Why is a blank solution used in absorption spectroscopy? I know it is to nullify the reflection, refraction, and diffraction that occurs, but if the blank solution was a dilute solution rather deionized water, how would the concentration of Cr(VI)in a sample be affected?
When a blank is used the spectrophotometer is made to read 100% with the blank inserted (you may make it read A = 0 which is the same as 100%T). So if you set the unit to read 100%T (0 Absorbance) with the blank, what will it read if you next insert a dilute Cr solution. We don't know exactly what it will read but we know it will read less %T (more absorbance) because the dilute Cr solution absorbs some of the light. Now suppose you make that dilute Cr solution read zero with the adjustment knob. Then you measure an unknown with that setting. Suppose the unknown SHOULD HAVE READ 50
%T but it won't read that now. It will read something like 60%T (less absorbance). Less absorbance means less Cr so the results will be low. Check my thinking.
Using a blank solution in absorption spectroscopy is important to measure the absorption of the analyte accurately by nullifying the effects of reflection, refraction, and diffraction. While deionized water is commonly used as a blank solution, other dilute solutions can also be used depending on the nature of the analysis.
If a dilute solution is used as a blank instead of deionized water, it is crucial to ensure that the concentration of the analyte (in this case, Cr(VI)) in the blank solution is negligible or significantly lower than the concentration in the sample. Otherwise, the presence of the analyte in the blank solution will introduce an additional absorbance value that can lead to inaccurate calculations.
To avoid the interference caused by the blank solution, it is important to select a suitable blank with a low or negligible concentration of the analyte. This ensures that the absorption readings obtained from the sample are only due to the presence of the analyte in the sample and not influenced by the blank solution.
In absorption spectroscopy, a blank solution is used as a reference to account for the effects of reflection, refraction, and diffraction that occur when light passes through the sample. By measuring the absorbance of the blank solution, these undesired effects can be subtracted from the absorbance of the sample, resulting in more accurate measurements.
Now, regarding your question about the impact of using a dilute solution instead of deionized water as a blank solution on the concentration of Cr(VI) in a sample, let's break it down step by step:
1. First, it's important to note that the blank solution used should ideally be chemically similar to the sample being analyzed. So, if you are measuring the concentration of Cr(VI), using a blank solution that contains Cr(VI) ions is preferred.
2. Assuming the blank solution is a dilute solution containing Cr(VI) ions, it could contain a certain concentration of Cr(VI). When you measure the absorbance of this blank solution, it will account for the absorbance caused by the presence of Cr(VI) ions. This absorbance will be subtracted from the absorbance of the sample during data analysis.
3. If the concentration of Cr(VI) in the blank solution is known, its absorbance can be determined. However, if the concentration of Cr(VI) in the blank solution is not known, it may introduce some uncertainty into the calculation of the Cr(VI) concentration in the sample.
4. To minimize this uncertainty, it is recommended to determine the absorbance of a blank solution without any Cr(VI) ions (such as deionized water). This will provide a baseline absorbance value, and any absorbance measured in the blank solution with Cr(VI) can be directly attributed to the presence of Cr(VI) ions.
5. By subtracting the baseline absorbance (from deionized water) from the absorbance of the sample and the blank solution, more accurate results can be obtained for the concentration of Cr(VI) in the sample.
In summary, if the blank solution used in absorption spectroscopy contains a dilute solution with known or consistent concentrations of Cr(VI) ions, the concentration of Cr(VI) in the sample can still be accurately determined by subtracting the absorbance of the blank from the absorbance of the sample. However, using deionized water as a blank solution provides a more reliable baseline for accurately measuring the concentration of Cr(VI) in the sample.