The following data were obtained when a Ca²⁺ ion-selective electrode was immersed in standard solutions whose ionic strength was constant at 2.0 M.

(a) Prepare a calibration curve and find the least-squares slope and intercept and their standard deviations.

(b) Calculate the value of in Equation 14-13.

(c) For a measured potential, the calibration curve gives us log[Ca²⁺]. We can compute [Ca²⁺] = 10^log[Ca2+] . Using rules for propagation of uncertainty in Table 3-1, calculate [Ca2+] and its associated uncertainty of a sample that gave a reading of -22.5 (± 0.3) mV in four replicate measurements.

Equation 14-13

Ca+ (M) E (mV) 3.38 x 10 -74.8 3.38 X 10 -46.4 3.38 X 10 3.38 X 10-2 3.38 X 10 -18.7 +10.0 +37.7