change of hydration of magnesium sulphate(VI) be measured directly in the laboratory? Because it was not possible to form magnesium sulphate(VI)-7-water from anhydrous magnesium sulphate(VI) and water because the anhydrous saly may dissolved in water instead. Conclusion: By using the experimental result, the molar enthalpy change of hydration of magnesium sulphate(VI) is -178.15 kJ mol-1 -End of report- ?? ?? ?? ?? ...read more.

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