6 Cupper Cu was determined in an alloy sample by UVvisible s

6. Cupper (Cu) was determined in an alloy sample by UV-visible spectrophotometry. The standard addition method was used. When exactly 5.0 mL of 1.00 g/L Cu standard solution was added to 100.0 mL of the sample solution, the blank-corrected absorption changed from 0.26 to 0.60. Calculate the concentration of Cu in the sample solution assuming the absorbance was directly proportional to the analyte concentration. (15 pts)

Solution

concentration of standard in the sample = 1 g/L x 0.02 ml/100 ml = 2 x 10^-4 g/L

let Cx be concentration of unknown in solution

Cx/(Cx + 2 x 10^-4) = 0.26/0.6

0.6Cx = 0.26Cx + 5.2 x 10^-5

Cx = 1.53 x 10^-4 g/L is concentration of analyte