PPT Slide

Applying the Relationship Among Current, Time, and Amount of Substance

Problem: A technician needs to plate a bathroom fixture with 0.86 g of

chromium from an electrolytic bath containing aqueous Cr2(SO4)3. If

12.5 min is allowed for the plating, what current is needed?

Plan: We write the half-reaction for Cr3+ reduction. We then know the

number of moles of electrons per mole of Cr, and can calculate the

current needed to do the electroplating.

Solution: Writing the balanced half-reaction:

Cr3+(aq) + 3 e- Cr(s)

e- transferred: 0.86 g Cr x x = 0.050 mol e-

1 mol Cr

52.00 g Cr

3 mol e-

1 mol Cr

Calculating charge transfer:

Charge (C) = 0.050 mol e- x = 4.8 x 103 C

9.65 x 104 C

1 mol e-

Calculating the current:

Current (A) = = x = 6.4 C/s = 6.4 A

charge (C)

time (s)

4.8 x 103 C

12.5 min

1 min

60 s