What is the color of the complex formed from the reaction of Co2+ and quercetin? Does the complex formed follow the Beer-Lambert's Law? What is the regression equation derived from the analysis of calibration standard solutions? What is the absorptivity coefficient of the complex formed? What is the concentration of Co2+ (in ppm CoCO3) in the stream water? (AW (g/mol): Co = 58.93, C = 12.01, O = 16.00)
Janine's research focuses on the ability of quercetin, a flavonoid and natural dye, to detect the presence of Co2+ in wastewater samples. She prepared a set of calibration standard solutions by adding an excess of quercetin to solutions of varying Co2+ concentration and maintaining it at pH 6.4 using a Tris-HCl buffer. The reaction yields a colored complex solution that has a maximum absorbance at 440 nm:
Co2+ + 2 Quercetin --> Co(Quercetin)22+
The absorbance measurements for the calibration solutions prepared are shown in the tables; a cuvette with a 2.50 cm path length was used.
| [Co2+], in M | Absorbance | Color | Wavelength range (nm) |
| 0.05 | 0.100 | Red | 625-740 |
| 0.10 | 0.166 | Orange | 590-625 |
| 0.20 | 0.285 | Yellow | 565-590 |
| 0.30 | 0.367 | Green | 490-565 |
| 0.40 | 0.454 | Blue | 440-490 |
| 0.50 | 0.571 | Violet | 380-440 |
Part of her research is to determine the extent of Co2+ pollution in a stream near a pharmaceutical company. She obtained a 50.0-mL sample of the stream water and buffered it to pH 6.4. She then added excess quercetin to a 5.00 mL aliquot of the buffered sample solution, transferred it to a 25.0-mL volumetric flask, and diluted it to mark with distilled deionized water. She transferred a 1.00-mL aliquot of the resulting solution into a cuvette and obtained an absorbance measurement of 0.123 AU.
- What is the color of the complex formed from the reaction of Co2+ and quercetin? Does the complex formed follow the Beer-Lambert's Law?
- What is the regression equation derived from the analysis of calibration standard solutions?
- What is the absorptivity coefficient of the complex formed?
- What is the concentration of Co2+ (in ppm CoCO3) in the stream water? (AW (g/mol): Co = 58.93, C = 12.01, O = 16.00)
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