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A brief summary of the topic on Metals
Properties of Metals
Metals have very high densities - A large number of metal atoms are closely packed in the giant metallic lattice |
Metals are good conductors of heat and electricity - presence of sea of delocalised electrons(help to conduct heat and electricity) |
Metals are soft - When a force is applied, layer of metal atoms will slide over one another |
Metals are malleable and ductile - When a force is applied, layer of metals slides over one another without disrupting metallic bonds |
Metals have a high melting point - Large amount of energy is required to overcome the strong metallic bonds between lattice of positive cations and sea of delocalised electrons |
Remember: Metallic bonding in metals
Alloys
What is an alloy - mixture of a metal with one or more other elements |
Effect of alloying - makes the original metal stronger, harder and more resistive to corrosion |
How does alloying strengthen metals - Neat, regular rows of metal atoms are disrupted by the presence of a new atom of a different size. Layers of metal atoms can no longer slide over one another when a force is applied. Hence the metal is stronger and harder |
Common alloys - Steel/ Brass |
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Reactivity Series
K |
Na |
Ca |
Mg |
Al |
C |
Zn |
Fe |
Sn |
Pb |
H |
Cu |
Ag |
Au |
Trend of reactivity series: Reactivity decreases down the series
Reactions that establish the reactivity series
Metal + Water = Metal hydroxide + Hydrogen |
Metal + Steam = Metal oxide +Hydrogen |
Metal + HCL = Metal Chloride + Hydrogen gas |
Metals that react with cold water - Potassium to Magnesium (decreasing vigour) |
Metals that react with steam: Potassium to Iron |
Metals that react with hydrochloric acid: Potassium to Iron |
Why does lead not react with water/steam/HCl = Formation of lead hydroxide, lead oxide, lead chloride which are all insoluble (form layer) |
Reactions based on reactivity series
Displacement - A more reactive metal displaces a less reactive metal from its salt solution/ oxide (more reactive metal in solid state/less reactive metal in ion state) |
Thermal Stability of carbonates - Thermal stability of carbonates decreases down the reactivity series |
Most thermally stable carbonates - Group 1 carbonates |
Thermal decomposition of carbonates= metal oxide + carbon dioxide |
Thermal decomposition of silver carbonate= silver + carbon dioxide + oxygen |
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Extraction of metals
Electrolysis of molten ore - Potassium to Aluminium |
Reduction of carbon : Below Carbon in reactivity series |
Reduction of hydrogen : Iron - Copper |
Found chemically uncombined: Silver and Gold |
Extraction of iron - Use carbon to reduce haematite to form molten iron ( blast furnace) |
Rusting
Rusting - oxidation of iron to form hydrated iron(III) oxide |
Conditions for rusting - Both oxygen and water |
Prevention of rusting: Protective layer(oil/paint), Sacrificial Metals, Use of alloys |
Protective layer (must cover entire surface): prevents iron from coming in contact with oxygen and water—prevents rusting |
Sacrificial Protection(no need to cover entire surface): Metal A is more reactive than Metal B. Metal A acts as a sacrificial metal and corrodes in the place of iron |
Example of sacrificial protection- Galvanising(Zinc) |
Use of alloys - alloys are more resistive to corrosion |
Do not use sodium and potassium as sacrificial metals (too reactive)
Use zinc/magnesium
Recycling of metals
Why must we recycle metals - Metals are finite resources. It is our responsibility to conserve metals for future purposes |
Problems with mining: contribute to environmental pollution, burning of fossil fuel, contributes to unnecessary waste(take up landfill space) |
Cons of recycling: Expensive process |
Why is aluminium unreactive?
Reacts with oxygen in surrounding air to form aluminium oxide. Aluminium oxide forms an impervious layer on the surface of the metal |
Prevents metal form coming into contact with the other reactant |
Prevents metal form coming into contact with the other reactant |
Hence aluminium is unreactive |
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