Potentiometry is an electroanalytical technique that measures the potential voltage between two electrodes in a solution to determine the concentration of a specific ion. In this case, we want to determine the concentration of chloride ions Cl- in a water sample collected from a lake. To do this, we can use an ion-selective electrode ISE that is sensitive to chloride ions, such as a silver/silver chloride Ag/AgCl electrode, and a reference electrode, typically a saturated calomel electrode SCE or a silver/silver chloride Ag/AgCl reference electrode.Here is a step-by-step procedure to determine the concentration of chloride ions using potentiometry:1. Calibration: Prepare a series of standard solutions with known concentrations of chloride ions e.g., 1, 10, 100, and 1000 mg/L . Measure the potential voltage between the chloride ISE and the reference electrode for each standard solution. Plot the measured potentials against the logarithm of the chloride concentrations to create a calibration curve.2. Sample preparation: Collect a water sample from the lake and filter it to remove any suspended particles that may interfere with the measurement. If the sample has a very low or high pH, adjust it to a neutral range around pH 7 using appropriate buffer solutions.3. Measurement: Immerse the chloride ISE and the reference electrode in the water sample. Allow the potential to stabilize, and then record the measured potential.4. Calculation: Use the calibration curve obtained in step 1 to determine the concentration of chloride ions in the water sample. Locate the measured potential on the y-axis of the calibration curve, and then find the corresponding chloride concentration on the x-axis by taking the antilogarithm of the value.5. Quality control: To ensure the accuracy of the measurement, analyze a quality control sample with a known concentration of chloride ions alongside the water sample. The measured concentration should be within an acceptable range of the known concentration.By following these steps, potentiometry can be effectively used to determine the concentration of chloride ions in a water sample collected from a lake.