Chemistry · Chapter 17

Plate Metal, Stop Rust

Up top, pay electricity to force a reaction uphill and let Faraday's law tell you exactly how many grams land on the cathode. Down below, bolt a second metal onto iron and find out which one the weather eats.

Electrolysis the deposit grows with charge

An electrolytic cell plating metal onto the cathode Current and time turned into grams, one step at a time

Corrosion the lower metal loses

Iron bolted to a second metal, with the anode wasting away

What are you plating?

2.00 A
30 min

How much metal

4.02grams n = 1
Charge passed: 3600 C
Moles of electrons: 0.03731 mol
Moles of metal: 0.03731 mol
Coat on a 100 cm² plate: 3.8 µm thick

Bolt something onto the iron

10.0 µA/cm²
5.0 years

Which one is eaten

Feis the anode iron rusts
Corrosion cell potential: 0.84 V
Metal lost each year: 9.1 g
Metal lost in that time: 45 g
No protection
Iron is on its own
Air and water set up a cell on the surface. The iron is the anode, so the iron dissolves.

The voltage tells you which metal goes first, not how fast. Speed depends on the current, which is why the current is a control of its own here.