Lab ppm Question help

Question

Hi, guys in a lab report about Iron and its calibration curve I am supposed to solve for the ppm of Fe in a standard solution. My data in the chart says that the ppm should equal 1.04.

I'm supposed to use the calibration graph which has a slope of 0.2249 and an intercept of 0.0169. Where the y-axis is absorbance and the x-axis is ppm. I plugged in the correlated absorbance as y to solve for x and keep getting a different answer that is not even close to 1.04.

For reference:

Conc of Fe standard = 259.7ppm

standard vol flask = 50.0ml

the trial I am supposed to use has 200 microliters, 1.04 ppm, an absorbance of 0.299, and a correlated absorbance of 0.278.

If anyone has any idea on how to go about this I would appreciate it! I mentioned I have tried to plug both absorbances as y in the y=mx+b equation and have not gotten 1.04ppm

Answer 1

I read your original question on the same problem, but here you added more information. It is so important that when you pose a question on this forum, you include ALL relative information. Here is where the 1.04 ppm comes from...

If you take 200 ul of the standard Fe solution and dilute it to 50.0 ml, that represents a 250-fold dilution (50 ml / 0.2 ml = 250). Since the original Fe solution was 259.7 ppm, the diluted solution will be 259.7 ppm / 250 = 1.04 ppm.

That's it. Don't have to use the linear regression equation or any other information. This is simply a dilution problem. If you want to estimate the absorbance of this sample, then you can substitute 1.04 as x and solve for y.

Does this make sense to you?