Chemistry Math Question

Question

A steel railroad bridge uses a zinc sacrificial anode to limit the extent of oxidation of the steel. If a 8 kg anode is completely ozidized to Zn²⁺ over the course of 17.2 years, compute the average current flowing through the anode.

Answer 1

Hi. I answered this when originally posted, but will add this using a conversion of 17.2 years instead of 19.2 years and 8 kg of Zn instead of 9.4 kg

How many moles of Zn are there?

8 kg x 1000 g/kg x 1 mol/65 g = 123 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 123 moles = 246 moles electrons in 17.2 years.

The question asks for the average CURRENT. Current is usually expressed in amperes (amps) and 1 amp is equivalent to 1 coulomb (C)/second. 1 amp = 1C/sec.

Also, 96500 C = 1 mole of electrons.

246 mol e- x 96500 C/mol e = 25,476,000 C. This is for 17.2 years. We now convert this to current (amps)

25,476,000 C/17.2 x 1 yr/365 days x 1 day/24 hrs x 1 hr/3600 sec = 0.04697 C/sec = 0.05 amps = 50 mA