Year 12s: what will be the first way you research your future options? >>

Chemistry(METALS)

abdullahAK

Question's pic in the following post.

Reply 1

abdullahAK

Can anyone answer the question below and explain as well.
Help will be appreciated.

oo.PNG22.7KB

Reply 2

Nour M.

I'm here to the rescue :biggrin:

Now, what you've got here is known as galvanisation (coating steel/iron with zinc). Iron has this annoying tendency of oxidising into iron oxide (rust), which is much weaker and more brittle, when exposed to water and oxygen (found in the air). So in order to stop this, we need some sort of mechanism to stop iron from rusting and so galvanisation is used. Zinc can prevent rusting by forming a physical barrier between iron and water/air. However, zinc can chip away so what happens if the iron becomes exposed?!?!?! We need to refer to the metal reactivity series:

Potassium
Sodium
Lithium
Calcium
Magnesium ↑
Aluminium ↑ Increasing reactivity
Zinc ↑
Iron
Copper
Silver
Gold

It's clear that Zinc is more reactive than Iron as it's higher in the reactivity series. This means that if zinc and iron were placed together, the zinc will be more likely to oxidise as it's more willing to lose electrons than iron. Galvanisation is based on this principle. We use zinc as a 'sacrificial' coating in order to protect the iron. Now what is the reason preventing the galvanised iron from oxidising even though it's clearly exposed to the atmosphere? In order to answer this, we need to understand what is going on beneath the surface. Zinc is still being oxidised right? Now what do metals form when they oxidise? ELECTRONS! So zinc loses electrons when it's oxidised. These electrons are then transferred to any iron ions which may have formed as a result of oxidation (rusting). The iron ions gain these electrons and are reduced back to iron, reversing the effects of rusting. This means that overall the iron won't be losing electrons as it's constantly supplied with some due to the oxidising zinc aka no rust. So even if there is a break in the zinc coating, exposed iron won't rust as long there's still some zinc left to oxidise.