Use the following table of standard concentrations and absorbances for the phosp
ID: 1001351 • Letter: U
Question
Use the following table of standard concentrations and absorbances for the phosphate ion to create a calibration graph. What are the slope and intercept of the calibration curve? What is the concentration of phosphate in a solution that has an absorbance of 0.708 AU? One of your samples shows a reading of 1.541 AU, which is beyond the range of the calibration curve. The lab is over and it is too late to redo the calibration over a broader range, or to dilute the sample and determine it a second time. Assume that Beer's Law still holds up to the value of the sample, and calculate the concentration using the equation for the calibration line. (Path length = 1.0 cm)Explanation / Answer
The calibration curve can be plotted as below:
This curve is of the form y = mx + c where m = slope of the curve and c = intercept. From the curve, m = 0.0937 and c = 0.0737 (ans)
In this part, y = 0.708 AU and we need to find x (concentration). Therefore,
0.708 = 0.0937x + 0.0737
===> 0.0937x = 0.6343
===> x = 6.769
The unknown concentration is 6.769 ppm 6.77 ppm (ans)
In this part of the problem, we have y = 1.541 AU (we are supposed to use the calibration curve).
Therefore,
1.541 = 0.0937x + 0.0737
===> 0.0937x = 1.4673
===> x = 15.659
The unknown concentration is 15.659 ppm 15.66 ppm (ans)
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