The blank solution used to calibrate the spectrophotometer is 10.0mL of 0.2M Fe(NO3)3 diluted to 25.0mL with 0.1M HNO3. Why is this solution preferred to simply using de-ionized water for the calibration?

This solution is preferred to using de-ionized water for the calibration because it provides a more accurate and reliable calibration. The Fe(NO3)3 solution provides a known concentration of a colored compound, which can be used to accurately measure the absorbance of the spectrophotometer. De-ionized water does not provide a known concentration of a colored compound, so it is not as reliable for calibrating the spectrophotometer.

The blank solution used to calibrate the spectrophotometer is preferred to using de-ionized water alone for calibration due to a few reasons.

Firstly, using de-ionized water does not take into account any potential interferences or background absorbance that may occur in the sample being measured. The blank solution, on the other hand, mimics the sample matrix by including similar reagents and diluents. In this case, the blank solution consists of 0.2M Fe(NO3)3 diluted in 0.1M HNO3. By using a solution that closely resembles the sample, any interferences or background absorbance caused by the matrix can be accounted for and subtracted from the measurements of the actual sample.

Secondly, the blank solution helps to correct for any inherent absorbance of the spectrophotometer itself. Every instrument has a certain level of background absorbance which needs to be taken into account for accurate measurements. By using a blank solution with known concentration and composition, any absorbance caused by the instrument can be measured and subtracted.

By calibrating with the blank solution, the spectrophotometer can be accurately calibrated to account for any interferences or background absorbance, and provide more reliable and accurate measurements of the actual sample.

The blank solution used to calibrate the spectrophotometer contains 10.0 mL of 0.2 M Fe(NO3)3 diluted to 25.0 mL with 0.1 M HNO3. This solution is preferred over using deionized water for calibration due to a few reasons:

1. Eliminating systematic errors: Deionized water alone does not account for any systematic errors that may exist in the sample measurement process. By using a blank solution containing known concentrations of Fe(NO3)3 and HNO3, it helps to correct for any potential systematic errors that may affect the accuracy of the spectrophotometer.

2. Accounting for baseline absorbance: When using deionized water as a blank, it assumes that the absorbance readings of the sample will be zero, which is not always the case. Some substances or impurities in the sample may contribute to a non-zero baseline absorbance. Therefore, using a blank solution with known concentrations of Fe(NO3)3 and HNO3 allows for better baseline correction, leading to more accurate measurements.

3. Considering instrument drift: Spectrophotometers may experience changes in baseline absorbance over time due to instrument drift. By using a blank solution with known analyte concentrations, it helps to account for any changes in instrument drift, resulting in more reliable and consistent measurements.

Overall, using a blank solution with known concentrations of Fe(NO3)3 and HNO3 instead of deionized water improves the accuracy and reliability of spectrophotometer calibration by accounting for systematic errors, baseline absorbance, and instrument drift.