A calibration curve constructed from absorbance values of solutions containing a
ID: 524121 • Letter: A
Question
A calibration curve constructed from absorbance values of solutions containing a known concentration of permanganate ions has the following best-fit line:
y = (3.62 × 103 L/mol) x
where y is the absorbance of the solution at 525 nm and x is the concentration of MnO4– (aq) in mol/L. The pathlength of the cuvettes used in the experiment is 1 cm. Based on this information, what is the molar absorptivity of MnO4– (aq) at 525 nm? Be sure to include units in your answer.
Molar absorptivity of MnO4– (aq) at 525 nm: __________________________
A sample of steel weighing 0.1863 g was dissolved and the manganese present was converted to MnO4– (aq). Water was then added to give a final solution volume of 100.00 mL. A sample of this solution was examined and was found to have an absorbance at 525 nm of 0.620 (pathlength = 1 cm). What is the percent Mn in this sample of steel?
Explanation / Answer
According to Beer Lambert's law, Absorbance, A= eCl
Where e is the molar absorptivity
C is the concentration and l is the path length.
Hence comparing this with equation of line,
e= 3.62*10^3 L/ mol cm
B)Using the equation
0.62= 3.62*10^3 * C
Therefore C= 0.62/3.62 *10^3= 1.74*10^ -4 M
# moles of Mn = 1.74*10^-4*100=0.0174 mmoles
Mass of Mn = 0.0174*54.93= 0.956 mg
% of Mn = 0.956*10^-3*100/0.1863= 0.513%
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.