3 Following are descriptions of four common types of mistakes that can occur whe

Question

3 Following are descriptions of four common types of mistakes that can occur when constructing a calibration curve, and incorrect calibration curves that can result. Each plot shows the data resulting from the error and the best-fit line to the erroneous data (red), and what the correct best fit line should look like (gray). Match the error to the calibration curve explain your reasoning and briefly describe how the error would impact the measurement of the molar absorptivity for the dye in question. Curve Error Description Student did not rinse the volumetric flask with deionized water in between each standard solution preparation. Student rinsed the volumetric pipette with deionized water in between each standard solution preparation, rather than conditioning it with the solution to be diluted Student created the standard solutions correctly, but associated the absorbance readings with the wrong concentrations when recording data. 4 Student made three identical dilutions of Standard 1, instead of diluting Standard 2 to obtain Standard 3, and diluting Standard 3 to obtain Standard 4. Curve A Error that lead to this curve Reasoning 1.00 0.80 0.60 0.20 0.00 Relative to the actual value, the molar absorptivity predicted by this curve will be: Concentration (10-5 molL) higher lower the same Error that lead to this curve Curve B Reasoning 0.80 0.60 0.20 0.00 Relative to the actual value, the molar absorptivity predicted by this curve will be: Concentration (10s mol/L) higher lower the same

Explanation / Answer

In the first graph the observed absorbance is higher than normal indicating the solution is more concentrated than original value. Second observating is the absorbance is nearly constant. This is because the solutions are not diluted. So this due to error D.

In the second graph there is no relationship between standard curve and actual results. This is indicating that the student didn't enter the values correctly and interchanged the values with concentration. This is due to error C.

In third graph the values are nearly same and the practical curve is slightly more than theoretical curve. This is indicating that the concentration of the solution is slightly increased in each trial. This is because the student didn't wash and rinse the volumetric flask with water. The previous higher concentrated solution was left in the container and the concentration is increased. So it is due to error A

In the last graph the values are nearly same but the practical curve is slightly less than theoretical curve. This is indicating that concentration of the solution is slightly diluted in each trial. This is because deionised water is left in volumetric flask and diluting the solution. So student didn't condition the volumetric flask with standard solution and this is error B.

Molar absorptivity is the calculated from the slope of the curve. In experiment no 1 and 3 the slope is less than the theoretical value. So Molar absorptivity will be less than original value.

For experiment 4 the slope is higher than the original value so molar absorptivity will be higher than original value.

In experiment 2 the slope is nearly same (even though the sign of slope is opposite). So we will get nearly same molar absorptivity.  

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