Question

My question is, how do I solve this question. I don't just want the answer, I want to know step by step how to do it. A 2.5 mg/ml stock solution was diluted as described in the table below and then the absorbance of each dilution was determined and presented in the table below. Using this information, what is the concentration in mg/ml (to two decimal places) of an unknown sample with an absorbance of 0.16? (Hint: You will have to calculate the concentration in each diluted tube) Volume of 2.5 mg/ml stock Volume of buffer Abs 5 ml 0 ml 1.0 4 ml 1 ml 0.8 3 ml 2 ml 0.6 2 ml 3 ml 0.4 1 ml 4 ml 0.2 0 ml 5 ml 0.0

Answer 1

Given, the stock solution concentration (conc.) = 2.5 mg/ml. The dilutions are given, and absorbance is give.

So, in order to find out the concentartion of an unknown solution whose absorbance is 0.16, a standard graph has to be plptted taking the concentration of knowns solutions on X-axis and absorbance on Y-axis.

Given 1 ml contains 2.5 mg, therfore,

dilution	Conc. (mg/ml)	Absorbance
5	12.5	1
4	10	0.8
3	7.5	0.6
2	5	0.4
1	2.5	0.2
0	0	0

So, for an unkown whose absorbance is 0.16, the conc. can be calculated by extrapolating the unknown value on the standard graph. The conc. is 2 mg/ml.