A 25.00 mL of a sample containing both Fe3+ and Cu2+ required 16.06 mL of 0.05083M EDTA to completely titrate both cations. A 50.00 mL sample of the unknown was treated with NH4F to protect the Fe3+. The Cu2+ was then reduced and masked with thiourea. Addition of 25.00 mL of the 0.05083 mL EDTA liberated the Fe3+, forming a complex. The excess EDTA from this reaction required 19.77 mL of 0.01883 M Pb2+ standard solution to reach an end point. Calculate [Cu2+] in the unknown