A fluoride concentration was measured in a mouthwash using an ion-selective elec

Question

A fluoride concentration was measured in a mouthwash using an ion-selective electrode (ISE). The apparatus read an ISE potential of 0.8654 V, with an Econst = 0.5505V at a solution temperature of 25.0 °C. Using the Nernst equation, calculate the F- concentration in moles/L to 5 significant figures. Show your work with units. Remember that 1 Volt = 1 Joule/Coulomb

-Express the molar concentration found above (F- concentration in moles/L) as a w/v% (grams/mL) concentration of F-.Show your work with units

Explanation / Answer

Nernst equation:
E = Eo - RT/ZF log10[F-]
0.8654V = 0.5505V - (8.314*298 / 1*96485) log10 [F-]
0.3149 V = -0.02567 log10[F-]
[F-] = 5.40458*10-13 mol/L
w/v % = 5.40458*10-13 mol/ 1000 mL * (18.9984 g/mol ) = 1.02678*10-14 gm/mL

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