CHM110H5 Midterm: Pre Lab 4

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Assignment #: 4
Pre Lab
1. Le Chatelier’s Principle states that a sudden change in a
system at equilibrium results in a shift of the equilibrium in
the direction that minimizes the change1 in order to
reestablish equilibrium. The reaction involves ferric ions
reacting with thiocynate ions to produce the complex ion
FeSCN+2. The reaction follows:
[Fe(H20)6]+3(aq) + SCN-(aq)
[Fe(H20)5(SCN)]
+2(aq) + H2O
However, the water may be omitted as it is a constant, and
thus the equation is:
Fe+3(aq) + SCN-(aq)
Fe(SCN)+2(aq).
The limiting reagent used in Part A of the assignment in
respect to the equation above is Fe+3 and will be reacted with
excess SCN+2. The mole ratio of Fe+3 and Fe(SCN)+2 is a 1:1
mole ratio. Therefore, the equilibrium concentration of
Fe(SCN)+2 will be equal to the initial concentration of Fe+3 in
part A solutions.
2. The Beer-Lambert Law is the linear relationship between the
absorbance and concentration of an absorbing species2. The
Beer-Lamber Law is written as:
A=εbc
Where
ε
is the molar absorbant coefficient, b is the path
length, and c is the analyte concentration. The three factors
are:
i. Molar absorbity
ii. Path Length of the solution
iii. Concentration of the solution
The main factor that is focused on the experiment is
concentration of the solution (c) because the purpose of the
experiment is to determine the stability of Fe(SCN)+2.
3. The absorption coefficient of Fe(SCN)+2 is 447nm as this is
the wavelength in which it absorbs most of the light. This
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