Question

Fluoride ion selective electrodes obey the following equation: E(V) = K - B(0.0592)log[F] where the fluoride concentration is expressed as mol/L and the temperature coefficient B is normally equal to 1. In a normal calibration procedure you dilute a standard fluoride solution to between 10 and 20 mg/L fluoride ion and then measure the response of the electrode. You then plot the data and do a linear regression to obtain the fitting coefficients K and B. Use the plotting and linear regression tools in Excel to calculate K and B from the data in the table. The coefficient B is close to 1, and can be determined from a calibration curve. F concentration (mg/L) E(V) 10.0 -0.306 -0.310 12.0 14.0 -0.314 16.0 18.0 -0.317 -0.320 -0.323 20.0 What value of K do you obtain from your plot? What value of B do you obtain from your plot?

Answer 1

[F-]	log[F-]	E
10	1	-0.306
12	1.079181	-0.31
14	1.146128	-0.314
16	1.20412	-0.317
18	1.255273	-0.32
20	1.30103	-0.323

E vs log[F-] 0.304 12 0.2 0.4 0.6 0.8 1.4 -0.306 0.308 0.31 -0.312 E-0.314 0.316 0.318 y-0.0562x-0.2495 -0.32 -0.322 -0.324 log[F-

from equation of curve in comparison with formula

K = intercept of curve = -0.2495

slope = -$\beta$ (0.0592) = -0.0562

so, $\beta$ = 0.949