Assignment:
The data below is obtained with a potassium ISE. To avoid interferences from H+ and variations in ionic strength all solutions were made to contain 0.33 M Ca(NO3)2 and 0.0010 M NaOH. An unknown solution was similarly prepared and gave a reading of -0.0273 volts.
a) What is the slope of the ISE response? (This is the same as the coefficient of the log term in the ISE equation). What is the value of E', (also known as k)?
b) What is the concentration of K+ in the unknown?
c) What is the lowest [K+] value that can be accurately measured using the ISE and the procedure described?
d) What is selectivity constant, kK,Na , for the ISE?
|
Log [K+]
|
E (volts)
|
|
-1.3
|
-0.165
|
|
-2.3
|
-0.221
|
|
-3.0
|
-0.259
|
|
-3.7
|
-0.298
|
|
-4.7
|
-0.350
|
|
-5.3
|
-0.381
|
|
-6.3
|
-0.413
|
|
-7.0
|
-0.421
|
|
-8.0
|
-0.424
|
|
-9.0
|
-0.424
|