A calibration curve for the colormetric determination of phosphorus
in urine is prepared by reacting standard solutions of phosphate with
molybdenum (IV) and reducing the phosphomolybdic acid complex to
produce the characteristic blue color. The measured absorbance A is
plotted against the concentration of phosphorus. From the following
data, determine the linear least-squares line and calculate the
phosphorus concentration in the urine sample.
a. Use the method of least squares to determine the equation of the line in the form of y=[m(±sm)]x +
[b(±sb)]. Use Excel and do the calculations ‘by hand’. Check your answer using the linest function on
Excel.
b. Construct a graph showing the experimental data and the calculated straight line.
c. An unknown (single sample) gave an observed absorbance of 0.735. Calculate the concentration of
phosphorus and estimate its uncertainty.
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