The absorbance at 470 nm of the Fe(II)-phenanthroline complex was measured for several different Fe2+ concentrations in order to create a calibration curve. The absorbance at each Fe2+ concentration was measured five times. The readings, already corrected for the blank solutions, are shown below.
[Fe2+] (µM) | A1 | A2 | A3 | A4 | A5 | avg. yi | (yi-ȳ)2 | (xi-x̄)2
75.9 | 0.582 | 0.591 | 0.587 | 0.583 | 0.588 | .5862 | .0585 | 919.6
53.5 | 0.412 | 0.411 | 0.421 | 0.414 | 0.418 | .4152 | .0050 | 62.8
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
sum | 182.3 | 1.367 | 1.381 | 1.385 | 1.370 | 1.383 | 1.377 | .1242 | 1967
average | 45.575 | 0.3418 | 0.345 | 0.346 | 0.343 | 0.346 | .3443
(a) Use the averages of the replicate absorbance measurements to determine the slope and y-intercept of the best-fit straight line.
(b) Predict the Fe2+ concentration in an unknown sample that has an absorbance of 0.178.
(c) What is the uncertainty associated with the predicted Fe2+ concentration?