Importance of calibration curve?

Question

recently,I did a experiment to determine the unknown concentration of a solution by using spectrophotometer,then we plot a graph of absorbance vs concentration.At the last part,we are ask the importance of calibration graph,in fact,I don't really know its importance.

Answer 1

You can use it to determine the concentration of an unknown just by measuring the absorbance.  

Suppose on your curve you have absorbance from 0.18 to 0.35 from concentrations of 0.5 to 5 mM which you made from measuring the absorbance for several solutions of known concentration.  Then you have a sample fo the same solution but you don't know the concentration.  You can use the curve (for example, its equation if it is a straight line) to determine the unknown concentration if you determine its absorbance.