Question

The following questions are related the this data:
Solutions concentrations in μM Absorbance at 625 nm
Standard 1 2.00 0.065
Standard 2 6.00 0.205
Standard 3 10.00 0.338
Standard 4 14.00 0.474
Standard 5 18.00 0.598
Unknown ? 0.402
a) Plot and label the calibration curve for this data.
b) Assuming the sample is measured in a 1.00-cm cell, show 2 different methods for the determination molar absorptivity of the analyte.
c) Find the blank’s absorbance and the write the equation for this calibration curve.
d) Show 2 different methods for the determination of the concentration of the unknown sample.
e) Calculate %T for standard #3.

Answer 1

Solution.

a) The scatter plot with a linear calibration curve is given below:

b) The molar absorptivity (e) of the analyte can be found from Beer's equation:

According to a second method, the slope of a line A=f(c) is (el):

c) The blank's absorbance is the y-intercept and it equalls to 0.0023. The equation for this calibration curve is

d) The concentration of the unknown sample can be found as

Or using a graph as the second method we will get the same value.

e) Using a formula