Determining Fluoride in Tap Water Using the Fluoride Ion Selective Electrode

Determining Fluoride in Tap water using the Fluoride Ion Selective Electrode

Background Reading: Skoog, West, Holler and Crouch, 7th ed., Chap. 19. Harris, 5th ed., Chap. 15. Harris, 7th ed., Chap. 15.

Pre-Lab

1. Fluoride ion selective electrodes obey the following equation. Determine K for such an electrode if a 10.5 mg/L of NaF gave a response of -0.375 V?

E (V) = K – 0.059*log[F-]

2. Calculate [F-] if a solution was dipped into the same electrode in Question 1 and gave a response of -0.425 V.

3. A potential of 100.2 mV is measured for a fluoride ion selective electrode in a solution of 1.00 x 10-5 M fluoride at pH 5.00. Calculate the potential that would be measured if the solution pH were 10.00, assuming the selectivity coefficient for OH- is 0.1.

4. Calculate the pH of a buffer solution that is 75% acetic acid and 25% sodium acetate.

5. Fifteen mL of a sample solution was diluted to 50 mL in a volumetric flask. The F- concentration of this DILUTED sample was determined with a F ion selective electrode and found to be 5.5 mg/L. What is the concentration of F- in the original, undiluted sample?