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Final

# CHM110 Experiment 5 Report.docx

11 Pages
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School
University of Toronto Mississauga
Department
Chemistry
Course
CHM110H5
Professor
Judith C Poe
Semester
Fall

Description
Purpose: The purpose of this experiment was to measure heats of several reactions and also the enthalpies of neutralization of a strong and a weak acid. To perform the experiment, the system must be effectively insulated from its surroundings. Using a Styrofoam cup, an effective and a suitable calorimeter was made which served as the reaction vessel. The temperature change from a reaction carried out inside the calorimeter can be measured and the change in heat content may be calculated if the total heat capacity of the system (calorimeter and contents) is known. In general, the heat q in Joules can be expressed as (1) where V is the volume in mL, ρ is its density in g/mL, is the specific heat capacity in J/gK, and (= Tfinal Tinitials the change in temperature in K. In the first part of the experiment, the specific heat capacity of the calorimeter is measured and calculated using the formula: |Heat lost by hot water| = |Heat gained by cold water| + |Heat gained by calorimeter| (2) where heat lost by hot water is q h heat lost by cold water is qcand heat gained by calorimeter is After obtaining , the value will be used in obtaining the heats of neutralization of an acid and a strong base. To obtain the heat released by the reaction of either the strong or weak acid with the strong base, the formula below will be used: |Total heat lost| = |Heat absorbed by acid| + |Heat absorbed by base|+ |Heat absorbed by calorimeter| (3) where heat lost by acid is q , heat lost by base is q and heat gained by calorimeter is a b Experimental Method:  Refer to Laboratory manual 2 o No deviations were taken from the Lab manual Results and Calculations: The results of the temperature change when hot water and cold water were mixed are summarized in the following graph. Temperature Vs Time for Hot-Cold water mixture 35 30 °)25 20 15 Temperature ( 5 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Time (s) Figure 1 – The graph summarizes the temperature changes when hot and cold water were mixed together. After extrapolating the linear portion of the data, Extrapolation of Temperature Vs Time for Hot-Cold water mixture 35 30 y = -0.0895x + 31.241 °) 25 R² = 0.9264 20 15 10 Temperature ( 5 0 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 Time (s) Figure 2 – Results of extrapolation of Figure 1. The graph shows the decrease in temperature over time and the rate at which the temperature decreases was found from the slope value (-0.0895 °C/s) From Figure 2, it can was found that the temperature of the mixture was slowly decreasing over time. This shows that the calorimeter was not a perfect insulator and heat was lost to the outside environment. This shows that the Styrofoam cups used during the experiment were not an effective insulator. To calculate the Heat Capacity of the Calorimeter: | | | | | | ( ) ( ) ( ) | | | | | | | | ⁄ ⁄ ⁄ ⁄ ( ) ( ) Heats of Neutralization Neutralization of a Strong Acid and a Strong Base Data from Table A1.2 was plotted to give the following graph Temperature Vs Time for Strong Acid (HCl) - Strong Base (NaOH) reaction mixture 35 30 C25 ° 20 15 Temperature ( 5 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Time (s) Figure 3 - The above graph summarizes the temperature changes when a neutralization reaction between a strong acid (HCl) and Strong base (NaOH) was performed. By extrapolating the data from Figure 3, Extrapolation of Temperature Vs Time for Strong Acid-Strong Base mixture 35 30 °) 25 y = -0.09x + 28.646 R² = 0.9013 20 15 Temperature ( 10 5 0 -2 -1 0 1 2 3 4 5 Time (s) Figure 4 – Results of extrapolation of Figure 3. The above graph factors in the loss of heat by the calorimeter and gives the equilibrium temperature of the reaction mixture. To calculate the q pvolved To calculated the number of moles of acid and base neutralized in the reaction: From the Litmus paper test, it was found that the solution at equilibrium was acidic. This means that the Strong Base that was added to the mixture was the limiting reagent. Thus, Therefore, | | | | [ ] [ ] (Negative since the reaction is exothermic) Literature value of enthalpy of neutralization reaction of a strong acid-strong base = -57.35 KJ/mol | | Therefore, the experimental results have a 14.3% deviation from the literature value. 3) Using the semi-exact simultaneous equation method and assuming [ ] [ ] [ ] [ ] [ ] [ ] | | Since the deviation is significant, the literature value of Dichloro-acetic acid will be used for further calculations. { } { } Question 3 Part B Temperature Vs Time for Weak acid (C H Cl O ) 2 2 2 2 - Strong base (NaOH) reaction 40 °) 30 20 10 Temperature ( 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Time (s) Figure 5 – The above graph summarizes the data for weak acid – strong base reaction Extrapolation of Temperature Vs Time for Weak acid (Dichloro-acetic acid) 40 °) 30 20 y = -0.0774x + 29.456 10 R² = 0.8832 Temperature ( 0 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 Time (s) Figure 6 – By extrapolating the data from figure 5, the above graph was made. It shows that the final temperature achieved through the neutralization reaction was 29.5°C | ⁄ | | ⁄ | | | (
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