SUPL004 – Problems
1. The following data are collected in an experiment in which the absorption of
light at a wavelength of 535 nm by solutions of various concentrations of iron(II)
sulfate in water is measured. Assume that the concentration of iron(II) sulfate is
the independent variable and that it is measured in moles/Liter. The dependent
variable, the absorbance of the solution at light of wavelength 535 nm, has no
units.
CONCENTRATION 0.000
0.001
0.002
0.005
0.010
0.020
0.030
0.050
ABSORBANCE
0.00
0.04
0.08
0.19
0.35
0.79
1.10
1.85
a. What will be the values of concentration and absorbance at the origin of the
graph?
The origin of the graph will be at the point (0.000,0.000)
b. What are the ranges of the concentration and absorbance measurements?
The range of concentration is 0 – 0.05 mol / L
The range of absorbance is 0 – 1.85
c. Which variable will be plotted as the abscissa (xaxis)?
It is traditional to display the independent variable on the abscissa.
Therefore, the x
axis will display the concentration.
d. Assuming graph paper with a grid of 1 mm × 1 mm boxes, with dimensions
180 mm × 250 mm, what should you chose for the number of boxes per unit
for concentration? For absorbance?
Since the range of absorbance is 1.85, we would not be able to include the last point of
the data if we use 1 cm for 1 unit of Absorbance.
We also cannot use 1 cm for 1 unit
of concentration along the 180 mm axis for the same reason.
We will need to use 1 cm for at least 2 units of either absorbance or concentration.
Suppose we use 1 cm for 2 units of Absorbance.
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 Spring '09
 RALEIGH
 Chemistry, Orders of magnitude, red line, Ferrous Sulfate Solutions vs Concentration

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