Unit 6 - Metals And The Reactivity Series
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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
What happens at the anode and cathode (aluminium extraction)
Cathode : reduction Al+++ (ions) + 3e- –> Al (atoms) Anode : oxidation 2O– (ion) - 4e- –> O2 (molecules)
Test for cation Cu++
Add to sodium hydroxide If test is positive as blue precipitate is formed
Describe the laboratory preparation of carbon dioxide
Use the thermal decomposition of metal carbonates Metal carbonate -heat-> metal + carbon dioxide
How was the reactivity series made
It’s based on the reactions of the metals and their compounds
What is the aluminium ore used (before purified aluminium oxide is used)
Bauxite
What is meant by endothermic
Takes in heat, absorbs heat
What makes a reaction endothermic
Strong forces/bonds between within the compounds need to be broken
Equation for cryolite (solvent for aluminium)
Na3AlF6
Why are the electrodes (electrolysis) made of carbon
• graphite conducts electricity - high melting point