8. [Intro. analytical chemistry] - please solve and show work / and explanations

Question

8. [Intro. analytical chemistry] - please solve and show work / and explanations: (if the process towards the answer would be obscure without one) and include uncertainty in answers if applicable. Only the supplemental data provided below the questions should be used in the answers (if needed at all). If there is not enough information to complete the problem please let me know.

8. 8 points] In an atomic absorption experiment, the chromium in an aqueous sample was determined by the standard addition method. A plot of the results, along with the least squares fit, is shown at right. What is the concentration of chromium in the unknown sample? 0.6 0.5 E 0.4 0.3 0.2 K 0.1 y 0.0361x 0.2022 R2 0.99993 10 Cr added (ppm)

Explanation / Answer

The unknown concentration in the sample is obtained by setting the instrument response (y-intercept) as zero. Thus, we have,

0 = 0.0361x + 0.2022

===> x = -(0.2022/0.0361)

We must ignore the negative sign (since concentration cannot be negative). Therefore, x = 5.601 5.60

The unknown concentration is 5.60 ppm.

(I have calculated simply on the basis of the data provided; for a more rigorous treatment, volume of the unknown solution, volume of the standard solution, etc will be needed).

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