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How do i do this concentration question on absorbance?
What is the concentration of lead in a water sample with an absorbance of A = 0.0068 if a reference sample containing 0.100ppm lead has an absorbance of 0.0165?
Can someone please show me how to work this out.
1 Answer
- 7 years ago
The lower equation should help you here.
If you assume the molar absorptivity (epsilon) is constant, and that the path length (l) is constant, then you can relate the the absorptivity to the concentration.
A=e*l*c
Taking the know concentration sample:
A1 = l * e * C1
A1 = 0.1ppm * l * e = 0.0165
l * e = 0.0165 / 0.1 ppm
l * e = 0.165 ppm^(-1)
This can be applied to the new sample of interest:
A2 = l * e * C2
0.0068 = 0.165ppm^(-1) * C2
C2 = 0.0068 / 0.165 ppm^(-1)
C2 = 0.0412 ppm
Hope that helps, we would indeed expect a lower concentration for less absorption.
Goodluck
