These concentrations were compared against the average absorbance in the four
plots illustrated in the results section. According to Beer’s Law, the slope of each of the
lines shown is equivalent to the
k
constant for each standard at each wavelength. These
constants were found to be .001500 for manganese at 440nm and .0283 for manganese at
545nm. The chromium ion was calculated to have a
k
value of .003700 at 440nm and .
00009000 at 545nm.
The absorbance of the unknown at each of the wavelengths was taken for three
different trials, for trials one, two, and three, the absorbance of the unknown at 440nm
was recorded as .51. In trial one, the absorbance at 545nm was calculated to be .273, and
to be .26 for trials two and three. Using these values, along with the
k
values derived from
each of the linear functions, the concentration of each ion was found. The concentration
of Mn in trials two and three was calculated as 8.76 mg/L , and 9.22 mg/L for trial one,
giving an average of 8.913 mg/L. In trials two and three, the concentration of chromium
deduced to be 134.3 mg/L, and 134.1 mg/L for trial one, giving an average of 134.2
11

mg/L.
The standard deviation for manganese was .2656, giving a relative standard
deviation of 2.98%. The standard deviation for chromium was .1074, resulting in a
relative standard deviation of .08%.
Conclusions & Recommendations
The results analyzed in the discussion prove the hypothesis to only be partly true.
The relative standard deviation for the manganese ion was 2.48% greater than
hypothesized, while the relative standard deviation for the chromium ion was .42% lower
than hypothesized. Relative standard deviation is used to measure precision by
illustrating the percent difference between the data and the mean. The calculated relative
standard deviations suggest that the data for the manganese concentration varied almost
six times more than the data did for the chromium concentration. Despite this difference
in RSD, the low percentages suggest that the experiment is most likely repeatable.
An extremely significant gross error occurred while performing this experiment,
preventing any real comparison an accepted value from taking place. The wrong
concentration of H
2
SO
4
was used to dilute the samples, while the correct concentration
was used for the blank solution. This discrepancy resulted in a spectrophotometer that
was incorrectly calibrated, and solutions that were far too concentrated. As previously
mentioned, this is a gross error, and in analytical analysis, gross errors require the
experiment to be scratched, and for the procedure to be restarted.
Aside from eliminating gross error, a number of changes to the procedure and
materials used in the experiment could lead to more accurate results. The cuvettes used in
this experiment were made of plastic. Glass cuvettes have been found to give more
12