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The great group project 2024

By: Nhi and Trent Group: I don't know

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Table of contents.

1- Purpose 2-Results 3- Calculations 4- Discussion 5- Conclusion

1) Purpose

The purpose of this experiment was to determine the concentration of an unknown solution using standard solutions of Chromium nitrate and analyze them with a spectrometer. Once the necessary absorbance data had been collected, a calibration curve was created to determine the concentration of the unknown. The experiment was also conducted to compare the data found to the findings of other groups.

The spectronic used : #6

Table 1: Absorbances measured of Chromic Nitrate

Results

Table 2: Absorbances measured of Chromic Nitrate of Group Data

Results

Figure 1: The relationship between the measured absorbance and the concentration of chromic nitrate.

Results

Figure 2: The relationship between measured absorbance and the concentration of chromic nitrate. (without the blank)

Results

Figure 3: The relationship between measured absorbance and the concentration of chromic nitrate with the unknow data.

Results

Figure 4: The relationship between measured absorbance and the concentration of chromic nitrate of Group Data.

Results

Finding the concentration of the unknown solution :

• After plotting the data in Excel, the calibration curve equation was received.
• y = 3.11x + 0.0003
• (it is worth noting that we used the equation of the graph without the blank, ensuring our value was as accurate as possible).
• The average absorbance value of the unknown measured is 0.172
• Using the equation of the line, the unknown was found to have a concentration of 0.055 mol/L
• ((0.172 - 0.0003) / 3.11) = 0.055 mol/L

Calculations

In terms of Group Data:

• After plotting the data in Excel, the calibration curve equation was received.
• y = 2.8256x + 0.0033

• The average absorbance value of the unknown measured for Group Data is 0.154
• ((0.154 +0.0033) / 2.8256) = 0.056 mol/L
• Using the equation of the line, the unknown was found to have a concentration of 0.056 mol/L
• The percentage difference of the group I don't know compared to the Group Data is 1.80%

Calculations

Overall, the experiment was a success. Standard solutions of chromium nitrate were created and analyzed in a spectrometer. Triplicates of each standard and the unknown were measured to capture the necessary data. All data that was collected in the lab can be found on slide 4. Using the equation of the line and the average absorbance score of the unknown, the concentration of the unknown was determined to be 0.055M. This value raises some questions because the unknown that was used was created by another group and was meant to have a concentration of 0.05 mol/L. This may result from the solution not being thoroughly mixed before use or the standard solution (unknown) not being appropriately created (too many moles of chromium nitrate in the 1 L solution). The concentration value may have also been affected by the calibration of the spectrometer.

Discussion

As the concentration of samples increases, the absorbance increases accordingly. Each concentration did show minor fluctuations in values but overall the data is comparable.

Using the data collected by each group (with the exception of two) an Excel chart was constructed to compare and contrast the data. Two groups were excluded from the final chart because their unknown and or standard solutions did not share similar values found by the other groups. Each of the selected groups had similar findings, showing a positive relationship between concentration and absorbance.

Discussion

• This may be the result of the solution not being thoroughly mixed before use, or the standard solution (unknown) was not created properly (too many moles of chromium nitrate in the 1 L solution).
• Practically, there are other sources of error, such as environmental effects on the photometer, sample, and temperature.
• Although the maximum wavelength used was the same, at 510 nm, each group analyses their sample with different spectrometers, each spectrometer could be calibrated differently from each machine.
• There could be systematic errors when choosing the unknown to analyze.

Sources of error.

Discussion

In conclusion, the great group project was a success. After creating and analyzing standard solutions of chromium nitrate, an unknown was analyzed to determine the absorbance and concentration. The unknown was found to have an average absorbance of 0.172 and a concentration of 0.055mol/L. This concentration value raises some questions because the expected value for the unknown was estimated to be around 0.05 mol/L. It is likely that the unknown solution was not properly created or mixed before use. The data found was compared to the findings of other groups. Each group (used) had similar findings, showing positive correlations between the concentration of solution and absorbance. The data was combined and a calibration curve was created to represent all of the data. Using the group data and equation of the group calibration curve, the average concentration of the unknown was determined to be 0.056mol/L.

Conclusions

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