Calibration data for a F-ion-selective electrode using KF standard solutions prepared in buffer of 0.5 M ionic strength is given in the table below. This fluoride ion-selective electrode has selectivity coefficient of 0.001 for chloride ions. Construct calibration curve, perform least-squares linear regression as appropriate and determine the magnitude of β for this particular electrode.
|
[KF] (M)
|
E (mV)
|
|
1.00
|
0.0
|
|
1.0×10-1
|
52.2
|
|
1.0×10-2
|
106.1
|
|
1.0×10-3
|
161.7
|
|
1.0×10-4
|
217.4
|
|
1.0×10-5
|
276.1
|
|
1.0×10-6
|
323.0
|
|
1.0×10-7
|
340.0
|
|
1.0×10-8
|
345.0
|
(b) An unknown sample of tap water as analyzed 5 hours after the above calibration data was collected. E measured was 341.0 mV. what is he concentration of F-in this tap water sample? How accurate is this concentration and explain your reasoning?
(c) An unknown sample of ocean water was analyzed immediately after the above alibration data was collected. E measured was 142.0 mV. What is the concentration of F-in this ocean water sample? How accurate is this concentration and explain your reasoning?
(d) What (if anything) would you do differently if you were performing the analyses described in (b) and (c) to increase the accuracy of the [F-] determination? For full marks, be very clear and specific.