The determination of iron in industrial waste stream is often carried out by reacting the water sample with o-phenanthroline to form a red-orange complex that absorbs at 510 nm

CREATION OF A STANDARD CURVE AND DETERMINATION OF AN UNKNOWN SAMPLE

ABSORBANCE AND BEER'S LAW

Here is a straight forward approach to solving the problem. Please see the Excel file for the data work up. Nevertheless, you should practice doing it on your own so that you learn how.

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Step 1: The first thing you do is transfer the data to an Excel file.

Step 2: Highlight all of the data.

Step 3: Click on Chart Wizard

Step 4: Choose Graph Type: XY (Scatter)

Step 5: Once you've got the graph, you will notice that there is no line. Therefore, you need to add a trendline.

Step 6: Click on a data point, then right click to get the drop down menu. Choose Add Trendline.

Step 7: Choose Linear Type Regression line.

Step 8: Go to Options and select Set Intercept = 0

Step 9: Also, select Display Equation on Chart.

Step 10: Click OK

Step 11: Now, you've got the actual standard calibration curve. Looks nice, eh?

Step 12: Finally, we must determine the concentration (in ppm) of the sample. Contrary to what you have written in the data table, 5.0 ppm does not equal 0.269 absorbance units. This appears to be the sample. It's not 5.0 ppm. We must determine the concentration using the equation from the trendline.

Step 13: y = 0.1819x is the equation for the trendline. We know "y" and we must determine "x".

Step 14: 0.269 = 0.1819x

Step 15: Solve for x

Step 16: x = 1.5 ppm

Conclusion: The concentration of iron in the waste stream is 1.5 ppm.

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