A standard curve was produced using absorbance values of prepared standards obtained by UV spectrophotometry. The standards were made using concentrated hydrochloric acid as opposed to the 1N HCl that the lab manual says should be used. Because of this my absorbance values are all over the place decreasing when they should be increasing. I thought the effect of the concentrated acid would cancel as I used the concentrated acid as the reference but it appears that was not the case. Does the high concentration of the HCl effect the beers law relationship? I'm trying to research but not coming up with anything. I'm trying to explain in my discussion how the error affected my results. Any help is greatly appreciated.

Question

A standard curve was produced using absorbance values of prepared standards obtained by UV spectrophotometry. The standards were made using concentrated hydrochloric acid as opposed to the 1N HCl that the lab manual says should be used. Because of this my absorbance values are all over the place decreasing when they should be increasing. I thought the effect of the concentrated acid would cancel as I used the concentrated acid as the reference but it appears that was not the case. Does the high concentration of the HCl effect the beers law relationship? I'm trying to research but not coming up with anything. I'm trying to explain in my discussion how the error affected my results. Any help is greatly appreciated.

Answer 1

The concentration of the hydrochloric acid (HCl) can indeed affect the Beer's law relationship in UV spectrophotometry.

Beer's law states that there is a linear relationship between the concentration of a solute and the absorbance of light passed through it. However, this relationship holds true only when certain conditions are met, including that the solution is within the linear range of the instrument and that there are no interfering substances present.

In your case, by using concentrated hydrochloric acid instead of the specified 1N HCl, you likely introduced an interference or altered the linear range of the instrument. Concentrated hydrochloric acid has a much higher concentration than 1N HCl, which means it has a significantly different composition. This difference in composition may alter the wavelength at which the acid absorbs light, leading to incorrect or inconsistent absorbance readings.

To explain the error in your discussion, you can outline how the non-standard HCl concentration affected your results. Mention that concentrated HCl may have different absorption properties at the wavelength of interest, leading to deviations from Beer's law. Additionally, discuss how the high concentration of HCl might have caused the instrument to reach its upper limit of linearity, resulting in inconsistent absorbance values.

To mitigate the error, it is crucial to use the specified 1N HCl as stated in the lab manual. By using the correct reagent, you should achieve more accurate and reliable results that uphold the assumptions of Beer's law.