Answer Happy

5 Points. Why must you use a solution that is 0.5 M HNO3 and 0.5 g/L sulfamic acid as your blank as opposed to distilled water? The blank must always have the same chemical composition as the solvent of the solutions you are using. A This ensures any incidental light absorbed by the solvent can be subtracted out during measuring to give a more accurate absorbance (and thus concentration) of a mixture. It doesn't matter what you use for a blank as long as you calibrate the Spec-20 with that blank before using it. Without using a blank, the measured absorbances will be lower than expected, leading to unreliable results. Nitric acid and sulfamic acid, when dissolved in water, cause the initial solutions to becomcolored. As a result, the absorbance of a solution containing only those chemicals must be measured as a blank so it can be subtracted out from each mixture, giving more accurate absorbance measurements for each equilibrium mixture.