Iron, Steel and Other Metals Flashcards
what is rusting?
rusting is the chemical process by which iron is oxidized to form rust
what is the chemical name for rust?
hydrated iron(III) oxide
rust word equation?
iron -> iron(III) oxide -> hydrated iron(III) oxide
rust symbol equation?
Fe(s) -> Fe2O3(s) -> Fe2O3 xH2O(s)
properties of iron?
- grey
- shiny
- malleable
properties of hydrated iron(III) oxide?
- brown
- brittle
- dull
what two substances does rust require?
- oxygen
- water
what are the two stages of rusting?
- iron is oxidized by oxygen to form iron(III) oxide - Fe has gained oxygen and it has also lost electrons to form Fe3+ ions, for both reasons it has been oxidised
- iron(III) oxide is hydrated by water - the amount of water gained by the iron(III) oxide varies a lot
what are the three methods that can prevent rusting?
- using barriers
- sacrificial protection
- galvanising
how can rusting be prevented by using barriers?
- coating the iron in paint, oil, grease or plastic prevents the iron from coming into contact with oxygen or water (this only works as long as this coating is intact - as soon as it breaks rusting happens)
- you choose the coating material depending on the use for the iron - oil or grease for moving parts (e.g. bike chains), paint or plastic for larger more stationary objects (e.g. buckets)
how can rusting be prevented using sacrificial protection?
- attach a block of a more reactive metal (e.g. magnesium) to the iron
- this works by displacing the iron from rust as soon as the rust forms
- the downside to this method is that the block of magnesium has to be replaced often
what is the word equation for the magnesium rust displacement reaction?
magnesium + iron(III) oxide -> magnesium oxide + iron
what is the symbol equation for the magnesium rust displacement reaction?
3Mg(s) + Fe2O3(s) -> 3MgO(s) + 2Fe(s)
how can rusting be prevented using galvanising?
- this method specifically involves coating the iron in zinc
- coating prevents oxygen and water from coming in contact with the iron, but even if a crack appears, zinc is more reactive than iron so acts as sacrificial protection as well
what is an alloy?
alloys are mixtures of a metal with one or more other elements, usually other metals or carbon
commonly known alloys?
- steel (elements = iron + carbon)
- brass (elements = copper + zinc)
- bronze (elements = copper + tin)
why are alloys harder than pure metals?
the different sized atoms/ions prevent the layers of metal ions sliding over each other - this means the alloy is less malleable
iron - elements, use and reason?
elements = Fe
use = making steel
reason = steel is more useful than iron
low-carbon steel - elements, use and reaction?
elements = Fe + 0.1% C
use = ships, cars, bridges etc.
reason = strong, but low-carbon so can be hammered into various shapes
high-carbon steel - elements, use and reaction?
elements = Fe + 1% C
use = tools e.g. knives, screwdrivers
reason = high-carbon so less malleable and stiffer than low-carbon steel
stainless steel - elements, use and reaction?
elements = Fe + 1% C + 10% Cr
use = cutlery, cooking utensils, kitchen sinks
reason = Cr forms oxide layer than resists corrosion, so stays shiny and clean
copper - elements, use and reaction?
elements = Cu
use = wires, cooking pans, water pipes
reason = excellent conductor of electricity, excellent conductor of heat, unreactive and malleable
aluminium - elements, use and reason?
elements = Al
use = aircraft bodies, power cables
reason = low density and high strength, low density and conducts
