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The purpose of this lab was to calculate the heat of formation for magnesium oxide (MgO).

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Introduction

The Heat of Formation of MgO Iqra Abbasi 11/19/2012 ________________ Heat of Formation of MgO (DCP and CE Lab) 9/28/2012 Data and Observations Table 1: Raw Data Collection: Mg(S) +2HCl (aq) →MgCl2 (aq) +H2 (g) Trial 1 Initial mass of Magnesium (Mg) g/±0.0001 0.1253 Initial temperature of HCl/°C/±0.2 22.1 Final temperature of HCl/°C/±0.2 27.4 Volume of HCl/mL/±1 100 Table 1: represents the raw data for the above equation Qualitative Observations: 1. When the magnesium strip was added in the hydrochloric acid, the resulting reaction was bubbling and a release of gases 2. Saw the release of gases as vapor, a distinct smell like rubber 3. After a minute or so, the reaction ceased as the magnesium strip dissolved and the hydrochloric acid returned to the same consistency as water but remained bubbly Table 2: Raw Data Collection: MgO(S) +2HCl (aq) →MgCl2 (aq) +H2O (g) Trial 2 Initial mass of Magnesium Oxide (MgO) g/±0.0001 1.5064 Initial temperature of HCl/°C/±0.2 21.9 Final temperature of HCl/°C/±0.2 33.5 Volume of HCl/mL/±1 100 Table 2: represents the raw data for the Magnesium oxide Qualitative Observations: 1. When the magnesium oxide powder was added to the hydrochloric acid, there was no immediate reaction 2. ...read more.

Middle

Solution: QHCl = mHCl. cHCl. âTHCl QHCl = 100g×4.18J/g°C×11.6°C QHCl= 418J/°C × 11.6°C QHCl= 4848.8 J QHCl= 4.8488 kJ 1. Calculate the moles of the MgO burned. 2. Solution: nMgO = nMgO = nMgO = 0.03737mol ± 0.0066% nMgO = 3.73x10-2 mol±0.0066% 1. Calculate the molar heat of formation of MgO in kJ/mol. Use Molar heat = Q (in kJ) / mol of wax. Remember to convert to kJ 2. Solution: âHMgO = âHMgO= âHMgO = -129.75kJ/mol±4.446% Table 6: Final Uncertainty Calculations for Trial 1 Uncertainty Calculations Percent Uncertainty Absolute Uncertainty Total uncertainty of Q 4.44% Moles of magnesium oxide (MgO) 0.0066% Uncertainty of âHMgO 4.44% +0.066% = 4.446% 129.75kJ/mol x 0.044446 = ± 5.7686 Therefore the âHMgO is -1.3 x 102 ± 6.0 kJ/mol Calculate the âH of the equation H2 (g) + ½ O2 (g) → H2O (l) Using Hess’s Law: âHf (reactants) - âHf (products) âHf (reactants) - âHf (products) = -286 kJ/mol Table 7: results of âHf for all equations âHf/ Reaction magnesium -429.841 ± 37.0515 kJ/mol Mg(S) +2HCl (aq) →MgCl2 (aq) +H2 (g) magnesium oxide -129 ±5.7686 kJ/mol MgO(S) +2HCl (aq) →MgCl2 (aq) ...read more.

Conclusion

Another reason to conduct this experiment in a closed system would be because the temperature in the room where the experiment was conducted may have fluctuated creating inconsistency within our calculations. There was also the assumption that the density of the hydrochloric acid was the same as water. If the proper or accurate density was used, there could have been more accurate results. These minimal errors can be evaded in further investigations by changing some of the equipment used to gather data. To ensure that a proper temperature is recorded, a temperature probe with uncertainty in the hundredth decimal place would give accurate results. Another way to minimize error would be do a different set-up to make certain that heat loss is prevented. To do that, instead of using a Styrofoam cup, a calorimeter can be used. If a calorimeter is unavailable, than adding a lid to the cup would diminish the error significantly. Another way to further improve the experiment would be to determine the actual density and specific heat of HCl, by doing this our results would be more accurate in terms of the solution used. ...read more.

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