A fluoride electrode was used to determine the amount of fluoride in drinking water samples. The results given in the table that follows were obtained for four standards and two unknowns. Constant ionic strength and pH conditions were used.

(a) Plot a calibration curve of potential versus log [F^-]. Determine whether the electrode system shows Nernstian response.
(b) Determine the concentration of F^- in the two unknown samples by a linear least-squares procedure.

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Solution Containing F 5.00 x 10-4 M 1.00 x 10-4 M 5.00 x 10-5 M 1.00 x 10-5 M Unknown 1 Potential vs. SCE, mV 0.02 41.4 61.5 100.2 38.9 Unknown 2 55.3