Calculate the Concentration of Unknown Solution from Standard Curve?

i) First take different volume of standard solution (say 0.2, 0.4, 0.6, 0.8, 1.0 ml) and then calculate the concentration of the standard solution added in each tube.

ii) Measure the optical density for each concentration in a spectrophotometer or colorimeter.

iii) Next, plot the concentration of the standards solution (taken on the x axis) and the corresponding OD (taken on the y axis) and the graph is prepared to give a standard curve which is a straight line (since it obeys Beer's law).

iv) Now take the unknown solution (say 1ml) and measure its OD reading. Suppose the value obtained is 0.40. Plot it on the y-axis of the standard curve (already prepared for the standard solution)

The concentration obtained is 275. This is the concentration of our unknown solution for the volume that we took (say1 ml).