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Lecture 3

CHM 1311 Lecture Notes - Lecture 3: Rate Equation, Chemical Kinetics, Ethylenediaminetetraacetic Acid


Department
Chemistry
Course Code
CHM 1311
Professor
Wendy Pell
Lecture
3

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Student Name: Colin Flamminio
Student Number: 8300297
Partner’s Name and Student #: Brad Austin - 8121944
Demonstrator's Name: Puneet Labana
PLEASE NOTE: If ANY of the above information is UNCLEAR or not provided, your grade
will NOT be recorded!!
Lab Day (circle): Tues Wed Thurs Fri
Time slot (circle): morning afternoon night
Lab Week (circle): 1 2
Laboratory Report Cover Page
Experiment 3.
Chemical Kinetics
Checklist:
oRaw Data Sheet copy attached
o9 curves [3 for A vs t; 3 for log A vs t; 3
for log Rate vs log A] attached
oCompleted formal report typed and attached
Student’s Initials: CF

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Introduction:
This experiment covered concepts for chemical kinetics involving concentrations using a
spectrometer to measure absorbance over time while ions dissociate.
Chemical kinetics is the study of the rates of reactions based on concentrations and
temperatures. Basically, the higher the concentration is, the faster the reaction occurs. This
does not affect the yield. This experiment specifically covers how the rate of the reaction is
affected by the concentration of reactants, also known as the order of the reaction.
The rate of a reaction is dependent on multiple factors and is directly proportional to
the concentration and the rate constant of a reaction. It can be expressed by:
Rate = k [A]n[B]m[1]
Where [A] and [B] are the concentrations expressed in moles per liter, and k is
dependent on the orders(superscript n and m) of the reaction.
The rate can also be determined with graphical means using experimental data for
concentrations versus time. Rate at a specific time is equivalent to the instantaneous velocity
on the graph of concentrations versus time. The orders of specific ions can also be determined
using the integrated rate laws. Orders can be differentiated by determining the linearity of a
graph of the concentration vs time(representing zero order), log concentration vs.
time(representing first order), and inverse concentration vs. time(representing second order).
For example if a concentration is first order in a specific reaction, it would be linear when
looking at the graph of its log concentration vs. time:
Figure 1:
The order of a reaction can only be determined graphically. Similar to Figure 1, the
graph of log[ACrIII] should have a linear fit, and we should witness pseudo first-order kinetics.
The reaction rate is also unaffected by the EDTA solution used to react with the Cr(III)
because the concentration of the EDTA is kept fairly high compared to the Cr(III), so it is
negligible. This is important because if both concentrations were changing it would be
impossible to measure the change in concentration and order of the Cr(III).
This lab utilizes the science of spectrometry, which is a chemistry technique that helps
identify the amount and type of chemicals present in a sample. In this lab a spectrometer will
be used to determine the absorbance of a specific chemical. This absorbance is directly
proportional to the concentration and will actually be representative of the concentration for
quantitative purposes.

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Procedure:
As outlined in the manual
Data:
Table 1: Raw Data:
Trial 1 Trial 2 Trial 3
Max Absorbance 1.801 @ 556.50 nm 1.801 @ 556.50 nm 1.801 @ 556.50 nm
pH of Solution 4.0 4.5 5.0
Volume of Solution 10mL 10mL 10mL
Total time elapsed 42 min 32 min 32 min
Absorbance after
40/30 minutes
0.371 0.423 0.736
A1.679 1.926 2.115
Observations:
Trial 1:
- Absorption rising as reaction continues.
Trial 2:
EDTA Solution and Chromium Ions seems thicker – Higher concentration of Cr(III) Ions.
Absorption rising faster than first trial
Trial 3:
pH solution darker again
higher initial increase in absorption
Reacting faster becasue higher EDTA concentration.
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