Solution mV 1 mg/L 2043 2 mg/L 1900 4 mg/L 1800 6 mg/L 1734 10 mg/L 1663 Table 4: This table displays the measured potentials of the new standard solutions. Water Sample Measured Potential (mV) Concentrations (mg/L) Peabody 1 2273 4.640 Peabody 2 2260 4.998 Peabody 3 2267 5.085 Ohio River 1 2415 2.058 Ohio River 2 2413 2.081 Ohio River 3 2410 2.117 Miami 1 2242 5.541 Miami 2 2238 5.669 Miami 3 2237 5.702
Table 5: This table displays the measured potentials of the filtered water samples and the concentrations calculated. Water Sample Mean(mg/L) Standard Deviation Peabody 4.91 0.24 Ohio River 2.09 0.03 Miami 5.64 0.09 Table 6: This table displays the statistical analysis done with the concentrations of the water samples. DISCUSSION: The results obtained during he third period of lab support the initial hypothesis: The more rural the environment of the water sample the higher the concentration of nitrate. The water sample that was surrounded by the most pesticides and farmland was the water from the Miami and the one surrounded by an urban area was the water from the Ohio River (in downtown Cincinnati). The water sample from Peabody was an intermediate one; it is surrounded by a natural environment but in the middle of a college campus. The results found were that the water sample from Miami has the highest concentration of nitrate (5.64mg/L was the mean) at of the three water samples. Also, the water sample from the Ohio River has lowest concentration of nitrate (2.09mg/L was the mean) and Peabody has an intermediate concentration (4.91 mg/L was the mean). Although these values are in accordance with the hypothesis stated with background information, the difference between the values might not be as accurate and precise as it looks. Usually one of the reasons for error during an experiment is the cleanliness of the glass wear, but for this experiment everything was thoroughly cleaned following three steps. However, for this experiment an ISE probe was used and that could have lead to an error. For instance, the first time the potential was measured the values obtained were very high and we had to re-rinse the probe and measure again. Also, when measuring, one has to wait until it stabilizes but it never stabilizes 100% so the value recorded may change by 0.001 for example. Another aspect of this experiment that should be noted is that accuracy of the interpolation for week 2. The concentrations of the two validation samples were calculated by interpolation and the values found were (for the mean) 5.56mg/L for NA and 7.82mg/L for NB when the real values were 4.0mg/L and 8.0mg/L respectively. A t-test was performed at a 95% confidence level that showed that the value found for NA cannot be considered as equivalent to the known concentration but the value found for NB can be considered as equivalent. The RSD percentages were also calculated to see the
precision in the measurements. It was found that the percentage for NA was higher than the one for NB showing that even though, the value found for NA was more accurate than NB, the values found for NB were ore precise than the values found for NA. This shows clearly that accuracy does not imply precision and vice versa.