CHM 222 – A
4 / 20 / 2007
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. Procedure
|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 | |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...