The concentration of manganese in steel can be determined spectrophotometrically by dissolving the steel in acid and oxidizing Mn to MnO4?. The resulting solution is purple and the absorbance at 525 nm can be monitored. A standard solution containing 0.228 mM of Mn has an absorbance of 0.343 in a 1.00 cm cell. The absorbance of an unknown solution of Mn is 0.404. What is the molar concentration of Mn in the unknown solution