The concentration of iron(III) can be determined by adding excess thiocyanate (SCN-) to an aqueous solution. This results in the formation of the highly colored FeSCN2+ complex ion. To do this analysis, a standard solution containing 5.00x10^-5 M Fe3+ was prepared. After addition of excess SCN-, the absorption of the standard solution =0.363 at 580 nm.

To determine [Fe3+] in an unknown solution, 1.00 mL of the solution was diluted to 50.0 mL. After addition of excess SCN-, the absorption of the standard solution =0.193 at 580 nm. What is the [Fe3+] in the ORIGINAL (UNDILUTED) solution?