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The Enthalpy of Neutralization

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Introduction

Enthalpy of Neutralization Data Collection Experiment 1 - The reaction between hydrochloric acid and sodium hydroxide. Table 1.1: Temperature of HCl and NaOH, separately and after mixing Reagent Temperature (�C) for Trial 1 Temperature (�C) for Trial 2 25cm3 of 2.00mol�dm-3HCl 21 � 0.5 21 � 0.5 25cm3 of 2.00mol�dm-3NaOH 21 � 0.5 21 � 0.5 Mixture of HCl and NaOH 34 � 0.5 34 � 0.5 Change in temperature (?T) -13 � 1.0 -13 � 1.0 Experiment 2 - The reaction between hydrochloric acid and potassium hydroxide. Table 2.1: Temperature of HCl and KOH, separately and after mixing Reagent Temperature (�C) for Trial 1 Temperature (�C) for Trial 2 25cm3 of 2.00mol�dm-3HCl 20 � 0.5 21 � 0.5 25cm3 of 2.00mol�dm-3 KOH 20 � 0.5 21 � 0.5 Mixture of HCl and KOH 32 � 0.5 33 � 0.5 Change in temperature (?T) -12 � 1.0 -12 � 1.0 Experiment 3 - The reaction between nitric acid and sodium hydroxide. Table 3.1: Temperature of HNO3 and NaOH, separately and after mixing Reagent Temperature (�C) for Trial 1 Temperature (�C) for Trial 2 25cm3 of 2.00mol�dm-3 HNO3 20.5 � 0.5 21 � 0.5 25cm3 of 2.00mol�dm-3NaOH 20.5 � 0.5 21 � 0.5 Mixture of HNO3 and NaOH 33 � 0.5 34 � 0.5 Change in temperature (?T) -12.5 � 1.0 -13 � 1.0 Experiment 4.1 - The reaction between sulfuric acid and 2.00mol�dm-3 sodium hydroxide. ...read more.

Middle

x (4.18J�g-1�k-1) x (-12.75) = -2665J (-12.5 + -13) � 2 Conversion of Uncertainty to Relative Error [(Nearest unit of volume measurement observed � desired volume) x 100 = Percentage error of volume] (1�50) x 100= 2% [(Nearest unit of temperature measurement observed � recorded temperature) x 100 = Percentage error of recorded temperature] (1�12.75)x100= 7.8% [Percentage value of volume error + percentage value of temperature error = relative error] 2%+7.8% = 9.8% relative error Enthalpy change in joules with relative error percentage Q= -2665J � 9.8% Conversion of Relative Error to Absolute Error (2665�100) x 9.8= 261 Absolute Uncertainty = �261J --> Q= -2665J � 261J (�1000) [To change to kilojoules] Q= -2.67 kJ � 0.261kJ (�0.050mol H2O) [To find kilojoules per mole of water] Q = -53.4 kJ�mol-1 H2O (� 5.22 kJ�mol-1 H2O) Calculating Percentage Error of Observed Enthalpy Value [(Observed Value - Expected Value) � Expected Value] x 100 = Percentage error [(-53.4 kJ�mol-1 H2O (� 5.22 kJ�mol-1 H2O) - -57.6 kJ�mol-1) � -57.6 kJ�mol-1] x 100 = 7.47% Experiment 4.1 - Enthalpy of neutralization for sulfuric acid and 2.00mol�dm-3 sodium hydroxide 2NaOH(aq) + H2SO4(aq)--> Na2SO4(aq) + 2H2O(l) Finding the Moles of Water Moles of sulfuric acid: [Volume x Concentration] 0.025dm3 x 2.00mol�dm-3 = 0.050mol H2SO4 Moles of sodium hydroxide: [Volume x Concentration] 0.025dm3 x 2.00mol�dm-3 (x 2) = 0.100mol NaOH Moles of water: [Equal to moles of limiting reagent] 0.050 H2SO4 --> 0.050mol H2O (x2) ...read more.

Conclusion

volume, while our thermometer had an uncertainty of plus/minus 0.5�C, giving us a varying absolute error value depending on our recorded result. Evaluation As stated in our conclusion, there were many possible sources our errors throughout the experiment could have come from. Systematic errors include the degree of precision for our instruments and materials, and we could improve the experiment's accuracy by having simply more precise equipment such as measuring beakers with a 0.05ml uncertainty rather than 0.5ml, or a data logger to measure temperature rises rather than having students observe and measure, making the reading susceptible to random errors such as parallax and simply human error. Another factor not taken into account was the room temperature, though kept more or less even, it was not constant, and therefore could have affected the experiment's results if it had changed the temperature of the reagents or final solution by even one degree. To improve on this possible error, we could attempt the experiment in a space where the temperature is constant. Seeing as temperature would be a prime affected factor in the experiment we also have to take into account the fact that by simply touching the materials (measuring beakers, thermometers etc.) that we may also be passing heat on through means of conduction by our own bodies/hands. So to improve upon this, we could have attempted the experiment wearing insulating gloves to reduce heat given off by ourselves to the materials. ?? ?? ?? ?? IB Chemistry 2 1 ...read more.

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