Predicting the concentration without doing any calculations

Question

I’m very confused on this question.

5 marks

You and Noel, your lab partner, had used the Beer-Lambert Law to calculate the concentration of light-absorbing solute, knowing its molar extinction coefficient and its measured absorbable in a 1 cm cuvette. You found the solution was 100 µM.

You were given another 1cm cuvette, containing the same light absorbing substance. The absorbance value obtained for this sample was 1/10th of that obtained from the first sample.

You immediately predicted the correct concentration, even without doing any calculations. But Noel was baffled!

Remind Noel of the PREDICTED CONCETRATION AND BRIEFLY EXPLAIN to him how you arrived at this estimate

Answer 1

The Beer-Lambert Law essentially says that the absorbance in a 1 cm path is equal to the molar extinction coefficient times the concentration. It is written as A =elc where A=absorbance; e=extinction coefficient; l=path length(1cm) and c=concentration.

From this relationship you can see that the concentration is directly proportional to the absorbance and related by the extinction coefficient. So, if the absorbance of the new sample is 1/10th that of the first sample, the concentration of the new sample would be 1/10 that of the original or 10 uM.