General Chemistry Electrochemistry Math Question 5

Question

A steel railroad bridge uses a zinc sacrificial anode to limit the extent of oxidation of the steel. If a 9.4 kg anode is completely ozidized to Zn²⁺ over the course of 19.2 years, compute the average current flowing through the anode.

Answer 1

How many moles of Zn are there?

9.4 kg x 1000 g/kg x 1 mol/65 g = 145 moles Zn

Zn ==> Zn²⁺ +2e- half reaction for Zn acting as an anode and being oxidized

Each mole of Zn oxidized liberates 2 moles of electrons

Moles of electrons generated = 2 electrons/mole x 145 moles = 290 moles electrons

Current = amps = coulombs/sec

290 mol electrons/19.2 yrs x 1yr/12mo x 1 mo/30 day x 1 day/24 hr x 1 hr/3600 sec = 4.9x10^-7 mol e-/sec

4.9x10^-7 mol e-/sec x 1 F/mol e- x 96450 coulombs/F = 0.05 coulombs/sec = 0.05 amps = average current