Question

The absorbance at 470 nm of the Fe(II)-phenanthroline complex was measured for several different Fe 2 + concentrations to create a calibration curve. The absorbance at each Fe 2 + concentration was measured five times. The absorbance values, already corrected for the blank absorbance, are shown in the table.

[Fe2+Fe2+] (μM)	A1A1	A2A2	A3A3	A4A4	A5A5	average yiyi	(yi−¯y)2(yi−y¯)2	(xi−¯x)2(xi−x¯)2
	75.9	0.582	0.591	0.587	0.583	0.588	0.5862	0.0585	919.6
	53.5	0.412	0.411	0.421	0.414	0.418	0.4152	0.0050	62.8
	37.7	0.264	0.266	0.269	0.258	0.266	0.2646	0.0063	62.0
	15.2	0.109	0.113	0.108	0.115	0.111	0.1112	0.0543	922.6
sum:	182.3	1.367	1.381	1.385	1.370	1.383	1.377	0.1242	1967
average:	45.575	0.3418	0.345	0.346	0.343	0.346	0.3443

Use the averages of the replicate absorbance measurements to determine the slope and y -intercept of the best-fit straight line. m = 0.008 μ M − 1 b = −0.0176 Determine the Fe 2 + concentration in an unknown sample that has an absorbance of 0.170 .

Answer 1