5. A calibration curve for the colormetric determination of phosphorus in urine

Question

5. A calibration curve for the colormetric determination of phosphorus in urine is prepared by reacting standard solutions of phosphate with molybdenum (V) 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. 0.214 0.536 0.843 1.267 Urine sample0.735 m P Absorbance 1.00 2.00 3.00 4.00 Use the method of least squares to determine the equation of the line in the form of y-[m(tsmlx+[b(tsol]. Show your calculations and check your answer using the linest function on Excel. a. b. Attach a graph showing the experimental data and the calculated straight line. An unknown (single sample) gave an observed absorbance of 0.735. Calculate the concentration of phosphorus and estimate its uncertainty. c.

Explanation / Answer

the plot of concentration (ppm) vs absorbance is straight line. This is drawn ( except for the last data point ) and shown below.

from the plot, the equation of best fit is Absorbance= 0.3466* concentration (ppm)-0.1515

when A=0.735, concentration = (0.735+0.1515)/0.3466=2.56ppm

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