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QUAN6DATARESULTS.docx
Data & Results
Table 1: Determination of Fluoride by Ion Se lective Electrode: Measurements
|
(ppm) |
log (F-) |
(mV) |
|
0.5 |
-0.3010209 |
-22.0 |
|
1.0 |
0 |
-23.1 |
|
2.0 |
0.30103 |
-19.4 |
|
5.0 |
0.69897 |
-14.2 |
|
10.0 |
1 |
-6.0 |
|
20.0 |
1.30103 |
-1.3 |
|
Mouthwash |
|
-5.0 |
Figure 1: mV vs. Log [F-]
Calculations:
0.5 ppm = 0.5 ug/ml
1 mol of Fluorine = 19.00g
0.5 ug/ml x 1g/ 106 x 1000 ml/L x 1mol/19.00g = 2.6316 x 10-5 M
1.0 ug/ml x 1g/ 106 x 1000 ml/L x 1mol/19.00g = 5.2632 x 10-5 M
2.0 ug/ml x 1g/ 106 x 1000 ml/L x 1mol/19.00g = 1.0526 x 10-4 M
5.0 ug/ml x 1g/ 106 x 1000 ml/L x 1mol/19.00g = 2.6316 x 10-4 M
10.0 ug/ml x 1g/ 106 x 1000 ml/L x 1mol/19.00g = 5.2632 x 10-4 M
20.0 ug/ml x 1g/ 106 x 1000 ml/L x 1mol/19.00g = 1.05 x 10-3 M
Linear Equation of Regression
y = 14.049x – 21.358
x= (y + 21.358)/ 14.049 then take antilog
x= (-5 + 21.358)/ 14.049 = 1.164
101.164 = 1.459 x 10 M
F- in Mouthwash = 1.459 x 101 mol/L x 19g/mol x 1000mg/ 1g = 2.772 x 105 ppm
Table 2: Measured Voltage and Calculated Molarity
|
Volume (ppm) |
Molarity |
mV |
Log of Molarity |
|
0.5 |
2.6316 x 10-5 M
|
-22.0 |
-4.580 |
|
1.0 |
5.2632 x 10-5 M |
-23.1 |
-4.279 |
|
2.0 |
1.0526 x 10-4 M |
-19.4 |
-3.978 |
|
5.0 |
2.6316 x 10-4 M |
-14.2 |
-3.580 |
|
10.0 |
5.2632 x 10-4 M |
-6.0 |
-3.279 |
|
20.0 |
1.05 x 10-3 M |
-1.3 |
-2.970 |
Figure 2 : Molarity vs mV readings
y= 21658x – 21.638
Discussion
While distributing the F- ion calibration standards into each respective volumetric flask, it was important to note that this solution could not stay in glassware for long periods of time due to its toxic corrosive nature. The usage of a Fluoride ISE requires paying close attention to many details. Some general precautions consisted of; 1) not damaging the sensitive electrode tip, 2) holding on to the FISE while conducting measurements, 3) not letting the electrode time touch the bottom of the beaker and 4) avoiding contact with organic solvents and strong bases. When reading the Fluoride ISE results, the lab results may have been thrown off due failure to clean the electrode between each reading of the different calibration solutions. After completing the potentiometric measurements of the different standard solutions , the calibration curves for “mV readings vs lo of concentration” and “Molarity vs mV readings” were plotted for slope analysis. The slope equation [y = -49.104x - 372.61] from the first graph was used to plug in the mouthwash values (y=-447,x=1.515) to find the antilog yielding the mouthwashes’ molarity. The “Molarity vs mV readings” graph produced the calibration curve that allowed “m”, the slope in the equation “y=mx+b” to be solved. The m value was then compared to Nernst Equation prediction of m being having a slope value of 59.16 under ideal conditions. The slope for the second graph was (m) -71688. This value was significantly lower then the Nernst Equation prediction meaning that the membrane is not in thermodynamic equilibrium. When the graph was plotted with the mouthwash values at 25 ppm , 3.273 M & -447mV, the equation was y=1.5226x - 397.17 with a slope of m=1.5226 being closer to the Nenrst Equation, but the graph was unreadable.
Calibration Curve
-0.30102089999999998 0 0.30103000000000002 0.69896999999999998 1 1.3010299999999999 -22 -23.1 -19.399999999999999 -14.2 -6 -1.3
Log (F-)
mV Readings
Molarity 2.6316E-5 5.2632E-5 1.0526000000000001E-4 2.6316000000000002E-4 5.2632000000000004E-4 1.0499999999999999E-3 -22 -23.1 -19.399999999999999 -14.2 -6 -1.3
Molarity
mV
