Question

Final Concentration (ppm)	absorbance (a.u.)
0.022	0.922
0.016	0.858
0.013	0.589
0.009	0.403
0.005	0.174

I cannot figure out the first question, y=?

Based on the data above and using linear regression, determine the relationship between absorbance (y) and concentration (x).

y = _______ x

What is the concentration of a solution with an absorbance of 0.71 a.u.?

Answer: 0.0156 ppm

Answer 1

Note that absorbance and concentration are directly related by the Beer's law equation given as follows:

Where

A = absorbance

c = concentration

l = path length

Hence, plotting absorbance, A in y axis and concentration in x axis, we should get a straight line with slope .

Hence, for the given data, we will get the following linear fit plot:

Now, from the graph, the linear fit equation is

Where y is the absorbance and x is the concentration in ppm.

Hence, your answer to the first part of the question is

.

Now, for a solution with absorbance 0.71, we can calculate the concentration by putting y = 0.71 in the above equation

Hence, the concentration of the unknown solution is 0.0156 ppm.