A 25. 00 mL sample of unknown Fe³⁺ and Cu²⁺ required 16. 06 mL of 0. 050 8

A 25. 00 mL sample of unknown Fe³⁺and Cu²⁺required 16. 06 mL of 0. 050 83 mol·L^-1EDTA for complete titrated. A 50. 00 mL sample of unknown was treated with NH₄F to protect the Fe³⁺. Then the Cu²⁺was reduced and masked by addition of thiourea. Upon addition of 25. 00 mL of 0.050 83 mol·L^-1EDTA, the Fe³⁺was liberated from its fluoride complex and formed an EDTA complex The excess EDTA required 19.77 ml of 0. 01883

mol·L^-1Pb²⁺to reach an endpoint using xylenol orange. Find the concentration of Cu²⁺in the unknown.