Question

During a spectrophotometric analysis of an unknown, you measure your solution's absorbance, and the value is higher than the highest standard you used to make your standard curve. What should you do to make sure you can use your standard curve to determine the unknown's concertration?

A) Dilute the unknown so that it will have an absorbance within the standard curve. Once the diluted unknown concentration is determined, the full strength concentration can be calculated if the dilution process is recorded. Beer's law only applies to dilute solutions, so diluting the unknown is better than making new standards.B) A new set of standard solutions should be made to accommodate the unknown solution concentration. Beer's law is linear even at high concentrations, but a new concentration curve should be made to illustrate this point. Even though it is more work, making new standard solutions is a better method of obtaining correct results.C) There is no need to do anything to the unknown solution. Beer's law describes the relationship between absorbance and concentration. This relationship is linear even at high concentrations, so the standard curve equation will apply for any concentration of that specific solution.D) Pour a specified amount of the unknown solution into each of the standard curve solutions. This process will increase the absorbance of the solutions, to the point that the unknown solution's absorbance will fit within the standard curve appropriately.

Answer 1

A) Dilute the unknown so that it will have an absorbance within the standard curve. Once the diluted unknown concentration is determined, the full strength concentration can be calculated if the dilution process is recorded. Beer's law only applies to dilute solutions, so diluting the unknown is better than making new standards.

Step-by-step explanation:

Beer's law states that absorbance is proportional to the concentrations of the absorbing species. This is verified in the case of diluted solutions (0≤0.01 M) of most substances. As a solution gets more concentrated, solute molecules interact between themselves because of their proximity. When a molecule interacts with another, the change in their electric properties (including absorbance) is probable. That's why the plot of absorbance versus concentration stops being a straight line, and Beer's law is no longer valid.

Therefore, if the absorbance value is higher than the highest standard, dilutions should be made. Once this concentration is determined, the full strength concentration can be calculated with the inverse of the dilution.