A team of students used the Ocean Optics spectrometers to collect absorbance wit
ID: 1070250 • Letter: A
Question
A team of students used the Ocean Optics spectrometers to collect absorbance with three different wavelengths and then plotted these sets of absorbance against concentration.
A) Which line is MOST LINEAR? Briefly explain how you determined that?
B) Using the equation of the line you feel is most linear, calculate the concentration of the unknown? (ignore the pencil marks)
C) On the graph above, CIRCLE the lowest absorbance limit for a Beer's Law plot ?? (NOTE: readings less than this absorbance have large errors in estimating concentrations)
0.900 0.800 0.700 0.600 0.500 0.400 0.300 0.200 0.100 0.000 0.000 0.020 calibration curve of Nickel (ll) complex y 5.1025x +0.012 0.98772 y 3.2075x 0.011 R2 0.94995 y 2.2625x 0.026 R2 0.96782 495 nm 722 nm 658 nm 0.040 0.060 0.080 0.100 0.120 0,140 0.160 0.180 Concentration (M)Explanation / Answer
A) If R-squared = 1, then all the points lie on that line. When R-squared is close to 1, we assume that the behaviour of the y-values is, at least in part, determined by the x-values. Error is 0 when R-squared = 1. As, R2 = 0.98772 is closest to 1 out of all three values, therefore, line at 495 nm is the most linear one.
B) y=5.1025x +0.012. is the equation therefore we should consider for the further calculations.
0.500 = 5.102x +0.012
0.488 = 5.102x
x = 0.09564 M
C) The linear relationship between concentration and absorbance is both simple and straightforward. If the concentration of the solution is halved so is the absorbance. This relationship is a linear for the most part. However, under certain circumstances the Beer Lambert relationship breaks down and gives a non-linear relationship. Beer law and Lambert law is capable of describing absorption behavior of solutions containing relatively low amounts of solutes dissolved in it (<10mM). Absorbance below 0.01 therefore, will give faulty readings.
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