Answer question 2 asap please EXPERIMENT 9: ION-SELECTIVE ELECTRODES The determi

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Answer question 2 asap please

EXPERIMENT 9: ION-SELECTIVE ELECTRODES The determination of the concentration of both cations and anions in solu tions can take several forms, including spectrophotometry, complexation titrations, precipitation titrations, etc. For several potential analytes (like Na, K, Ca, Cl, NO,, F), the ion-selective electrode (ISE) represents one of the most attractive and straightforward means of determining solu tion concentrations. An ideal quantitative technique would involve placing a "probe" in the sample to be measured and then "reading out" the concentrations of all chemical species present. Potentiometric techniques approach this ideal situation. The probe (the ISE) is placed into a sample solution and is con nected to a potentiometer, a device for measuring the potential (voltage) differences between the ISE and a reference electrode. If the conditions of the measurement are well understood and controlled, the potential differ- ence between these two electrodes can be related to the concentration of a specific chemical species present in the sample. OBJECTIVES Educational Objectives A student who has successfully completed this experiment will be able to: . prepare a series of standards using a serial dilution, make voltage measurements using an ISE generate a calibration plot using voltage measurements, and determine the molarity of an ion from ISE measurements

Explanation / Answer

Potentiometric measurements depend on the conductivity of solution being measured.

For reliable measurements the conductivity of all solutions being measured should be same.This is achieved by ionic strength adjustor. We do it because,  by bringing the ionic strength of all samples and standards to a similar level, the effect of variable ionic strengths on the activity (and therefore the concentration) is minimized, thus reducing measurement error.

Solution suitable as ionic strength adjustor will be different for different electrode.

examples

for Sodium ion 1M NH4Cl

for Calcium ion 2M KCl

for Chloride ion 5M NaNO3

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