The absorbance at 470 nm of the Fe(ll) phenanthroline complex was measured for s

ID: 486566 • Letter: T

Question

The absorbance at 470 nm of the Fe(ll) phenanthroline complex was measured for several different Fe2 concentrations in order to create a calibration curve. The absorbance at each Fe concentration was measured five times. The readings, already corrected for the blank solutions, are shown below 75.9 0.582 0.591 0.587 0.583 0.588 .5862 .0585 919.6 0.412 0.411 0.421 0.414 0.418 .4152 0050 62.8 53.5 37.7 0.264 0.266 0.269 0.258 0.266 .2646 0063 62.0 15.2 0.109 0.113 0.108 0.115 0.111 .1112 .0543 922.6 182.3 1.367 1.381 1.385 1.370 1.383 1.377 1242 1967 sum average 45.575 0.3418 0.345 0.346 0.343 0.346 .3443 Number (a) Use the averages of the replicate absorbance AIM-1 measurements to determine the slope and y-intercept of the best-fit straight line. Number b- (b) Predict the Fe2 Number concentration in an unknown sample that LIM has an absorbance of 0.129.

Explanation / Answer

(a) Prepare the following table using the mean of the absorbance of the six different concentrations.

Average yi

[Fe2+] (µM)

0.5862

75.9

0.4152

53.5

0.2646

37.7

0.1111

15.2

Plot a graph of absorbance vs concentration.

Plot of absorbance vs [Fe2+]

Slope of the plot = 0.0079 µM-1; y-intercept = -0.0174.

(b) Absorbance = 0.129. Plug in the linear equation to get

y = 0.0079x – 0.0174

===> 0.129 = (0.0079 µM-1)*[Fe2+] – 0.0174

===> [Fe2+] = 0.1464/0.0079 µM = 18.53 µM (ans).