A calibration experiment for a cobalt complex yielded the following linear-regression…

CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures

Problem

A calibration experiment for a cobalt complex yielded the following linear-regression parameters (95 % confidence limits): slope

m = 1.428 \pm 0.028\;\text{(dimensionless per mM)}

intercept

b = 0.003 \pm 0.005

The absorbance of an unknown solution was measured three times, giving a mean value of

A_{\text{unknown}} = 0.533

with a standard deviation of

0.006

. All measurements were performed in the same 1.00 cm cuvette. (a) Calculate the concentration of Co(II) in the unknown solution using the regression equation obtained from the standards. (b) Propagate the uncertainties in

m

b

, and

A_{\text{unknown}}

to determine the absolute uncertainty (at the 95 % confidence level) in the calculated concentration. State any assumptions used in the propagation. (c) Report the concentration of Co(II) in the unknown solution with its combined uncertainty and the correct number of significant figures.

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