A student prepared the calibration curve for the analysis of fluoride via an ion

Question

A student prepared the calibration curve for the analysis of fluoride via an ion selective electrode. A 0.2055 gram sample of toothpaste was placed in a beaker, treated with total ionic strength adjusting buffer, heated and diluted to 250.0 mL. A 25.00 mL aliquate gave a reading of 245 mV. What is the % (w/w) of fluoride in the toothpaste sample?
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A student prepared the calibration curve for the analysis of fluoride via an ion selective electrode. An 0.2055 gram sample of toothpaste was placed in a beaker, treated with total ionic strength adjusting buffer, heated and diluted to 250.0 ml. A 25.00 ml aliquot gave a reading of245 mV. What is the % (w/w) of fluoride in the toothpaste sample? tive electrode. An

Explanation / Answer

From the graph it is found that log [F-] = -4.00

Thus [F-] = 10-4 (M)

Total volume of the solution is 0.25 L

So, number of moles of fluoride anion present in the solution is 10-4 * 0.25 mol = 0.000025 mol

Molar mass of fluoride anion 19 g.

So, weight of fluoride present in 0.2055 g of toothpaste is 0.000025 * 19 g = 0.000475 g

Hence, (w/w) % of fluoride in toothpaste is (000475 g / 0.2055) * 100 % = 0.23 %

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