Question

3) Benzo(a)pyrene is a very toxic compound routinely monitored in the environment to prevent humans from contamination. A water plant uses an ultraviolet-visible spectrometer to monitor benzo(a)pyrene in water samples. A calibration curve was built with a series of benzo(a)pyrene standards. The following data was obtained: Benzo(a)pyrene Concentration (parts-per-million, ppm) 0.00 0.50 1.00 1.50 2.00 2.50 Fluorescence Intensity (counts) 2.21 x 104 4.50 x 10 8.69 x 10 1.31 x 10 1.85 x 10 1.96 x 10 2.02 x 10 a) Plot the data with Excel. b) Visually, determine the experimental data that fits a straight line. c) Determine the slope and the intercept for the best straight line. d) Calculate the correlation coefficient for the data points that fit a straight line. e) Is it correct to calculate the concentration of benzo(a)pyrene in a sample yielding a fluorescence intensity of 1.98 x 10 counts? Justify your answer. 1) What is the concentration of benzo(a)pyrene in a sample yielding a fluorescence intensity of 7.20 x 10 counts? B) Assume a solution with unknown concentration of benzo(a)pyrene gave a reading of 4.5 x 10" counts. 1.00 ml of this sample was pipetted into a 100 ml volumetric flask. After completing the volume with pure water, the new reading was 7.0 x 10 counts. What is the concentration of benzo(a)pyrene in the original water sample?

Answer 1

Part a) we take the data given, and we filled the excel program with that and then:

ppm vs counts Concentration of Benezeno(a)pyrene (ppm) flourescense intensity (counts) 2,50E+06 2,00E+06 0 0,5 1,50E+06 L 2,21E+04 4,50E+05 8,69E+05 1,31E+06 1,85E+06 1,96E+06 2,02E+06 1,5 2 2,5 3 counts 1,00E+06 • ppm vs counts 5,00E+05 0,00E+00 0 0,5 1 2 ,5 3 3,5 1,5 2 ppm

b) Visually the straight line is:

ppm vs counts 2,50E+06 2,00E+06 1,50E+06 1,00E+06 ppm vs counts 5,00E+05 0,00E+00 O 0,5 1 2 ,5 3 3,5 1,5 2 ppm

so the ppm data at 0, 0.5, 1.0, 1.5 have a continuous behavior, meanwhile to 2.0, and 3.0 are away from the line, and the 2.5 is close to the line, so if we adapt the data:

C) The intercept is the value of the y axis when the value of x is 0, and for the data data taking the ppm as "X" for a value of 0 the y axis has a value of 2.21e+4
b=2.21e+4

Concentration of flourescense Benezeno(a)pyrene intensity (ppm) (counts) O 2,21E+04 0,5 4,50E+05 8,69E+05 1,5 1,31E+06 2,5 1,96E+06

To the slope "m":

m = (Yz – y.) (x2 – X)

Taking the date from the table above to Y2= 8.69e+5, X2=1 , Y1=4.5e+5 and X1=0.5

m = (yz - y.) m = (x2 – XL) (8,69x105 – 4,5x105) Counts (1 – 0,5) ppm Counts m = 8,38x105 ppm

d) Correlation coeficient R:

[(0-1,1) (2,21x10* - 9,22x10') + (0.5 - 11) (4,50x 10- 9,22x10-) + (1 - 11) (8,69x10° - 9,22x10-) +(1.5 - 1.1) (1.31x10 - 9,22x10) + (2.5 -1,1) (1,96x10 - 9,22x10-)] *(C0–1,1))+ (0.5 – 1,1)2 + (1 – 1,1)+ + (1.5 – 1,1)+ +(2,5 – 1,1)(2.21x10* – 9,22x10º)* + (4.50x10* – 9,22x10)+ (8,69x10° – 9,22x10*)* + (1,31x10* – 9,22x10º)* + (1,96x103 – 9,22x10°17) R= 0,9951

e) it is not correct because the data is below the value that is asked, so an extrapolation of this size results in a large error