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31
Laboratory 5 Report
Name(s):
_____________________________________________________________________
Data Table 5.1 Copper Sulfate Known Dilutions
Dilution
Concentration of
CuSO
4
(M)
Absorbency Value
of CuSO
4
Color of CuSO
4
(Scale 1-5:
1 = lightest, 5 = darkest)
N/A (Distilled H
2
O)
1 in 5
1 in 10
1 in 50
1 in 100
Procedure B: Determination of Copper Sulfate Unknowns
Determine the absorbency values for each one of the unknown copper sulfate solutions labeled A-F using
the spectrophotometer. Record this data in Data Table 5.2 and generate a standard curve on the next page
to determine the concentration by graph method. A second method for calculating an unknown’s
concentration is based on using an equation called the
least squares fit analysis
. This can be done on a
computer with a mathematical algorithm. Your professor will direct you to a computer with this
spreadsheet.
Data Table 5.2 Copper Sulfate Unknowns
Unknown
Absorbency
Value
Concentration
by Graph
Method (M)
Concentration
by Least
Squares (M)
Color of CuSO
4
(Scale 1-6:
1 = lightest, 6 = darkest)
A
B
C
D
E
F
32
Spectrophotometry Graph Analysis:
Generate a graph using the known concentration data from Data
Table 5.1. Plot the absorbency value (Y-axis) against concentration (X-axis) on Figure 5.2. Make note
of the largest absorbance value of your unknowns in order to scale your axis accordingly since this graph
will be used to determine the unknown concentrations from Data Table 5.2. Draw the best fit line through
your known data points. While the data points should fall on a single straight line, it does not have to go
through every data point plotted (Figure 5.1).
Figure 5.1:
Sample
Standardization Graph
(Generate your own graph below)
Figure 5.2: Standardization Graph for Copper Sulfate
33
Observations and Analysis
Write a discussion analyzing the data collected. In your discussion indicate what your concentrations
were and how the two different methods of concentration calculation (graph method and least squares)
compared to each other. Analyze the relationship between color, concentrations, and absorbance.
Your preview ends here
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34
The
distilled
water
concentration
and
absorbency
value
for
procedure
A
were
both
0.
This
suggests
that
of
the
five
solutions,
distilled
water
was
the
lightest.
The
dilution
ratio
for
the
initial
copper
sulfate
solution
was
1
in
5.
In
other
words,
its
concentration
was
0.2
M.
The
absorbance
value
of
this
0.2
M
copper
sulfate
solution
was
1.701,
making
it
the
darkest
of
the
five
solutions.
The
following
copper
sulfate
solution
had
an
absorbency
value
of
0.724
and
a
concentration
of
0.1
M,
or
a
dilution
factor
of
1
in
10.
The
third
copper
sulfate
solution
was
0.02
M
in
concentration,
or
a
dilution
factor
of
1
in
50,
and
had
an
absorbency
value
of
0.135.
The
dilution
factor
of
the
final
copper
sulfate
solution
was
1
in
100.
This
final
solution
was
0.01
M
in
concentration
and
0.065
in
absorbency.
Color,
concentration,
and
absorbance
values
are
closely
related
to
one
another
because
when
one
increases,
so
do
the
others.
We
recorded
the
absorbency
values
of
all
six
unknowns
for
process
B
and
then
assessed
their
color
on
a
scale
of
1-6.
Where
1
represents
the
lightest
and
6
represents
the
darkest.
Unknown
A
had
a
color
rating
of
2
and
an
absorbency
value
of
0.349.
Second,
unknown
B
had
a
color
rating
of
3
and
an
absorbency
value
of
0.182.
Third,
unknown
C
had
a
color
rating
of
5
and
an
absorbency
value
of
0.715.After
that,
unknown
D
had
an
absorbency
value
of
0.107
and
a
color
grade
of
1,
indicating
that
it
was
the
darkest
copper
sulfate
solution.
Then
there
was
unknown
E,
with
an
absorbency
of
1.156.
Because
of
its
high
absorbency
value,
unknown
E
has
the
darkest
copper
sulfate
solution,
giving
it
a
color
grade
of
6.
Lastly,
unknown
F
got
a
color
rating
of
4
and
an
absorbency
value
of
0.528.
After
determining
the
absorbency
values,
we
used
two
approaches
to
calculate
the
concentrations.
The
initial
approach
was
the
least
squares
concentration.The
instructor's
Computer
was
running
a
special
excel
software
that
vomited
out
the
concentration
data.
The
data
from
method
A
was
then
graphed.
The
x-axis
represents
molar
concentration,
while
the
y-axis
represents
absorbency
at
690
nm.
After
graphing
the
points,
we
constructed
the
best-representing
trend
line.
We
looked
at
the
absorbance
value
and
then
where
that
value
intersected
the
trend
line
to
determine
the
amounts
of
the
unknowns.
The
x-axis
value
is
determined
by
where
the
absorbance
value
intersects
the
trend
line.
Because
the
x-axis
depicts
molar
concentration,
we
recorded
the
concentration
values
using
our
best
guess.The
graph
technique
yielded
a
concentration
value
of
0.045
M
for
unknown
A,
whereas
the
least
squares
approach
yielded
a
concentration
value
of
0.046
M.
Second,
for
unknown
B,
the
graph
technique
yielded
a
concentration
of
0.025
M,
but
the
least
squares
method
yielded
0.026
M.
Finally,
for
unknown
C,
the
graph
technique
yielded
a
concentration
of
0.09
M,
but
the
least
squares
method
yielded
0.089
M.
The
graph
technique
produced
a
concentration
value
of
0.015
M
for
unknown
D,
whereas
the
least
squares
approach
produced
a
concentration
value
of
0.017
M.
The
graph
approach
then
gave
us
a
concentration
value
of
0.145
M
for
unknown
E,
whereas
the
least
squares
method
gave
us
0.0141
M.
Eventually,
for
unknown
F,
the
graph
approach
yielded
a
concentration
value
of
0.067
M,
whereas
the
least
squares
technique
yielded
a
concentration
value
of
0.067
M.
Generally,
the
concentration
differences
between
the
graph
and
least
squares
approaches
were
minor.
The
greatest
concentration
disparity
was
for
unknown
E.
The
graph
technique
yielded
a
value
of
0.145
M,
whereas
the
least
squares
yielded
a
value
of
0.141
M.
The
overall
difference
was
0.004
M.
While
0.004
M
is
a
modest
variation
and
the
greatest
difference
between
the
two
procedures,
I
would
suggest
that
these
methods
provide
similar
outcomes.
Otherwise,
the
approaches
produced
fairly
comparable
results,
and
one
even
produced
an
exact
number
for
the
unknown
F.Procedure
B,
like
Procedure
A,
leads
to
the
conclusion
that
color,
concentration,
and
absorbance
values
are
directly
proportionate
to
one
another.
We
may
draw
this
conclusion
because
when
one
of
these
variables
grew,
so
did
the
others.
The
solution
with
the
darkest
hue,
unknown
E,
had
the
highest
concentration
and
absorbency
value.
Although
unknown
D
was
the
lightest
in
color,
concentration,
and
absorbency
rating.
When
the
concentration
grows,
so
does
the
absorbency
value,
and
the
color
becomes
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