Ise Determination of Fluoride Content in Various Substances

Category: Chemistry
Last Updated: 12 Mar 2023
Pages: 2 Views: 111

Introduction: The ion-selective electrode used was made up of a silver/silver chloride reference electrode and a glass electrode. The pH of the electrochemical cell is determined by monitoring the electrical potential difference between the half-cells. The glass electrode is an ion-selective electrode (ISE), which only responds to the hydronium ion concentration/activity in a solution under a large range of conditions.

In this experiment, we are measuring the fluoride ion concentration, which means our electrode responds to fluoride ion concentrations.

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Standard Solutions Concentration (M) Potential (mV)
0. 9967 x 10-6 15. 0
0. 9967 x 10-5 1. 4
0. 9967 x 10-4 -42.
0. 9967 x 10-3 -101. 1
0. 9967 x 10-2 -160. 8
0. 9967 x 10-1 -219. 0

Unknown #6 was used for this lab group. It produced a potential difference of -196. 8 mV. This was then used in the equation derived from our standard solutions and found to have a [F-] = 0. 0618 M. Preparation of the toothpaste sample was done by a sonicator. Then, the electrical potential difference was measured again, just as in the standard solutions and unknowns. It was found to have a potential of -85. 6 mV.

Inserted into the equation, [F-] = 3. 31 x 10-4 M.

Calculations: See attached sheets.

Results: Toothpaste [F-] = 3. 31 x 10-4 M

Unknown #6 [F-] = 0. 0618 M Label Value in Toothpaste 0. 15% w/v Calculated Value in Toothpaste 0. 8 mg / g 0. 8 mg/g converted to w/v (g/100 mL) is approximately 0. 1144% w/v. In comparison with the label, the calculated error is found to be about -24%. A potential source of error could be found in the method of dissolving the toothpaste. There were a lot of bubbles formed, thus allowing for a greater possibility of misreported volumes of solution. Also, the pH / V meter had difficulty settling on values during the standard measurements, which would alter the regression line. The ISAB seemed to work better with stronger concentrations of [F-], as the regression line fit better toward the latter part of the plot. However, the pH region seemed to be less important than the [F-] concentration.

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Ise Determination of Fluoride Content in Various Substances. (2018, Feb 05). Retrieved from

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