Determining The Unknown Concentration Of Neutralization Of Hcl By

Determining the unknown concentration of HCl via heat of neutralization of a reaction involving strong electrolytes and weak electrolytes.
Myeongwon Lee
20522885
Partner: Frank Wong
TA: Afsoon
CHEM 120L – Earth Science & Chem 149 Section: 004
Tuesday, November 26th, 2013
Introduction
All chemical changes are accompanied by change in energy and this energy is in form of heat. The energy change of a reaction that happens at constant pressure is defined as heat of reaction or enthalpy change and the symbol ∆H is used to denote the enthalpy change. The enthalpy change can be either endothermic or exothermic. In endothermic reaction, ∆H > 0, meaning heat is absorbed by the system from the surrounding. In exothermic reaction, ∆H < 0,
Strong electrolytes such as NaOH, HCl, and HNO3 completely dissociate into its component ions in aqueous solutions where else weak electrolytes such as phenol only partially dissociates into ions in aqueous solutions. (Daintith, 2010).
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 (Dept. of Chemistry, 2013).

Experimental Observation
Part A: Neutralization of NaOH with HCL
Concentrations
[HCl] =1.778M
[NaOH] =2.075M
Trial 1 Initial Temperature
HCl =21.0⁰C
NaOH =21.5⁰C
Trial 2 Initial Temperature
HCl =21.0⁰C
NaOH =21.5⁰C
Table 1. Data obtained from Part A of the experiment.
Part B: Neutralization of NaOH with HNO3
Concentrations
[HNO3] =1.778M
[NaOH] =2.075M
Trial 1 Initial Temperature
HNO3=21.0⁰C
NaOH =21.0⁰C
Trial 2 Initial Temperature
HNO3=20.5⁰C
NaOH =21.0⁰C Table 2. Data obtained from Part B of the experiment.
Part C: Neutralization of NaOH with Phenol
Concentrations
[Phenol] =0.5115M
[NaOH]
In order to do this, four different but relatively similar procedures Part A, Part B, Part C, and Part D were conducted. In Part A, 50mL of 2.075M NaOH and 40mL of 1.778M HCl were obtained and both of this acid and base initial room temperature was measured. The temperature of the acid was adjusted so that it had the same temperature of the base within 0.5⁰C. Next, the entire 40mL of HCl and 50mL of NaOH were poured into the coffee cup calorimeter with the lid on top of the cup and the thermometer in place. The enthalpy change was detected by using the thermometer which was inserted in a coffee cup calorimeter. Using the thermometer, the change in temperature of the reaction with respect to time was recorded. Part B, Part C, and Part D were carried out in same procedure but neutralization of different acids with NaOH. Part B dealt with neutralization of NaOH with HNO3, Part C dealt with neutralization of NaOH with phenol, and Part D dealt with neutralization of NaOH with unknown concentration of HCl. A total of two trials for each part were conducted and a temperature vs. time graph was plotted for each trial. From the experiment, the neutralization reactions involving strong and weak electrolytes for Part A produced q=-51.359kJ of heat per mole of H+ and Part B produced q= -52.097 kJ of heat per mole of H+. Theses