Redox, Rusting And Iron Flashcards
Oxidation definition
Gained of oxygen, loss of hydrogen or loss of electrons
OIL
Reduction definition
Reduction is loss of oxygen, gain of hydrogen or gain of electrons
RIG (Reduction is gain)
Sulfur + Oxygen —> Sulfur dioxide
Sulfur is oxidised because it has gained oxygen
2Hl —> H2 + I2
Oxidised because it lost hydrogen
2Br- —> Br2 + 2e-
Oxidised because it has lost electrons
N2 + 3H2 —> 2NH3
Reduced because it has gained hydrogen
Rust is…
Hydrate iron(iii) oxide Fe2O3.xH2O
What does the deliquescent chemical calcium chloride do?
It removes any moisture / water
Name two other deliquescent materials
Calcium oxide and sodium hydroxide (solid)
Give 5 methods used to prevent rusting and give examples of each
- Barrier methods e.g painting gates chrome plating taps
- Oil e.g bicycle chain
- Sacrificial Protection e.g magnesium is bolted to the bottom of boats
- Alloying e.g stainless steel which is a mixture of iron and chromium
- Galvanising - layer of zinc
Galvanising definition
Galvanising is a process that bonds a layer of zinc metal onto the surface of steel. The zinc soon reacts with the air to form zinc oxide which gives a protective layer
Advantage of galvanising
Even if the zinc coating gets scratched or damaged the exposed steel will still not rust. The zinc will react instead of the iron
Sacrificial Protection definition
A more reactive metal in good contact with a less reactive metal will always react first, thereby protecting the less reactive metal from corrosion
Describe stage 1; Formation of reducing agent in the blast furnace
Hot air (oxygen) is blown in at the base of the furnace and coke burns to heat the furnace to 1500 degrees, forming carbon dioxide
C (s) + O2 (g) —> CO2 (g)
The carbon dioxide reacts with more coke to form carbon monoxide
CO2 (g) + C(s) —> 2CO (g)
Describe stage 2; reduction of iron oxide to iron
The carbon monoxide reduces iron oxide to molten iron. Carbon monoxide is the reducing agent
3CO(g) + Fe2O3 (s) —> 3CO2 + 2Fe (l)
Describe stage 3; removal of the impurity
The main impurity in iron ore is sand. The limestone added thermally decomposes to form calcium oxide
CaCO3 (s) —> CaO (s) + CO2 (g)
Calcium oxide combines with the sandy impurities (silicon dioxide) in the iron ore to form molten slag (calcium silicate)
CaO (s) + SiO2 (s) —> CaSiO3 (l)
What is calcium silicate (slag)?
Slag floats on top of iron as it is less dense than iron. It is used to make roads, landfill and foundations for buildings
How are the hot waste gases used in the blasting furnace ?
The gases, mainly nitrogen, carbon monoxide and carbon dioxide are used to heat up the air pumped into the bottom of the furnace, hence reducing energy costs
What is the main impurity in crude iron?
Carbon (pig iron)
How is the crude iron turned into steel ?
By lowering its carbon content (carbon makes iron too brittle) and adding other metals (alloy formation)
Redox reaction
A redox reaction is one in which oxidation and reduction occur at the same time
Displacement reaction definition
A displacement reaction is one in which a more reactive metal takes the place of a less reactive metal in a compound
Why is rust dangerous in construction ? (2)
- Rust weakens the metal. Iron and steel are used extensively in construction
- so rusting is a major problem due to the cost of replacing the structures
