3. What experimental problems would confront you if you attempted to determine the concentration of the metal ions in solutions of each of the following reagents?
a. Cr +3 which has a maximum absorbance at 407 nm with absorbtivity of 15 M -1 cm -1 and another at 574 nm with absorbtivity of 13 M-1 cm -1
b. Mn 2+ which has a maximum absorbance at 530 nm with absorbtivity of .050 M - 1 cm -1.
c. Zn+3 which does not absorb light between 400 and 600 nm
To determine the concentration of metal ions in solutions, typically a technique called absorption spectroscopy is used. Absorption spectroscopy measures how much light is absorbed by a sample at different wavelengths. The concentration of the metal ions can then be determined by comparing the measured absorbance to a calibration curve.
a. For Cr+3, the experimental problem you would encounter is that it has two absorption peaks at different wavelengths. This means that you would need to measure the absorbance at both 407 nm and 574 nm to accurately determine the concentration. You would need a spectrophotometer that allows you to record absorbance at multiple wavelengths. Additionally, you would need to measure the absorbance of known standards with known concentrations of Cr+3 at these two wavelengths to create a calibration curve.
b. For Mn2+, the experimental problem you would face is relatively straightforward compared to Cr+3. The absorbance of Mn2+ has a maximum at 530 nm, and you would need to measure the absorbance of the solution at this wavelength. The main issue you might face is the low absorptivity value of 0.050 M-1 cm-1, which means that the absorbance might be quite low. Ensure that you use a spectrophotometer with high sensitivity or consider using a higher concentration of Mn2+ to increase the absorbance.
c. Zn+3, according to the information provided, does not absorb light between 400 and 600 nm. This could be viewed as a challenge because it means that you would not be able to use absorption spectroscopy at these wavelengths to directly determine the concentration of Zn+3. You would need to use an alternative analytical technique, such as atomic absorption spectroscopy or inductively coupled plasma-mass spectrometry, which can specifically detect and quantify metal ions in a sample. These techniques rely on different principles than absorption spectroscopy and would require specialized equipment.
In summary, when attempting to determine the concentration of metal ions in different reagents, you need to consider the specific wavelengths at which they absorb light and the absorptivity values. Multiple peaks, low absorbance values, or the absence of absorption within a desired wavelength range might present experimental challenges that require adjustments to the experimental setup or the adoption of different analytical techniques.