Hi.
We performed an experiment on UV-Vis Spectrometry, by testing the absorbance of KMnO4 and KCr2O7 solutions at different concentrations. We prepared the dichromate solutions with dilute sulfuric acid. Why didn't we use water, what is the purpose of sulfuric acid?
Hi! In UV-Vis Spectrometry, the purpose of using dilute sulfuric acid instead of water is to create an acidic environment for the reaction between the potassium dichromate (KCr2O7) and the sulfuric acid (H2SO4). This reaction transforms the dichromate ion (Cr2O7^2-) into a chromate ion (CrO4^2-) in the solution. The presence of the chromate ion allows for sufficient absorption of ultraviolet and visible light, which is necessary for the UV-Vis analysis.
Using water alone would not provide the required acidic conditions for this reaction to occur. The acid helps maintain a stable environment that is necessary for accurate and reproducible UV-Vis measurements. Additionally, the acid can also contribute to stabilizing the potassium dichromate solution and preventing any unwanted chemical reactions that might occur with other species present in the water or the sample itself.
By using dilute sulfuric acid as a solvent, you ensure the optimal conditions for the formation of chromate ions and accurate UV-Vis analysis.