[formulations4me]

I have worked through the problem a multitude of times, and am unable to get the right answer. Any help would be appreciated. Thanks.

Cu does not absorb strongly in the visible, but a colored product containing only 1 mole Cu/mol product does. A series of Cu standards was prepared by mixing color developing reagents with different volumes of a stock Cu standard to form the product before diluting to volume in volumetric flasks. In a 3-cm cell, a graph of absorbance, A, vs concentration of Cu in µg Cu/mL gave a straight line calibration curve. The data were fit to a straight line:

A = a b C + Ablank
A = E*b*C, e= molecular absorption, b= cell size, and c = concentration.

The results of the Excel linest function are given below.


0.5707 -0.0760
0.001382 0.0433
0.99376 0.01810
x 7
x x

1) Calculate the 95 % confidence limit in the absorbance of the blank.
2) Calculate the molar absorptivity of the product in cm2/mmol Cu. a. w. Cu = 63.5

[Golden_4_Life]

Pls post up a compendium of your ss data because as it is currently written, it is indecipherable to us thanks

[einsteinium]

Hey I have this same exact question and I can't figure it out either... at least not the second part.

For the first part (the 95% CL in the absorption of the blank, Ablank) you just take the tinv(0.05,df)*Sao where Sao is the standard error in the y-intercept, which is in your case 0.0433..

Could somebody please explain how to do the second part though???  I know it involves converting the slope into the correct units but I tried:
slope (mL/ug) x 63.5mg x 1000ug x 1
                       1mmol      1mg     5cm

Actually, I think I hadn't inversed the units for the slope as this looks correct... I think I tried dividing by 1000 instead of multiplying.  Can somebody please check my work..  the expression above should yield an answer in the units of cm^2/mmol correct?  And then for the 95% CL I would just take the s of the slope and multiply it by the same constants as above...

Oh and to Golden_4_Life, the poster has correctly supplied all necessary information (exactly as it was asked).