Example Of Methodology Report
A Two-Part Experiment: Spectrometric Method for the Determination of Olive Oil Grade Using Spectra Matching and Determination of Nickel (II) Nitrate Concentration Using Beer’s Law
Beers’s law is an important concept in chemistry. According to this concept, the concentration of a compound is directly proportional to its degree of absorbance. This means that as the concentration of a colored compound increases then its absorbance will also increase. This concept is usually employed in the determination of the concentration for a particular compound. In accordance with the concept of Beer’s law, chemists usually employ spectrum matching to determine the identity of unknown compounds. Accordingly, the height of the peaks of absorbance can be used to determine the grade or the identity of unknown compounds.
These two concepts were used in this two-part experiment. The first part involved the determination of the identity of the grade of an unknown sample of olive oil by using spectrum matching. The second part involved the concentration determination of nickel (II) Nitrate through the use of Beer’s Law.
Both parts (part I and part II) made use of the spectroscopic method. This method involves the observation and quantification of the interaction of unknown samples with light. In this particular laboratory experiment, the measure parameter is absorbance. Absorbance pertains to the amount of light that the unknown absorbs a light is bombarded to it.
For the first part, three standard solutions of Olive oils were first prepared. These olive oils have different grades: Extra Virgin, Regular, and Light Olive oil. The absorbance spectrum of each of these standards were then determined. Lastly, a sample of olive oil with unknown grade was prepared. The spectrum of this unknown was also determined and was compared to the spectra of each of the three standards. Whichever spectra match the unknown was concluded to be the grade of the unknown olive oil.
For the second part, standard Nickel nitrate solutions with known concentrations were made. The absorbance of each of these standards was obtained at 659nm. A standard curve was then generated based on the concentrations and their corresponding absorbance. The best fit curve was determined using the Microsoft Excel application. The equation of the best fit curve was also determined. The unknown sample was then subjected to the same procedure as the standard to obtain its level of absorbance. The absorbance reading value was then substituted to the dependent variable (Y) of the equation to determine its corresponding concentration.
For the first part of the experiment, all the spectrum of each of the standards has two unique peaks. The spectra of the unknown sample are similar to the spectra of the light grade olive oil.
For the second part of the experiment, the best fit curve is a straight line that rises to the right of the first quadrant as shown in figure 1. The equation of the best fit curve is y = 1.575x + 0.020, where y is the absrobance and the x is the concentration. The data for making figure 1 is given in table 1.
Figure 1: The standard curve the determination of Nickel Nitrate concentration
The absorbance of the Unknown A is 0.195. When this value is subtitude to the equation its corresponding concentration can be known. Accordingly:
x = (y – 0.020)/1.575
x = (0.195 – 0.020)/1.575
x = 0.111ppm
The three standard olive oil solutions have their respective colors, accordingly: Extra virgin – greenish, Regular – yellowish, and Light - clear. This differences in their resppective colors would result to the different height in their absorbances on the two ranges: 400 to 500 nm and 600 to 700 nm. The peaks of the extra virgin olive oil will be most pronounced while the peaks of the light olive oil will be the least pronounced. The peaks on tehs pectra of the unknown matches thoseof the light olive oil. Note that by mixing the extra virgin and light olive oils, the spectra that it produced is similar to the regular olive oil. This is because the green and yellow pigmentations in the extra virgin olive oil were dilluted by the light olive oil.
On the Nickle Nitrate solutions, it should be noted that an expert in analytical chemistry could make an estimate of its concentration even without the aid of a spectrometer. Note that the Nickle Nitrate solution is colored. The intensity of the color is directly proportional to the concentration of the nickle nitrate in it. Hence, an intense-colored solution would have high nickle nitrate concentration while a lightly-colored solution would ony have very low nickle nirate concentration. Nevertheless, using a spectrometer would give more accurate results. For this experiment, the concentration thatw as determined is 0.111ppm. It should be noted that the Beer’s law is alsoapplicable to Cobalt (II) Nitrate solutions which are colored red. When a solution has a color, then it means that it absorbs light; hence, its absorbance can be determined. As a rule, Beer’s Law can be applied to all colored compounds.
This experiment concludes that the Beer’s law and spectra matching are effective ways to determine the grade and concentartion of olive oil and nickle nitrate, respectively. It also concludes that such techniques are only applicable to colored solutions.
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