Unit 6 - Metals And The Reactivity Series Flashcards
The reactivity series
Potassium, sodium, lithium, calcium, magnesium, aluminium, (carbon), zinc, iron, tin, lead, (hydrogen), copper, silver, gold, platinum
How are the methods of extraction related to the reactivity of a metal
A metal can only be extracted in a blast furnace if the metal is less reactive than carbon. Otherwise, electrolysis is used
Main reactions involved in the extraction of iron (blast furnace)
Coke is reacted with oxygen to form CO2
C (Coke)+ O2 –> CO2
This Produces heat to decompose the limestone
CaCO3(limestone) –> CaO + CO2
Carbon dioxide is reduced to carbon monoxide by more Coke
CO2 + C –> 2CO
Carbon monoxide is the main reducing agent
3CO + Fe2O3 (haematite) –> 2Fe + 2CO2
Limestone removes impurities such as silica which would make the iron hard and brittle
CaO + SiO2 (silica) –> CaSiO3 (slag)
Molten slag sits on top of the molten iron to stop re-oxidisation. Slag is later used for breeze blocks and motorways. Hot gases emerging from top of blast furnace are mainly nitrogen from the air (with some CO and CO2)
Conditions under which iron rusts
Iron will react with damp air to form hydrated iron oxide. Water and oxygen are needed
How can rusting be prevented
Using oil, grease, paint, plastic, or galvanising to stop air and water reaching the surface
What is galvanising
Dipping the iron into molten zinc so that the iron is completely coated
What is sacrificial protection
A way of stopping rusting.
By attaching a block of metal more reactive than iron, it will corrode before the iron does. Zinc is often used
What are iron alloys known as
Steels
What is mild steel used for and why
Motor car bodies
Malleable
What is hard steel used for and why
Tools such as chisels, files, and saws
It is hard and strong
What is stainless steel used for and why
Cutlery, sinks, sculptures
Does not rust
Why is titanium steel used for and why
Edges of high speed cutting tools, armour plating
Low density, high strength, doesn’t rust
Test for Fe++ compounds
Dissolve in distilled water
Add sodium hydroxide solution
Fe++ compounds form a moss green gelatinous precipitate : Fe(OH)2
Test for Fe +++ compounds
Dissolve in distilled water
Add sodium hydroxide solution
Fe+++ compounds form a foxy brown gelatinous precipitate : Fe(OH)3
Extraction of aluminium from purified aluminium oxide
Aluminium is extracted by electrolysis
First, the aluminium oxide is dissolved in molten cryolite (Na3AlF6) which acts as a solvent as well as reducing the melting point from 2050 degrees to ~950. This reduces the energy needed (cheaper) and increases the conductivity of the Al2O3
Both the electrodes are made of graphite (C) as it conducts electricity and is cheap
The aluminium metal then forms at the cathode
Al+++ add 3e- –> Al (reduction)
The oxygen atoms are then formed at the anode
2O– minus 4e- –> O2 (oxidation)
The positive electrodes have to be replaced often as the oxygen reacts with the carbon to form CO2
