Determing the Enthalpy of Neutralization

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Determining the enthalpy of neutralization by calorimetry

Anam Iqbal
Partner’s name: Danielle Hodgson
TA’s name: Karinna
Section # 003
Due date: November 24, 2009

Introduction
The purpose of the experiment is to determine the enthalpy of neutralization reactions by calorimetry. Calorimetry, is the science of measuring the amount of heat. All calorimetric techniques are therefore based on the measurement of heat that may be generated (exothermic process) or consumed (endothermic process). The device used for measuring the heat changes in this experiment is called calorimeter. A calorimeter is a Styrofoam cup is used as a calorimeter, because it is a container with good insulated walls to prevent heat exchange with the environment. A strong electrolyte is a solute that completely ionizes or dissociates in a solution. These ions are good conductors of electric current in the solution. All neutralization reactions involving strong electrolytes produces same amount of energy: q = -55.90 kJ of heat per mol of H+. At a constant pressure, the heat of reaction equals the enthalpy change (ΔH); therefore ΔH =-55.90 kJ per mol of H+. The negative sign indicates that the heat is being released and the reaction is exothermic. In contrast to strong electrolytes, weak electrolytes partially ionized in water. The nature of heat of reaction depends on the nature of weak electrolyte and can be either exothermic or endothermic. Thus measurement of heat of reaction will permit to differentiate between strong and weak electrolytes. In this experiment, a weak electrolyte, phenol is used, and the change in enthalpy is endothermic, ΔH=q=25.3kJ/mol. The first part of this experiment involves the neutralization of strong electrolytes. 40 mL of 2.0 M HCL was used to neutralized 50 mL of 2.0 M NaOH. Both the solutions were mixed in the calorimeter and the temperature was recorded after 2 seconds until it reaches maximum, then every 10 seconds for one minutes, and finally every 30 seconds for 3 minutes. Secondly, the neutralization of NaOH with HNO3 was carried out in the same way as described above but instead of using 2.0 M HCL, HNO3 was used and two trials were performed. Furthermore; the neutralization of NaOH with phenol was carried out, and finally neutralization of NaOH with an unknown concentration of HCL solution was carried out and two trials were performed.

Experimental procedure
“The experimental procedure used for this experiment was outlined in the chem. 120L lab manual, Experiment # 4. All steps were followed without deviation”.

Experimental observations (same as data sheet)
Table # 1: change in temperature for every 2 seconds till maximum | 2 sec| 4 sec| 6 sec| 8 sec| 10 sec| 12 sec| 14 sec| 16 sec| Trial 1| 34.0| 35.0| 35.3| 30.0| 33.0| | | |
Trial 2| 30.0| 31.0| 32.0| 33.0| 34.0| | | |
Trial 1| 30.0| 31.0| 32.0| 33.0| 34.0| | | |
Trial 2| 25.0| 27.0| 30.0| 31.0| 32.0| 33.0| 34.0| | Trial 1| 25.0| 25.1| 25.3| 26.0| | | | |
Trial 2| 25.0| 25.5| 26.0| | | | | |
Trial 1| 25.0| 27.0| 30.0| 30.5| 31.0| 31.2| 31.5| 31.8| Trial 2| 25.0| 26.0| 27.0| 30.0| 31.0| 31.5| | |

Table #2: change in temperature for every 10 seconds for 1 minute | 0 sec| 10 sec| 20 sec| 30 sec| 40 sec| 50 sec| 60 sec| Trial 1| 35.0| 35.0| 35.0| 34.9| 34.9| 34.9| 34.9|
Trial 2| 34.5| 34.6| 34.6| 34.6| 34.7| 34.6| 34.6|
Trial 1| 34.0| 34.1| 34.0| 34.0| 34.0| 33.9| 33.9|
Trial 2| 34.5| 34.3| 34.0| 34.0| 34.0| 34.0| 34.0|
Trial 1| 25.5| 25.5| 25.4| 25.4| 25.3| 25.3| 25.3|
Trial 2| 26.0| 26.0| 25.9| 25.9| 25.9| 25.9| 25.9|
Trial 1| 31.8| 31.5| 31.5| 31.4| 31.3| 31.3| 31.2|
Trial 2| 31.7| 31.5| 31.5| 31.2| 31.2| 31.1| 31.1|

Table #3: change in temperature for every 30 seconds for every 3 minutes | 0 sec| 30 sec| 60 sec| 90 sec| 120 sec| 150 sec| 180 sec|...
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