ISE Ion selective electrode determination of fluoride Section Give brief answers

Question

ISE Ion selective electrode determination of fluoride Section Give brief answers descriptions for the following questions. Use the back or additional pages if required. Tum this worksheet in before you leave lab on the day that you perform the 1. What is the scientific rationale for including fluoride in domestic drinking water supplies and in dental care products? 2. What is the targeted concentration range for fluoride ion in domestic drinking water supplies? 3. Calculate the amount of NaF required to prepare 1 liter of a solution containing 100 ppm F. 4. Describe a practical strategy for performing the dilutions necessary to cover the range of fluoride concentrations needed to construct the calibration curve in this experiment.

Explanation / Answer

1. The purpose of addition of fluoride to drinking water is to prevent tooth decay there by preventing cavities.

2. The acceptable range of fluoride in drinking water is from 1 ppm to 1 mg/L

3. 1 ppm = 1 mg/L, 100ppm = 100 mg/L

1 L contains 100 mg of F-. Molar mass of NaF= 23+19=42, mass % of F in NaF= 100*19/42= 45.25%

Hence quantitiy of NaF= 100/0.4525= 220.9945 mg

4. The purpose of calibrations at different concentrations enables one to develop a calibration chart of concentration of fluodie and voltage. From the voltage of unknown solutions, concentration can be calculated.

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