Redox, rusting and iron Flashcards
What is a Redox reaction?
One which oxidation and reduction occur at the same time
What is oxidation?
Gain of oxygen, loss of hydrogen and loss of electrons
What is reduction?
Loss of oxygen, gain of hydrogen and gain of electrons
What redox reaction occurs during the extraction of iron in a blast furnace?
Iron oxide + carbon monoxide - iron + carbon dioxide
Fe2O3 + 3CO - 2Fe + 3CO2
Iron loses oxygen and gains three electrons.
Carbon monoxide gains oxygen.
What is the oxidation reaction in the rusting of iron?
Iron + oxygen + water - hydrated iron(lll) oxide
Iron loses three electrons and gains oxygen.
What is the redox reaction during the extraction of aluminium by electrolysis?
Aluminium oxide (bauxite) - aluminium + oxygen
2Al2O3 - 4Al + 3O2
Aluminium loses oxygen and has gained three electrons.
Oxide ions lose two electrons.
What is the reduction reaction during the production of ammonia in the Haber process?
Nitrogen + hydrogen - ammonia
N2 + 3H2 - 2NH3
Gain of hydrogen
How can rust be prevented?
Barriers method - creates a physical layer that separates iron from O2 and H2O e.g. plastic coating fridges.
Oil - generates a protective layer on the metal e.g. bike chain.
Sacrificial protection - more reactive metal oxidises more readily than iron e.g. magnesium on boats.
Alloying - chromium reacts with oxygen to form a protective oxide layer.
Rust is speeded up by salt.
What does a deliquescent metal do?
Absorbs moisture from the air and dissolves in the absorbed water, forming a solution e.g. sodium hydroxide
Step 1 of iron extraction in a blast furnace (Formation of Reducing Agent)
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. This is oxidation.
Carbon (coke) + oxygen (hot air) - carbon dioxide
Step 2 of extraction iron in a blast furnace (Forming the Reducing Agent)
The carbon dioxide reacts with more coke to carbon monoxide. This is redox reaction.
Carbon dioxide + Carbon (coke) - Carbon monoxide
Step 3 of extraction iron in a blast furnace (Reduction of Iron Oxide to Iron)
The carbon monoxide reduces the iron oxide (haematite) to iron. Carbon monoxide is the reducing agent. This is a redox reaction.
Iron(lll) oxide + carbon monoxide - Iron + Carbon dioxide.
Fe2O3 + 2CO - 2Fe + 3CO2
Step 4 of extraction iron in a blast furnace (Removal of the impurity)
The main impurity is in iron ore is sand. The limestone added thermally decomposes to calcium oxide.
Calcium carbonate (limestone) - Carbon dioxide + Calcium Oxide.
Step 5 of extracting iron in a blast furnace (Removal of the impurity)
Calcium oxide combines with sandy impurities (silicon dioxide), in the iron ore to from slag (calcium silicate).
Calcium oxide (base) + Silicone dioxide (acidic) - Calcium silicate (salt)
What is calcium silicate?
Known as slag. It is less dense than iron. Slag floats on top of iron. Slag is used to make roads, landfill and foundations for buildings.
The hot want 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.
Uses of iron
It is a cheap metal because the ore is in large quantities. It is used in many structures and bridges due to its strength.
What is the main impurity of crude iron?
Carbon and the crude iron is turned into steel by lowering its carbon content (too much carbon makes iron brittle) and adding other metals (alloy formation)
