A Ca²⁺ ion-selective electrode was calibrated with a [Ca²⁺ ] standard with a concentration of 1.00 * 10^-6. This standard gave a potential of -54 mV.

a) Construct a calibration curve.

(b) A groundwater sample from an area rich in limestone gave a potential of +16 mV. What was the [Ca²⁺] in ppm for this sample?

(c) Another groundwater sample gave a potential of -38 mV. What was the [Ca²⁺ ] in ppm for this sample?

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A Ca 2+ ion-selective electrode was calibrated in metal ion buffers with ionic strength fixed at 0.50 M. The electrode is also sensitive to Mg2+. 1a)What is the general expression for the response of this electrode, including the Mg 2+ slectivity coefficient. What is the purpose of fixing the ionic strength of the calibration points?

1b.) Derive the equation for the response of the electrode to Ca 2+ and Mg 2+ from the data below.

[Ca^2+] (M)	[Mg²⁺] (M)	mV
1.00 x 10^-6	0	-55.4
2.5 x 10^-4	0	+17.2
1.00 x 10^-6	3.7 x 10^-3	-41.1

1c.) In region rich in limestone deposits, [Ca2+] in streams is about 1.0*10-5 M. A Ca2+ ion selective electrode can be used for continuous monitoring of [Ca2+] in streams. High levels of Mg2+ can interfere with this measurement.

From answer in part (b), calculate the maximum [Mg²⁺] that can be tolerated to ensure less than a 10 % error in the measured [Ca2+].

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