Question

The concentration of Cu2+ in seawater is determined by anodic stripping voltammetry at a hanging mercury drop electrode after first releasing any copper bound to organic matter. To a 25.00-mL sample of seawater 1 mL of 0.5 M HNO3 and 1 mL of 0.1% H2O2 are added. The sample is irradiated with UV light for 6 hr and then diluted to volume in a 50-mL volumetric flask. Deposition of Cu2+ takes place at –0.45 V versus an SCE for 10 min, producing a peak current of 22.5 (arbitrary units). A second 25.00-mL sample of the seawater is treated identically, except that 0.5 mL of a 10.00 μM solution of Cu2+ is added, producing a peak current of 32.1 (arbitrary units). What is the concentration of Cu2+ in seawater?

0.468 µM

0.365 µM

1.652 µM

1.352 µM