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CHM-120-Experiment 5 report.docx
CHM-120-Experiment 5 report.docx

CHM-120-Experiment 5 report.docx

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University of Toronto Mississauga

Chemistry

CHM120H5

Judith C Poe

Winter

Description

P a g e | 1
Introduction:
The purpose of the experiment was to find the rate constant and the activation energy of reaction
between a bidentate ligand, 1,10-phenanthroline and ferrous ions in an acidic solution which forms a
iron (II) cation.
When 1,10-phenanthroline is present in acid, its dibasic property allows it to act as a base and it gets is
protonated.
Also, Arrhenius equation was used in calculating the activation energy where ‘k’ is the rate constant, A
is the pre-exponential factor or the frequency factor, EA is the activation energy, R is the universal gas
constant and T is the Kelvin temperature.
Activation energy is the minimum energy that must be input to a chemical system, containing potential
reactants, in order for a chemical reaction to occur. The rate of a reaction, which is directly related to
the activation energy, can be defined as the change in concentration of the reactants and products
over time and when the concentration of the reactants is reduced by half of its initial concentration; it
is termed as the half-life of the compound.
Experimental Method:
1
Refer to Lab Manual P a g e | 2
Collection of data:
Refer to the attached data sheet
Results and Calculation:
P ART A – D ETERMINING THE RATE CONSTANT AT 30°C
Table – 1: Calculations from experimental data
Time (seconds) Optical Density
Time (min) (1 min = 60 seconds) (at 510 nm)
11.58 694.8 1.07 0.0677
21.54 1292.4 0.953 -0.0481
30.3 1818 0.838 -0.177
43.39 2603.4 0.753 -0.284
51.09 3065.4 0.69 -0.371
62.1 3726 0.6 -0.511
71.23 4273.8 0.555 -0.589
81.01 4860.6 0.48 -0.734
92.04 5522.4 0.426 -0.853
102.49 6149.4 0.379 -0.970
120.29 7217.4 0.325 -1.124
Rate constant at 30°C
0.2
0
-0.2 0 1000 2000 3000 4000 5000 6000 7000 8000
-0.4
-0.6
ln O.D y = -0.000185x + 0.1862
-0.8
R² = 0.9979
-1
-1.2
-1.4
Time (s)
Figure – 1: The above graph represents the relation between ln O.D and time where ln O.D is
dependent on time. The slope of the graph represents the –k in the following derivation which is
essentially the rate constant of the reaction P a g e | 3
The rate law for the overall reaction observed in this experiment can be written as
[ ]
[ ]
Integrating both sides of the equation, the following is obtained
[ ] [ ]
∫ ∫
[ ] [ ]
[ ] [ ]
The rate constant can then be determined using the integrated first-order rate law which states that
[ ] [ ]
The concentration of can be related to the measured absorbance through the beer lambert law.
[ ]
where O.D is the optical density (absorbance), [Fe] is concentration of the solute in mol/L, b is the path
length of the sample in cm, and is the molar extinction coefficient in L/mol cm. By rearranging the
equation, [Fe] can be expressed as
[ ]
Replacing [Fe] in the integrated rate law, the following is obtained
Rearranging this: P a g e | 4
Therefore, which represent an equation of a line and by taking the slope of the
-4 -1
line of best fit, the rate constant of the reaction is found to be 1.85 x 10 Sec .
P ART B – D ETERMINING THE ACTIVATION ENERGY
The rate constant of a chemical reaction can be found by applying Arrhenius equation
By taking natural logarithm on both sides,
This equation is of the form Y = mX + B where Y represents and X represents . The slope ‘m’ is
equal to and is the y-intercept, B.
In order to find the value of K, the half-life timings that were recorded during the experiment were
used.
[ ]and it can also be written as a rate law [ ]
By equating those two equat

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