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.
To determine the concentration of metal ions in the solutions of the given reagents, you would typically use a technique called spectrophotometry. This method relies on the measurement of the absorption of light by the metal ions in the solution.
Let's address each reagent and the potential experimental problems you may encounter when trying to determine the concentration of metal ions:
a. Cr +3 with maximum absorbance at 407 nm and 574 nm:
- Dilution: One of the potential problems is the concentration of the solution. If the concentration of the metal ion is too high, it might exceed the upper limit of the spectrophotometer's detection range. In such cases, you would need to dilute the solution and determine the new concentration.
- Interference: The presence of other substances in the solution could interfere with the absorption measurements at the specific wavelengths. This could lead to inaccurate results. You would need to ensure that there are no interfering substances in the solution or find a way to remove them.
- Overlapping Absorption Peaks: In this case, the reagent has two absorption peaks at different wavelengths. If these peaks overlap significantly, it can lead to difficulty in accurately measuring the absorbance at each peak. In such situations, you might need to consider using a different wavelength or employing mathematical techniques to deconvolute the overlapping peaks.
b. Mn 2+ with maximum absorbance at 530 nm:
- Sensitivity: The given absorptivity (molar absorptivity) value is quite low, which means that the absorption of light by the Mn 2+ ions might be weak. This can result in low absorbance readings, which could make it challenging to accurately determine the concentration. You might need to use a more sensitive method or consider increasing the path length (cm) to increase the absorbance value.
- Calibration: To determine the concentration accurately, it is crucial to have a calibration curve. You will need to prepare a series of standard solutions with known concentrations of Mn 2+ ions and measure their absorbance at 530 nm. This will allow you to establish a linear relationship between concentration and absorbance. The resulting calibration curve can then be used to determine the concentration of Mn 2+ ions in the unknown solutions.
It's important to note that these are some potential problems you might encounter, but other factors like sample preparation, stability of the solution, and instrument calibration should also be considered during the experimental procedure.