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Suppose an unknown sample has an absorbance which is significantly larger than t

ID: 914646 • Letter: S

Question

Suppose an unknown sample has an absorbance which is significantly larger than the absorbance of the most concentrated standard and so is outside the range of the calibration curve. What should the analyst do to accurately determine the concentration for the unknown using Beers law? Extending the calibration curve or using the equation for the line are not correct answers to this question. Suppose an unknown sample has an absorbance which is significantly larger than the absorbance of the most concentrated standard and so is outside the range of the calibration curve. What should the analyst do to accurately determine the concentration for the unknown using Beers law? Extending the calibration curve or using the equation for the line are not correct answers to this question.

Explanation / Answer

Let C be the molar concentration of the unknown sample.

Dilute the unknown sample 10 times by using standard volumetric flask. Since absorbance is directly proportional to molar concentration, new absorbance will be one tength of original absorbance. If new absorbance is within the range of the calibration curve, we can now measure it. However if the new absorbance is still outside the range of calibration curve, then we can continue dilution till it is within the range of calibration curve. Now we can determine the concentration of diluted sample from which, we can calculate the concentration of original sample.

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